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.

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