Prepregnancy counselling, prenatal diagnosis and antenatal care

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11 Prepregnancy counselling, prenatal diagnosis and antenatal care

Chapter Contents

Prepregnancy counselling

History
General advice
Rubella
Fetal abnormality and genetic disorders
Specific medical conditions

Prenatal diagnosis

Screening tests
Structural abnormalities
Diagnostic tests
Ultrasound in pregnancy
Other ultrasound screening tests
Cervical length

Antenatal care

Booking (6–12 weeks)
16 weeks
25 weeks
28 weeks
31 weeks
34 weeks
36 weeks
38 weeks
40 weeks
41 weeks
Obstetric-led care
Rhesus disease and other red-cell alloimmune antibodies
Antenatal education
Seat belts in pregnancy
Flying in pregnancy

Summary

Prepregnancy counselling

Many pregnancies are unplanned but some women will request prepregnancy advice from their general practitioner (GP). At other times the discussion may take place opportunistically, for example during a routine gynaecology appointment or in counselling after a miscarriage. It is very important that women with specific medical problems such as diabetes, epilepsy and heart or renal disease are referred for prepregnancy assessment and management by a specialist obstetrician or physician. The aim of prepregnancy counselling is to optimize the outcome of the pregnancy for the fetus and to minimize the effect of pregnancy on any medical problems in the mother.

History

A detailed gynaecological, obstetric and medical history should be taken. Previous pelvic pathology or infection may affect the likelihood of conception and risk of ectopic pregnancy. Previous miscarriages may suggest investigations for recurrent miscarriage are indicated. In the obstetric history women should be questioned about previous fetal abnormalities (e.g. neural tube defects) or medical problems (e.g. deep-vein thrombosis), which may need to be addressed prior to a new pregnancy. A family history will also highlight any increased risk of inherited fetal abnormalities or gene disorders (such as haemoglobinopathies, muscular dystrophy or cystic fibrosis), which indicate referral for genetic counselling.

Women should be asked about any medications, whether prescribed or over-the-counter, as these may have an effect on either fertility or the development of the fetus. A social history should include smoking, alcohol and recreational drug use.

General advice

Timing of intercourse

Women are most likely to become pregnant by having intercourse two to three times per week. The most likely conception is by intercourse during the 6 days prior to ovulation (days 8–14 in a regular 28-day cycle).

Smoking

Smoking is associated with intrauterine growth restriction, prematurity, respiratory disease in infants and cot death. Women should stop smoking and be offered counselling support if necessary. Partners should also stop because of the risks of passive smoking. As smoking in men reduces sperm count this should also encourage cessation if there is a history of fertility problems.

Alcohol

Excessive alcohol in pregnancy causes fetal alcohol syndrome (fetal growth restriction, neurological impairment and facial deformities). Moderate alcohol intake causes an increased spontaneous miscarriage rate and lower birth weight and is associated with abruption and preterm labour. No adverse effects are known to occur with intake less than 15 units per week but, in practice, many women choose to avoid alcohol completely in pregnancy.

Recreational drugs

Marijuana itself does not affect pregnancy outcome, though it is often associated with tobacco smoking or the use of other harmful drugs. Ecstasy may be associated with heart and limb defects in the fetus. Both cocaine and crack cocaine lead to prematurity, stillbirth, abruption and growth restriction. Opiates (including methadone) cause growth restriction, premature delivery and stillbirth as well as neonatal addiction. Women using these drugs should be carefully managed with the local drug addiction team, to limit drug use prior to and during pregnancy. They should consider preconceptual human immunodeficiency virus (HIV), hepatitis B and hepatitis C testing as these cause infection in the baby in utero, at delivery and during breastfeeding.

Weight

Women should maintain their body mass index (BMI) (weight (kg)/height (m)2) between 20 and 25. Women who are underweight may not be able to conceive due to hypothalamic anovulation and putting on weight to maintain their BMI above 18 will usually cause periods and fertility to return. Overweight women (especially if BMI is greater than 30) should be advised to lose weight before pregnancy, as obesity is a major risk factor for pre-eclampsia, gestational diabetes, thrombosis and infection (especially urinary tract infection and wound infection). Obesity is also associated with macrosomia and difficulty in monitoring the growth of the baby. Overweight women who are having difficulty conceiving often have polycystic ovarian syndrome and relatively small amounts of weight loss (1–2 stone or 6–13 kg) will normally restore ovulation.

Exercise

Excessive exercise inhibits hypothalamic function and causes hypothalamic hypogonadotrophic anovulation. Moderate exercise is not harmful in pregnancy and activities such as swimming and walking are recommended. High-impact sports and some racket sports should be avoided from early pregnancy if they are more likely to cause falls and trauma, with a consequent risk to the fetus.

Diet

A healthy diet is low in salt and saturated fat, high in fibre, fresh fruit and vegetables, with more white meat and fish than red meat.

Some foods need to be avoided in pregnancy due to the risk of listeriosis, salmonella and toxoplasmosis. These include:

• Unpasteurized milk and cheese

• Pâté and uncooked or poorly cooked meat

• Shellfish

• Raw eggs.

Women should wash their hands before cooking, and wash fruit and vegetables to reduce the risk of contamination. Liver should not be eaten, as high doses of vitamin A are associated with congenital abnormality.

Vitamins

Folic acid (vitamin B9) reduces the risk of neural tube defects in the fetus by up to 75%. It is advised that 400 μg (available over the counter) should be taken daily from 12 weeks prior to conception until 12 weeks’ gestation. This is increased to 5 mg daily for women on antiepileptic medication and those with a family or previous obstetric history of a neural tube defect. Other vitamin supplements are not needed with a normal diet and excessive vitamin A intake should be avoided.

Medications

Drugs associated with subfertility

Many antipsychotics and antidepressants cause infertility by antagonizing dopamine, thus inducing hyperprolactinaemia and inhibiting ovulation. These may need to be reviewed prior to attempting pregnancy. Newer drugs such as clozapine and olanzapine and serotonin-specific reuptake inhibitors do not have this effect.

Drugs in pregnancy

The National Teratology Information Service and individual drug data sheets give information on harmful effects of drugs in pregnancy. Many common drugs such as paracetamol, penicillins and cephalosporins are safe in pregnancy. Non-steroidal anti-inflammatory drugs should be avoided because of their likely link with miscarriage in the first trimester and oligohydramnios and patent ductus arteriosus later in pregnancy.

Women on warfarin therapy should be converted to heparin, preferably low-molecular-weight, before pregnancy occurs in view of the association between warfarin and congenital abnormality, and this is an important point in prepregnancy counselling. This risk occurs between 6 and 12 weeks’ gestation. However, women with artificial heart valves, in whom the risk of stopping warfarin is very significant, should be seen by the haematologist prior to pregnancy to plan anticoagulation management, weighing the risk of thrombosis and stroke from suboptimal anticoagulation against teratogenicity and fetal or maternal haemorrhage from warfarin.

Antiepileptic medications are associated with congenital malformations and should be reviewed prepregnancy to reduce the number of different drugs, thus reducing the risk to the fetus.

Angiotensin-converting enzyme inhibitors can cause skull defects, oligohydramnios and renal complications in the fetus. Diuretics should be avoided, as they are teratogenic in animal studies. Beta-blockers may cause growth restriction, hypotension and neonatal bradycardia in the fetus and are generally avoided. Calcium channel antagonists, hydralazine and labetalol are not known to be harmful but methyldopa has been used most safely in pregnancy and a plan should be made to convert most women on other hypertensives to methyldopa or labetalol once pregnancy is confirmed.

Rubella

Most women have now been immunized against rubella in childhood, but the antibody level can be checked prepregnancy as some women will have low-level or absent antibodies and should have a further vaccination. Care must be taken to ensure that the woman is not pregnant at the time of administration as the vaccine is live and there is a theoretical risk of infection of the fetus (although no cases of congenital rubella syndrome have been reported from inadvertent vaccination during pregnancy).

Fetal abnormality and genetic disorders

Parents with a family history or previous personal history of a baby with a fetal structural abnormality (e.g. neural tube defect), chromosomal disorder (e.g. trisomy 21) or gene disorder (e.g. muscular dystrophy, cystic fibrosis or haemoglobinopathies) have an increased risk of future pregnancies being affected. Details of prepregnancy and antenatal tests for such conditions should be explained. Prior to pregnancy these may include karyotyping or DNA analysis of both parents, and possibly extended-family members. In pregnancy, early scans and diagnostic tests, such as chorionic villous sampling (CVS) and amniocentesis, are available to diagnose many disorders.

Couples must be allowed to choose the investigations they would like and at what stage. Many parents choose to decline all preconceptual and prenatal testing for fetal abnormality.

For some specific disorders steps may be taken to reduce the chance of a fetus being affected. For example, women with a high risk of neural tube defect in their fetus should take a higher dose of folic acid preconceptually (5 mg daily).

Preimplantation genetic diagnosis

Preimplantation genetic diagnosis is a new technique used for families with serious genetic problems (sex-linked conditions such as Duchenne muscular dystrophy, single-gene disorders such as cystic fibrosis and chromosomal abnormalities). In vitro fertilization is used to produce multiple embryos. These are allowed to develop to the 8-cell stage (day 3) when a cell is removed from each embryo for genetic analysis. Affected embryos can thus be identified and discarded, with only ‘healthy’ embryos transferred back into the uterus.

The technique can only be used where the disorder has been characterized genetically and when it causes significant effects on the child.

Specific medical conditions

Women with the following medical problems should have specialist review of their management prior to pregnancy.

Diabetes

Good glycaemic control significantly reduces the incidence of fetal abnormality. Diabetic retinopathy should be treated before conception to reduce the risk of deterioration with pregnancy. Prepregnancy assessment also allows for screening for nephropathy, which is a strong predictor of pre-eclampsia and worsening renal function in pregnancy. Many units now manage these patients in specialized joint clinics with endocrinology.

Epilepsy

The risk of fetal abnormality increases with the number of different anticonvulsant medications being taken and women considering pregnancy should, therefore, have the number minimized.

All epileptics on medication should also be given 5 mg folic acid daily from 3 months preconception to counteract the folate-antagonist effect of the drugs and thus reduce the chance of a neural tube defect in the fetus. It should also be emphasized that antiepileptic medication should be continued in pregnancy as the threshold for fits is likely to reduce and the risk to the mother of having fits outweighs the teratogenic risk of the medication.

It is worth considering stopping all medication prior to conception if a woman has had no fits for 2 years.

Cardiac disease

Women with severe cardiac disease, specifically Eisenmenger’s syndrome (right-to-left shunt as a result of fixed high pulmonary vascular resistance), pulmonary hypertension from any cause and uncorrected tetralogy of Fallot should be strongly advised not to become pregnant as there is a significant maternal mortality (50% for Eisenmenger’s syndrome). There is also a very high chance of extreme prematurity in the fetus and a high perinatal mortality rate.

Women with moderate- to high-risk cardiac disease such as mitral stenosis, aortic stenosis, Marfan’s syndrome and coarctation of the aorta should all be assessed by a cardiologist before pregnancy. This will allow for assessment of the risk of becoming pregnant and treatment to improve the outcome of pregnancy, such as repair of coarctation or mitral valve surgery.

Low-risk heart diseases such as atrial and ventricular septal defects, patent ductus arteriosus, and mitral or tricuspid valve regurgitation are well tolerated in pregnancy and generally these women do not need prepregnancy assessment.

Hypertension

Women with raised blood pressure should be assessed before pregnancy to rule out any underlying cause for the hypertension such as renal disease, coarctation of the aorta or endocrinological disorders. Their renal function should also be checked as raised creatinine would indicate a higher risk of pre-eclampsia and deterioration of renal function.

Renal disease

Renal disease is likely to be worsened by pregnancy and women with high creatinine levels (greater than 125 μmol/l) are at particular risk. If the creatinine level is above 250 μmol/l then they should consider avoiding pregnancy as up to 50% would develop long-term deterioration of their kidney function.

Women undergoing renal dialysis have impaired fertility and rarely become pregnant. However, they should still be advised to use contraception as pregnancy would be unlikely to have a successful neonatal outcome and would cause major problems in dialysis management. Women who have had a renal transplant, and in whom the renal function is stable, may consider pregnancy 2 years posttransplant, as their likely long-term prognosis is good.

Prenatal diagnosis

Prenatal diagnosis refers to the diagnosis of fetal abnormalities in utero. The abnormalities may be minor or severe. If severe they may not be compatible with life or may be likely to cause long-term serious morbidity or handicap. Some abnormalities may require therapy in utero or a plan made for postnatal management. Screening programmes focus on the commonest chromosomal abnormality, Down’s syndrome (trisomy 21), though both the ultrasound and serum tests often detect other chromosomal and structural abnormalities. There is an important distinction between screening tests and diagnostic tests.

Screening tests

Screening tests give an estimate of risk for that particular pregnancy. Age alone, for example, is a risk factor for Down’s syndrome; in the baby of a woman aged 20 the risk is 1 in 1500, whereas at age 40 it is 1 in 50. Paternal age has no effect on fetal chromosomal abnormality.

Serum screening

The triple test, quadruple test and integrated test use combinations of serum markers (alpha-fetoprotein (AFP), oestriol, human chorionic gonadotrophin beta-subunit, inhibin A and pregnancy-associated plasma protein A) combined with the age of the mother and confirmed gestation of the pregnancy to give a calculated estimate of risk of Down’s syndrome. The tests can usually be performed from 14 to 20 weeks’ gestation and the results are generally available within 2 weeks. The false-positive rate depends on the test but is around 5% and the tests detect 85–90% of babies with Down’s syndrome.

Ultrasound scan

The nuchal translucency test or NT is performed between 11 and 14 weeks’ gestation, when the fetus has a crown–rump length of between 45 and 84 mm. It involves measuring the thickness of the fold of skin over the back of the fetus’ neck and size of the baby and combining this with the mother’s age and gestation of the pregnancy to estimate the risk of Down’s syndrome. A higher risk of Down’s syndrome is found with a greater nuchal translucency. The test detects 85% of babies with Down’s syndrome with a false-positive rate of about 5%. A high NT is also found with many other chromosome abnormalities, especially trisomy 18, 13 and Turner’s syndrome.

In the second trimester, specific ultrasound markers for Down’s syndrome can be identified such as brachycephaly, venticulomegaly, atrial septal defect, duodenal atresia, echogenic bowel, hydronephrosis and short limbs. The risk of Down’s syndrome increases with the number of abnormalities detected.

Combined tests

Some tests use both NT and biochemical markers to calculate a risk of Down’s syndrome.

All of the above tests involve calculation of an estimated risk of Down’s syndrome for that particular fetus. Generally, a positive result is given if the risk is greater than 1 in 250 and those couples are then offered a diagnostic test such as amniocentesis or CVS. Prior to the introduction of serum screening and nuchal translucency, all women over the age of 35 were considered high-risk and offered amniocentesis. Most women over 35 are now reassured by low-risk NT or serum screening test results and therefore avoid unnecessary invasive tests.

Limits of screening tests

Pretest counselling

All women who undergo a screening test should have the test fully explained prior to the procedure. The concept of risk, however, is often poorly understood and, therefore, informed consent can be difficult to obtain.

False positives and unnecessary tests

Both serum screening and nuchal translucency measurement have a false-positive rate of about 5%. This causes anxiety and unnecessary invasive tests. Most women who have a positive screen result will not in fact have an affected fetus.

False-negative results

As the tests are screening rather than diagnostic tests, some Down’s syndrome babies will be born to women with low-risk results.

Ethnicity, diabetes and bleeding in early pregnancy affect the serum marker concentrations, making the test less reliable in some groups.

Twins

Serum screening cannot be used effectively for multiple pregnancies, though nuchal translucency is still possible.

Screening tests to detect other abnormalities

Other than Down’s syndrome, screening tests may suggest a high risk of other abnormalities and indicate referral to a fetal medicine unit for further scans or invasive tests.

AFP

Raised AFP alone, found incidentally at serum screening, is associated with neural tube defects and anterior abdominal wall defects as well as Patau’s syndrome (trisomy 13). In the absence of structural abnormality, increased AFP is associated with intrauterine growth restriction and so regular ultrasound assessment is recommended

Increased NT

In women with a high-risk NT but no chromosomal abnormality, there is an association with multiple abnormalities, including congenital heart disease, exomphalos, diaphragmatic hernia and skeletal defects.

Structural abnormalities

The commoner minor abnormalities found at second-trimester scan include equinovarus (talipes or club foot), cleft lip and palate, renal pelvis dilatation, echogenic foci in the heart and mild hydronephrosis. These cases should all be referred to the fetal medicine unit to confirm the abnormality, look for other associated abnormalities and determine any further prenatal investigation. Depending on the abnormality, postnatal management can be planned, such as surgery for cleft defects, antibiotics for hydronephrosis or physiotherapy for talipes. Major abnormalities such as cardiac defects will involve a multidisciplinary approach and consideration of delivery in a hospital with a specialized neonatal unit.

Diagnostic tests

Diagnostic tests give a couple a definite answer that their baby does or does not have a disorder. They may be performed after a positive Down’s syndrome screening result or may be requested by the woman instead of a screening test. They are also used where the pregnancy is known to be at high risk of a single-gene disorder or chromosomal abnormality other than Down’s syndrome.

Amniocentesis

A fine needle is inserted transabdominally into the uterus under ultrasound control, after local anaesthetic infiltration. A few millilitres of amniotic fluid, which contains desquamated fetal skin cells, is aspirated and cultured. Chromosome analysis is then performed. The result takes about 2 weeks, but polymerase chain reaction techniques are increasingly being used when an urgent result is necessary as it can detect these chromosomal abnormalities within 2–3 days.

The test can be performed from 15 weeks’ gestation and the risk of miscarriage from the procedure is about 1%. Earlier amniocentesis is avoided as it carries a higher risk of miscarriage and talipes.

Chorionic villous sampling

CVS uses ultrasound guidance to take a biopsy from the placenta for analysis. The risk of miscarriage is also about 1%. As CVS is performed at 11–14 weeks, it is often preferred to amniocentesis as the result is known earlier and decisions about termination can be made sooner. However, it has a higher rate of failed culture compared with amniocentesis. In a very small number of cases an inconclusive result is given due to placental mosaicism. In these cases amniocentesis will be needed at 16 weeks. CVS is only performed after 11 weeks as fetal limb abnormalities can occur if performed earlier.

Cordocentesis

Cordocentesis involves aspiration of fetal blood directly from the umbilical cord, again transabdominally under ultrasound control. It is used from 18 weeks, mostly when an in-utero transfusion may be required, such as with haemolytic disease or alloimmune thrombocytopenia. Other uses of cordocentesis include testing the fetus for infection, such as after maternal parvovirus infection, and for the investigation of fetal hydrops. The risk of miscarriage from the procedure is 1–2%.

Ultrasound in pregnancy

All pregnant women should be offered first- and second-trimester scans. The role of each is as follows.

First trimester (10–14 weeks)

• Establish viability: some pregnancies have failed by the time of the first-trimester scan and the diagnosis of missed miscarriage is made if crown–rump length >7 mm with no fetal heart detected. These women should be offered counselling and evacuation of retained products of conception (ERPC).

• Confirm gestation: up to 14 weeks, the estimated due date should be amended if there is more than 7 days’ discrepancy between dates by last menstrual period and by crown–rump length at scan. Beyond 14 weeks, the gestation should be estimated by biparietal diameter or head circumference, and estimated due date corrected if there is more than 14 days’ discrepancy with menstrual dates. Correct dating is very important for planning induction if the woman does not go into spontaneous labour, but dating of pregnancy becomes less accurate with increasing gestation.

• Gross anatomy: major anomalies such as anencephaly, cystic hygroma, bladder outflow obstruction and major anterior abdominal wall defects can be detected at first-trimester scan.

• Multiple pregnancies: multiple pregnancies can be detected and chorionicity and amnionicity are most reliably determined in the first trimester.

Second trimester (18–24 weeks)

• Structural anatomy: the whole fetus should be examined (brain, face, heart, kidneys, abdomen, spine, hands and feet, genitalia, bladder) and referral made to a fetal medicine unit if any abnormalities are detected.

• Fetal growth: very rarely, often associated with pre-eclampsia, early-onset intrauterine growth restriction or oligohydramnios is detected at the second-trimester scan and indicates further follow-up in the fetal medicine department and close monitoring for pre-eclampsia.

• Fetal sex: this can be determined in the second trimester with 99% accuracy if parents wish it, though concerns over the misuse of this information by some cultural groups means that it is not offered in all units.

• Placental site: if the placenta encroaches into the lower segment of the uterus a further scan is arranged for 34 weeks to recheck its location and plan delivery accordingly.

Further scans

Further scans may be arranged for suspected growth restriction or abnormal liquor volume. They may also be needed to follow up any abnormality found at the second-trimester scan. Later in pregnancy ultrasound may also be used to assess fetal well-being by Doppler assessment of blood flow in the umbilical artery and other fetal vessels, or by biophysical profile (breathing movements, gross body movements, fetal tone, heart rate reactivity and amniotic fluid volume).

Other ultrasound screening tests

Fetal echocardiography

All women with a high risk of fetal cardiac abnormalities should be offered a second-trimester fetal echocardiography scan. This includes women with congenital heart disease, diabetes or epilepsy as well as those with a previous child with a congenital cardiac problem. A high-risk NT result and abnormal or inadequate views of the heart at routine second-trimester scan are other indications for fetal echocardiography.

Uterine artery Doppler

Many units use Doppler flow studies to assess the resistance in the maternal uterine arteries. High resistance at 20–24 weeks’ gestation indicates a high chance of pre-eclampsia, abruption and growth restriction, so these women should be offered close blood pressure and fetal growth monitoring.

Cervical length

There is currently great interest in the transvaginal measurement of the cervical length to indicate risk of late miscarriage and extreme prematurity. If the cervix is short then there is some evidence that elective cervical cerclage in high-risk women may prolong the time to delivery.

Antenatal care

Antenatal care aims to optimize the health and well-being of mother and baby, and to detect and treat any abnormal events in pregnancy. The commonest significant disorder diagnosed is pre-eclampsia.

Antenatal care may be provided by the GP, midwife (in hospital or in the community) or the obstetrician team. The commonest is shared care between the midwife and GP, with referral for obstetric input when indicated.

Most women will not need to see an obstetrician unless factors in the booking or during the antenatal period indicate. Indications for referral at booking are shown in Table 11.1.

Table 11.1 Factors at booking indicating referral for obstetric or senior midwifery review

Age over 40 years or under 19 years
Body mass index ≥35 or <18
Grand multiparity (more than six pregnancies)
Conditions such as hypertension, cardiac or renal disease, endocrine, psychiatric or haematological disorders, epilepsy, diabetes, autoimmune diseases, cancer, human immunodeficiency virus (HIV)
Previous caesarean section or other uterine surgery
Previous postpartum haemorrhage
Severe pre-eclampsia or eclampsia
Previous pre-eclampsia or eclampsia
Three or more miscarriages
Previous preterm birth or mid-trimester loss
Previous psychiatric illness or puerperal psychosis
Previous neonatal death or stillbirth
Previous baby with congenital abnormality
Previous small for gestational age (SGA) or large for gestational age (LGA) infant
Family history of genetic disorder

At all visits, the woman should be encouraged to discuss her concerns and any minor disorders of pregnancy, discuss tests and their results, and have her blood pressure and urinalysis checked. In the second trimester growth is assessed by measurement of symphysis–fundal height (SFH) and from 36 weeks, presentation is clinically assessed by palpation. Antenatal visits also provide an opportunity to discuss the forthcoming delivery and the woman’s birth plan.

Women should keep their own obstetric notes, in which all the health professionals involved make their documentation, and all pregnancy results are filed. These are then stored with the main hospital records following delivery.

Women with an uncomplicated first pregnancy would normally be seen 10 times during the pregnancy and parous women who have had previous uncomplicated pregnancies seven times.

Typical timing of antenatal visits, which might be with GP, midwife or obstetrician, for a nulliparous woman are outlined below.

Booking (6–12 weeks)

A medical, gynaecological, obstetric, family and social history should be taken. Drugs and allergies are recorded. Examination should include height and weight, and calculation of BMI. Booking blood pressure must be recorded. Breast or pelvic examination is not indicated and should never be performed in the antenatal setting without a specific indication and informed consent from the woman, with a chaperone present. One such indication for pelvic examination is in a woman with a history of female genital mutilation, who may need early referral to a specialist clinic for antenatal de-infibulation, and a management plan made for delivery.

First-trimester scan should be arranged to confirm dates and screen for Down’s syndrome. If the woman presents after 14 weeks a scan should be arranged to confirm gestation (by biparietal diameter or head circumference) and serum screening for Down’s syndrome offered. Urine should be checked for proteinuria and a midstream urine sample sent to screen for asymptomatic bacteriuria. Booking blood tests should be taken. The woman should be referred to an obstetrician if indicated from the previous history. Information should be given on diet, smoking, alcohol, exercise (see prepregnancy counseling, above) and antenatal care.

Booking blood tests

All the tests should be explained including the reasons why they are being taken and what action might be taken if the results are abnormal:

• Full blood count: to exclude anaemia.

• Group and antibody check: to detect Rhesus-negative women and atypical antibodies.

• Haemoglobinopathy screen: this may be checked in all women or used selectively for those of Afro-Caribbean, Mediterranean or Asian origin. Those with positive results should be offered counselling and partner testing followed by antenatal diagnosis for at-risk fetuses.

• Rubella: to check immunity and plan postnatal vaccination for those with low-level or no immunity. Such women must also be warned about avoiding exposure to the virus.

• Syphilis: to check for syphilis antibodies, which indicate a possibility of current infection in the mother and therefore risk of congenital abnormality in the fetus. Women with a positive result must be referred to a genitourinary medicine (GUM) clinic, though many will be false positives from pregnancy or previously treated disease.

• Hepatitis B: women with positive results should be referred to a gastroenterologist. Neonatal vaccination and immunoglobulin must be planned and interventions such as fetal scalp electrode and fetal blood sampling in labour should be avoided.

• HIV: HIV-positive women should be referred to GUM physicians, offered counselling and given antiviral agents prior to delivery. They should be advised to deliver by caesarean section and avoid breastfeeding.

16 weeks

All results from the booking visit should be given and explained. Anaemia should be treated if necessary. Blood pressure and urine should be checked.

25 weeks

The result of the anomaly scan should be reviewed. Blood pressure and urine should be checked and SFH recorded. Fetal movements should be asked about (usually felt at 18–20 weeks in nulliparous, 16–18 weeks in parous women). Fetal heart beat should be checked with Doppler or Pinnard stethoscope. Antenatal classes should be discussed.

28 weeks

Blood pressure, urine and SFH should be checked. Fetal movements should be asked about and fetal heart auscultated. Repeat screen for anaemia by full blood count, and an antibody screen should be sent (regardless of Rhesus status). Anti-D should be given to Rhesus-negative women.

31 weeks

Blood pressure, urine and SFH should be checked. Fetal movements should be asked about and fetal heart auscultated. Iron should be commenced if haemoglobin is less than 10.5 g/dl.

34 weeks

Blood pressure, urine and SFH should be checked. Fetal movements should be asked about and fetal heart auscultated. A second dose of anti-D should be given to Rhesus-negative women.

36 weeks

Blood pressure, urine and SFH should be checked. Fetal movements should be asked about and fetal heart auscultated. The position of the baby should be assessed clinically and external cephalic version recommended and arranged if breech. If the placenta was low at 20 weeks then the repeat scan should be reviewed for placental site.

38 weeks

Blood pressure, urine and SFH should be checked. Fetal movements should be asked about and fetal heart auscultated. Fetal position should be checked.

40 weeks

Blood pressure, urine and SFH should be checked. Fetal movements should be asked about and fetal heart auscultated. Fetal position should be checked.

41 weeks

Blood pressure, urine and SFH should be checked. Fetal movements should be asked about and fetal heart auscultated. The fetal position should be checked. Membrane sweep should be offered and recommended and a plan made for induction of labour by 42 weeks.

For parous women the 14-, 25- and 31-week visits can be omitted unless specific factors indicate that an extra visit is needed.

Obstetric-led care

Some women will need obstetric-led care and the timing of these visits should be tailored to the specific problem. For example, a diabetic woman may need to be seen by the hospital team every 2 weeks throughout the pregnancy, whereas a woman with a previous caesarean section who plans a vaginal birth in this pregnancy may see the obstetrician once and then be referred back to her midwife for the rest of her antenatal care.

Some women should have antenatal care within a multidisciplinary team. These would include those with diabetes, cardiac or renal disease.

Rhesus disease and other red-cell alloimmune antibodies

All women should have their blood sent for group and antibody screen at booking as 15% are Rhesus-negative (they do not carry the Rhesus D antigen on their red blood cells). These women are, therefore, at risk of developing anti-D antibodies to a Rhesus-positive fetus. This would not usually occur in a first pregnancy unless sensitization had occurred previously, for example from a blood transfusion. Potentially sensitizing events in the pregnancy include:

• Threatened miscarriage, miscarriage, ERPC or ectopic pregnancy

• Trauma to the abdomen, such as amniocentesis, CVS or road traffic accident

• External cephalic version

• Abruption or other antepartum haemorrhage

• Delivery, especially if multiple pregnancy or manual removal of placenta

• Spontaneous fetomaternal haemorrhage.

Haemolytic disease of the fetus involves anaemia and fetal hydrops, which can result in fetal death if not treated by intrauterine blood transfusion.

The rate of sensitization has reduced to 1.5% by the use of anti-D at delivery and at potentially sensitizing events. However, it is estimated that this rate will reduce to 0.3% if routine anti-D prophylaxis is given to all Rhesus-negative women at 28 and 34 weeks as well as at delivery.

A standard dose of 500 IU anti-D antibody should be given by intramuscular injection at 28 weeks and 34 weeks as well as 500 IU within 72 hours of delivery (if the baby is Rhesus-positive), to prevent development of anti-D antibodies in a non-sensitized mother. Many units have not implemented this policy due to cost and, therefore, use the traditional strategy of giving anti-D antenatally after a potentially sensitizing event. In this case a Kleihauer test should be taken before giving the anti-D. This gives an indication of the volume of fetomaternal haemorrhage by estimating the number of fetal cells present in the maternal circulation. If the result is greater than 4 ml then the anti-D dose needs to be increased accordingly, after liaison with the haematologist.

Women who already have anti-D antibodies, whether from previous pregnancy sensitization or from a blood transfusion in the past, should not be given anti-D prophylaxis, but have their anti-D titre monitored every 4 weeks from booking. If the antibody titre increases to 15 IU/ml then fetal anaemia is likely and cordocentesis may be needed to estimate fetal haemoglobin and allow transfusion of the fetus if necessary.

Other antibodies

Other antibodies (often described as ‘atypical’) may be detected at booking and may have an effect for the mother or the fetus.

Effect on the fetus

Apart from Rhesus (D) antibodies, the other common antibodies that cause severe haemolytic disease of the newborn are anti-c and anti-K. Anti-e, -Ce, -Fya, -Jka and Cw only rarely cause fetal haemolysis. Women with any of these antibodies should be followed up in the fetal medicine department as for women with anti-D antibodies.

ABO incompatibility between mother and fetus may cause neonatal jaundice, but rarely causes severe haemolytic disease of the newborn.

Effect on the mother

Atypical antibodies in the maternal blood may make crossmatch difficult, and liaison with a haematologist will determine whether any action needs to be taken around delivery to ensure maternal blood loss is minimized and blood can be available if needed. This may involve correcting any anaemia with antenatal iron supplements or arranging a crossmatch late in the third trimester for long-term storage in case of emergency.

Antenatal education

First-time mothers and their partners should be encouraged to attend antenatal classes. These provide information for couples on pregnancy, childbirth and parenting. Topics include the physical and psychological changes in pregnancy, the stages of labour, analgesia in labour, what can go wrong in labour, breastfeeding, the postnatal period and caring for a newborn baby. Classes are thought to reduce anxiety in parents and provide a social interaction with other parents-to-be, though evidence is lacking over whether there is any effect on birth outcomes.

Seat belts in pregnancy

Pregnant women should be advised to continue to wear seat belts, but to position the lap belt under the gravid abdomen, to minimize the impact to the fetus and placenta if an accident occurs.

Flying in pregnancy

Airline protocols vary on when women can fly in pregnancy and women should always check with their airline what their protocol is. Many airlines will carry women until 34–36 weeks’ gestation, though they may request a letter of confirmation from the obstetrician regarding the pregnancy well-being. This should be provided as long as there are no specific risks. As pregnancy and probably flying both increase the risk of thrombosis, women should avoid sitting for too long, perform regular calf exercises and drink plenty of fluids. For long-haul flights antithrombotic stockings may be prescribed.

Insurance companies also need to be consulted when flying during pregnancy as they may have limited cover, especially for neonatal care in case of premature delivery abroad.

Summary

• Prepregnancy counselling is vital for those with serious medical conditions such as diabetes, epilepsy and cardiac or renal disease to minimize the likely impact of pregnancy on the disease and of the disease (or medication) on the pregnancy.

• Women with high-risk cardiac disease or severe renal disease should be advised not to become pregnant.

• Antenatal screening for Down’s syndrome should be offered early to all pregnant women, with clear counselling regarding screening versus diagnostic tests. The screening tests are also useful in predicting other abnormalities such as cardiac disease.

• Ultrasound in the first trimester will confirm gestation and viability, check for major abnormalities and determine chorionicity in multiple pregnancy.

• Second-trimester ultrasound will check the detailed anatomy of the baby, but also confirm the placental site and growth of the baby.

• Rhesus status must be checked at booking to ensure that Rhesus-negative women are given anti-D either routinely at 28 weeks, 34 weeks and delivery, or after sensitizing events.

• Other important antibodies in haemolytic disease of the newborn are anti-c and anti-K.

• Most women will have normal pregnancies and do not need to see an obstetrician antenatally, but those with obstetric or medical problems must have their care tailored accordingly, often within a multidisciplinary team.

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