30
Antenatal care
Introduction
Most pregnancies are uneventful and uncomplicated and would progress normally without medical intervention. There are three main purposes to antenatal care: health promotion, preparation for labour and parenthood and surveillance of risk. The purpose of the latter is to provide appropriate surveillance for all pregnancies in the hope of identifying the small number that develop complications, with the aim of optimizing the outcomes for both the mother and her baby.
This should be achieved without unnecessary interference and tailored to the individual woman. Care is often based on a traditional arrangement of antenatal visits. The schedule varies, with the initial, or ‘booking’ visit, ideally between 8 and 10 weeks, with subsequent visits 4-weekly until 30 weeks; 2-weekly until 32 weeks and then weekly thereafter. There is debate about rearranging this care according to evidence-based practice, which indicates a less frequent attendance; the incentive for change from parents and care providers is often weak.
In western societies, antenatal care is provided by a variable combination of midwives, obstetricians and family doctors, depending on local preferences and resources. Care may be shared and may include some hospital visits and some more local visits to other practitioners, allowing the hospital to focus on those who need more intensive input. Some women will receive their antenatal care solely at home.
In the resource-poor countries, many mothers have little or no antenatal care. Access to healthcare is limited by poverty, lack of facilities, lack of education and cultural resistance.
The booking visit
The purpose of the antenatal booking visit is to detect any risk factors that may indicate the necessity of extra surveillance above that provided to ‘low-risk’ women. It is also an opportunity to identify any social difficulties and to discuss the parents’ own wishes for the pregnancy and delivery.
Past obstetric history
A detailed account of the previous pregnancies and labours should be obtained, including gestation at delivery and whether the labour was induced or of spontaneous onset. The duration of labour, mode of delivery, birth weight, sex, neonatal outcome and any postnatal complications should also be noted.
Women who have experienced obstetric difficulties in a previous pregnancy are often keen to talk these through and consider the likelihood of recurrence. This is frequently a listening exercise so that anxieties can be expressed, especially in cases of previous fetal or neonatal loss. An explanation followed by discussion of possible recurrence risks and a plan for the next pregnancy is useful.
Medical and surgical history
This should include details of previous operations, particularly gynaecological procedures, such as a previous excisional treatment to the cervix (may predispose to cervical incompetence), and include a history of whether blood transfusions have been received (possibility of having developed red cell antibodies). Questions should be asked about relevant medical disorders such as hypertension, diabetes, heart disease, renal disease, epilepsy, asthma or abnormal thyroid function.
Family history
The family history should enquire of potential inherited conditions such as thalassaemia, cystic fibrosis, sickle cell anaemia and also chromosomal disorders and previous congenital structural abnormalities.
History of present pregnancy
The date of the first day of the last menstrual period and details of the menstrual cycle prior to conception should be noted. However, the expected due date is routinely calculated from gestational age assessment following ultrasound in the first half of pregnancy rather than from menstrual dates.
Social and drug history
It is essential to note all drugs and medications taken by the mother immediately prior to and during the pregnancy, as some preparations may be teratogenic. Alcohol, smoking and drug misuse should also be noted and discussed, with referral to appropriate support and/or cessation services. Evidence of socioeconomic deprivation is relevant, since women may require additional support during pregnancy. Identification of matters relating to child protection concerns necessitates referral to the social work department.
Mental health
It is important not to overlook depression or other mental health disorders. A history should be obtained of any previous mental illness, such as schizophrenia, bipolar disorder or any previous postnatal depression or psychosis. A relevant family history or history of previous contact with mental healthcare services should be obtained. Depression should also be considered antenatally and questions can be asked at booking to identify possible depression. Appropriate referral to specialist antenatal support services can then be arranged to support the woman during her pregnancy.
Examination
A general examination is performed to include measurement of pulse rate, blood pressure, weight and height, the latter two used to calculate the body mass index (BMI). A BMI > 30 indicates an increased potential for pregnancy complications. Abdominal examination provides an approximate indication of the uterine size, and may rarely identify abnormal masses and other abnormalities. Vaginal examination is not routinely performed.
Ultrasound scan
This key investigation establishes fetal viability, gestational age and identifies multiple pregnancy when present. It is also an opportunity to measure the nuchal translucency (see p. 266) where appropriate and to diagnose some fetal anomalies, e.g. anencephaly.
Urine analysis
The urine is analysed for the presence of protein and glucose. In early pregnancy, proteinuria may be a sign of a urinary tract infection and glycosuria occasionally indicates hyperglycaemia.
Booking blood samples
Full blood count to exclude maternal anaemia and thrombocytopenia (p. 222).
Blood group to determine the ABO and rhesus status of the mother and to detect the presence of any red cell antibodies (p. 315).
Rubella status to identify those mothers who are not immune to rubella and are therefore at risk of a primary rubella infection during pregnancy. Such women are offered rubella vaccination after delivery (p. 274).
Haemoglobin electrophoresis may be offered to all women, or restricted to those of certain ethnic origin, particularly those of Asian, Afro-Caribbean or Mediterranean origin, and will identify those mothers who may be carriers of sickle cell anaemia or thalassaemia.
Hepatitis B status allows for counselling of the woman and her family together with neonatal vaccination if the result is positive.
Serological testing for syphilis. Those with positive tests should receive referral to a genitourinary medicine specialist and treatment with penicillin where appropriate.
HIV (see p. 188).
Screening discussion
It is essential to use the booking visit to discuss screening options for chromosomal and structural abnormalities. This is often an emotive area and parents should be made aware of the implications of any tests they accept or decline (see p. 266).
Nutritional supplements
All pregnant women should be offered folic acid for the first 12 weeks of pregnancy, as it reduces the risk of neural tube defects. Ideally, folic acid should be provided pre-conceptually. Vitamin D deficiency is becoming more common among pregnant women, giving rise to skeletal abnormalities such as rickets, in newborns. Women who are at risk of vitamin D deficiency include those who remain covered while outdoors; eat a diet low in vitamin D; have a BMI > 30 or are of South Asian, African, Caribbean or Middle Eastern origin. Appropriate vitamin D supplementation should be offered to these women during pregnancy. Routine iron supplementation is not required and should be reserved for specific indications, principally iron deficiency anaemia.
Health promotion
The antenatal period provides an ideal opportunity to provide health promotion information to women who might otherwise not interact with health services. Information should be provided in an accessible format and interpreter provision should be available as required. It is important to be mindful of cultural issues and to deal with these sensitively. For example, women who have undergone female genital mutilation (FGM) may be reluctant to discuss this with a healthcare professional. However, by doing so, a plan of care can be discussed in preparation for birth.
Antenatal planning
Mothers at the extremes of reproductive age are at increased risk of obstetric complications, particularly hypertensive disorders, and they also have an increased risk of perinatal mortality.
The incidence of pre-eclampsia in a second pregnancy is 10–15 times greater if there was pre-eclampsia in the first pregnancy, compared with those with a normal first pregnancy, although pre-eclampsia tends to be less severe in subsequent pregnancies. Low-dose aspirin (75 mg once daily) taken from the first trimester and continued throughout pregnancy reduces the likelihood of recurrent pre-eclampsia.
Those who have had a previous instrumental delivery usually have an unassisted delivery next time around, but may occasionally request a planned caesarean section. Careful consideration of the advantages and disadvantages of such a request is required. In general, women with a previous caesarean section for a non-recurrent indication (the majority), e.g. breech, fetal distress or relative cephalopelvic disproportion secondary to fetal malposition should be offered vaginal birth after caesarean (VBAC), although repeat elective caesarean section may be recommended in certain circumstances. With spontaneous onset of labour, women can be quoted an approximate 70% likelihood of achieving a vaginal birth when undertaking VBAC, with the principal risk of uterine rupture occurring in approximately 1 in 300. Women with uncomplicated pregnancies should be given information on different birth settings, including home, from which they can choose their preferred place of birth.
In situations where there has been previous fetal growth restriction or an intrauterine death (death of the fetus in utero after 24 weeks’ gestation), subsequent management depends on the cause and the estimated likelihood of recurrence. More intensive antenatal monitoring is usually offered and the outcome is usually good, particularly when the loss was ‘unexplained’.
Smoking during pregnancy is associated with fetal growth restriction and premature delivery. Smoking is also associated with an increased risk of placental abruption, intrauterine death and sudden infant death syndrome. Alcohol and illicit drug misuse, e.g. cocaine, carry significant fetal risks and these should be avoided in pregnancy.
Women whose work environment exposes them to radiation, hazardous gases or specific chemicals should be appropriately counselled. There is no evidence that video display units (VDUs) are harmful, or indeed that working during pregnancy itself is harmful to the mother or fetus. Moderate exercise is likely to be of benefit and should be encouraged, but common sense should be applied and exercise be avoided if there are significant complications such as hypertension, cardiorespiratory compromise, antepartum haemorrhage or threatened pre-term labour.
Antenatal surveillance
Subsequent visits are then used to identify obstetric complications; antenatal care is in the most part an exercise in screening both the mother and fetus.
Gestational hypertension and pre-eclampsia
Blood pressure is measured and a urinalysis performed at each visit, and there should be a low threshold for acting on any abnormalities (see Chapter 36).
Fetal growth restriction (FGR) and small-for-gestational-age (SGA)
‘Small-for-gestational-age’ (see also Chapter 35) describes the fetus or baby whose estimated fetal weight or birth weight, respectively is below the tenth centile for its gestation, expressed in weeks. The term ‘fetal growth restriction’ describes ‘a fetus which fails to reach its genetic growth potential’. In practice, it may be difficult to differentiate the two antenatally, but fetal growth restriction carries a significant risk of antenatal and intrapartum asphyxia, intrauterine death, neonatal hypoglycaemia, long-term neurological impairment and perinatal death. It is therefore important to identify these fetuses at an early stage to enable more intensive monitoring or expedite delivery.
Screening for SGA is by clinical palpation and objective measurement of symphysis fundal height (SFH) with a tape measure; this identifies 40–50% of the babies that are SGA. It is recommended that symphysis fundal height should be measured every visit from 24 weeks onwards. Ultrasound fetal biometry is the diagnostic test for the SGA fetus. Routine screening of all pregnancies by third trimester ultrasound is not supported by currently published evidence.
