Normal pregnancy and antenatal care

Aims and patterns of routine antenatal care

The concept that the reproductive outcomes of a woman might be improved by antenatal supervision is surprisingly recent and was first introduced in Edinburgh in 1911. In many societies, particularly in isolated and low-resource settings, antenatal care either is not available or, for social or religious reasons, is not used when it is available. Unfortunately, it is often least available in those communities where the need is greatest and where antenatal disorders, particularly those linked to malnutrition or over-nutrition, are most common.

The basic assumption is that pregnancy and birth are normal physiological events in which complications may, and do, arise at any stage. Antenatal care aims to detect, prevent or treat these adverse outcomes in order to ensure optimal health of the mother and fetus throughout pregnancy and in the puerperium. It also aims to prepare parents for the transition to parenting and care of the infant.

The ways by which these objectives are achieved will vary according to the initial health and history of the mother and are a combination of screening tests, educational and emotional support and monitoring of fetal growth and maternal health throughout the pregnancy.

In modern antenatal care, the timing of visits, particularly in the first 28 weeks of pregnancy, is closely geared to attendance for screening tests. In uncomplicated pregnancy, a reduction in the number of visits compared to the original suggested schedule of 4 weekly until 28 weeks, 2 weekly until 36 weeks and weekly thereafter has not been shown to adversely affect maternal or perinatal outcome, although maternal satisfaction may be reduced.

Antenatal care is provided through a variety of different mechanisms and may be provided by general practitioners, midwives and obstetricians, often in a pattern of shared care. Pregnancies that are considered to be high risk should receive a high proportion of their care by obstetricians or specialists in fetomaternal medicine. Risk stratification should be assessed at the earliest antenatal visits and care planned accordingly. Guidelines for consultation and referral, such as those produced by the Australian College of Midwives or the National Institute for Health and Clinical Excellence (NICE), can be a useful tool to assess risk and determine the most suitable model of care. Pregnancy risk and the most suitable care provider may alter during the course of pregnancy.

Pre-conceptual care and vitamin supplementation

Ideally, all women would present prior to conception to allow their health care professional to provide them with pre-pregnancy care and counselling. This role is often best provided by the woman’s usual general practitioner. This appointment allows for an opportunity to undertake screening tests and provide advice regarding conception and early pregnancy care. Unfortunately, despite widely available contraception, approximately half of all conceptions are not planned.

Essential components of pre-conceptual care include the assessment of the need for immunization for rubella, varicella and pertussis. If the history of past vaccination or infection is uncertain, serology may be required. If serology is negative or immunization is due, this can then be provided. As these vaccines are live attenuated viral vaccines, it is recommended that the woman use adequate contraception to defer conception for 28 days following administration. Administration of the influenza vaccine on a seasonal basis to women who are intending to be or who are pregnant is also recommended due to the increased incidence of serious morbidity associated with influenza infection in pregnancy. This visit is also an ideal opportunity to undertake routine cervical cancer screening if due.

Dietary and vitamin supplementation advice should also be given at this time. It is recommended that all women take a folic acid supplement (400–500μg daily) for at least 1 month prior to conception and the first 3 months of pregnancy as an effective means of reducing the incidence of neural tube defects. Certain risk groups may be recommended to take a higher dose (5mg daily), such as those on anti-epileptic agents, obese women, diabetic women or women with a past history of neural tube defects. Iodine supplementation of 150μg per day is also recommended in countries or regions where there is a dietary deficiency of iodine to aid in the development of the fetal brain. Consideration of screening for vitamin D deficiency in at-risk populations (including those with darker skin tones or who are always covered while outside) can be considered, with supplementation given if required.

Maternal medical conditions, including medications, can be reviewed and optimized at this time. This provides an opportunity to discuss the impact of pregnancy on the medical condition, as well as the impact of the medical condition on pregnancy. Medication may need to be altered or doses reduced where appropriate. Referral to specialist physician colleagues for treatment optimization may be appropriate.

Optimization of pre-conceptional health with advice on a nutritious diet and regular moderate exercise should also be provided at this time. Exploration and discussion around the use of licit and illicit substances should also be explored.

Changing demographics of pregnancy

Maternal age is an important determinant of outcome in obstetric services, with increased risk being associated with both extremes of maternal age. The median age of women giving birth in developed countries has continued to rise and currently sits at just over 30 years. Fertility rates for women over 40 have trebled since 1990 and now exceed the fertility rate for women under 20 years. Fertility in women under 25 (including amongst adolescent women) is now at the lowest rate since recording began in the UK in 1938. The tendency for women to delay childbearing until later in life is seen consistently across developed countries. The reasons for this are complex and due to a number of social, economic and educational factors. Fertility rates are highest in the 30–34 years age group.

Use of assisted reproductive technologies (ARTs) has increased along with the rise in median birthing age. Approximately 3.6% of babies born are conceptions assisted by ART in Australia and the UK. In addition, rates of multiple pregnancies have plateaued, currently around 1.6% of all mothers. The previous rapidly rising rates were largely due to the increases in ART and increasing maternal age. However, rates of multiples in ART pregnancy are declining due to the increased use of single-embryo transfer. The majority of multiple pregnancies remain due to spontaneous conceptions.

The absolute number of babies born to each woman continues to be low, with 75% of mothers giving birth to their first or second baby. The median age of first-time mothers also continues to rise and is currently around 28 years.

Women are active participants in antenatal care, with over 98% having at least one antenatal visit and 92% having five or more visits. Pre-term birth occurs in around 8.7% of all pregnancies, with more than 80% occurring between 32 and 36 weeks.

Rates of caesarean section as a proportion of births increase with increasing maternal age and with increasing body mass index (BMI).

The booking visit

The details of antenatal history and routine clinical examination are discussed in the preceding chapter. However, certain observations should be obtained at the first visit and it is preferable that these observations be made within the first 10 weeks of pregnancy. The measurement of maternal height and weight is important and has value in prediction of pregnancy outcomes. Women with a low BMI (less than 20, where BMI is estimated as weight (kg) divided by height (m ² )) are at an increased risk of fetal growth restriction and perinatal mortality. Women with a high BMI are recognized as being at increased antenatal, intrapartum and postnatal risk, with the risks beginning to rise from a BMI of 30.

The initial measurement of blood pressure should be taken as early as possible to determine the presence of pre-existing hypertension or as a reference point for hypertension detected at later gestations.

Consideration of past obstetric history, including mode of delivery

A record should be made of all previous pregnancies, including previous miscarriages and terminations, and the duration of gestation in each pregnancy. In particular, it is important to note any previous antenatal complications, details of onset of labour, the duration of labour, the presentation and the method of delivery and the birth weight and gender of each infant. The mode of delivery (spontaneous, assisted or caesarean section) has implications for the current birth and must be explored. Previous operation records should be sought if relevant to aid in appropriate counselling for this pregnancy.

The condition of each infant at birth and the need for care in a special care baby unit should be noted.

Complications of the puerperium, such as postpartum haemorrhage, extensive perineal trauma or wound breakdown, infections of the genital tract, deep vein thrombosis or difficulties with breast-feeding, may all be relevant to the current pregnancy.

Recommended routine screening tests

Beginning at the first visit, a number of screening tests are recommended. Some will be repeated later in the pregnancy. The omission of offering these tests will generally now be considered to be evidence of substandard practice, so they have medicolegal importance as well as clinical relevance. National evidence-based guidelines are available to guide the health care practitioner.

Blood group and antibodies

Blood group should be determined in all pregnant women, and screening for red cell antibodies should be undertaken early in pregnancy. In Rhesus (Rh)-negative women, screening for Rh antibodies should be performed at the first visit (preferably in the first trimester) and then repeated at 28 weeks’ gestation. ABO antibodies may also cause problems in the fetus and newborn, but no method is available to counter this problem.

The use of anti-D immunoglobulin

Around 15% of Caucasian women will be Rh negative and be at risk of developing anti-D antibodies during or immediately following pregnancy. The formation of anti-D antibodies may pose a risk to the wellbeing and even survival of a subsequent fetus due to the pre-formed antibodies crossing the placenta and attacking the red blood cells of an Rh-positive fetus. The effects on the fetus and newborn can be devastating and include fetal anaemia, hydrops, neonatal anaemia, jaundice, kernicterus or fetal death in utero. There is very strong evidence dating from the 1960s that postpartum administration of anti-D immunoglobulin (anti-D Ig) can dramatically reduce the incidence of this complication.

Until the past few years, anti-D Ig was given only to women with a sensitizing event in pregnancy or postnatally to women delivered of an Rh-positive infant. Given within 72 hours of birth, this dose reduces the risk of Rh isoimmunization to around 1.5%. Quantitation of the degree of fetomaternal haemorrhage and the need for further doses should be undertaken by flow cytometry (where available) or the Kleihauer-Betke test prior to administration of the first dose.

Sensitizing events include normal delivery, miscarriage, termination of pregnancy, ectopic pregnancy, invasive prenatal diagnosis, abdominal trauma, antepartum haemorrhage or external cephalic version. Sensitization during pregnancy can also occur without the woman being aware of such an event. Hence, now that anti-D Ig is readily available, it has become standard practice to give anti-D Ig prophylaxis at 28 and 34 weeks’ gestation ( Fig. 7.1 ). This will prevent maternal immunization by an Rh-positive fetus in all but 0.2% of Rh-negative women, in whom the infusion of cells from the fetus overwhelms the dose of antibody administered. This is in addition to the earlier noted indications.