After studying this chapter you should be able to:
Knowledge criteria
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Describe the aims and patterns of routine antenatal care
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List the key elements of preconceptual care
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Discuss the risks of substance abuse in pregnancy
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Contrast the changing demographics of pregnancy
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Discuss the significance of previous obstetric history on planning antenatal care
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List the routine investigations used in antenatal care including screening for fetal abnormality
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Discuss the role of anti-D immunoprophylaxis
Clinical competencies
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Carry out a routine antenatal booking visit
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Provide antenatal education on diet and exercise in pregnancy
Professional skills and attitudes
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Consider the importance of the interaction between social and cultural factors and pregnancy
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Consider principles of safe prescribing in pregnancy
Aims and patterns of routine antenatal care
The concept that the general wellbeing and reproductive performance of a woman might be improved by antenatal supervision is surprisingly recent, and was first introduced in Edinburgh in 1911. In many societies, antenatal care 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 aims of antenatal care are:
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To ensure optimal health of the mother throughout pregnancy and in the puerperium.
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To detect and treat disorders arising during pregnancy that relate to the welfare of both the mother and the fetus and to ensure that the pregnancy results in a healthy mother and a healthy infant.
The frequency of antenatal visits was first established by a group of providers of antenatal care in 1929. The protocol advised that antenatal visits should occur monthly from 8 weeks gestation until 28 weeks and then every 2 weeks until 36 weeks and thereafter weekly until the time of delivery. In modern antenatal care, the timing of visits, particularly in the first 28 weeks of pregnancy, is now more closely geared to attendance for screening tests. In uncomplicated pregnancy, a reduction in the number of visits 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 by 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.
Preconceptual care and vitamin supplementation
Ideally, all women would present prior to conception to allow their health care professional to provide them with prepregnancy 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.
Essential components of preconceptual 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 cytology (Papanicolou smear) 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 µg daily) for at least one month prior to conception and the first three 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 (5 mg 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 150 µg 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. Some countries have overcome the problem by using iodized salts for cooking.
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 preconceptional 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.
The risk of substance abuse in pregnancy
Smoking
Smoking has an adverse effect on fetal growth and development and is therefore contraindicated in pregnancy. The mechanisms for these effects are as follows ( Fig. 7.1 ):
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The effect of carbon monoxide on the fetus . Carbon monoxide has an affinity for haemoglobin 200 times greater than oxygen. Fresh air contains up to 0.5 ppm of carbon monoxide, but in cigarette smoke values as high as 60 000 ppm may be detected. Carbon monoxide shifts the oxygen dissociation curve to the left in both fetal and maternal haemoglobin. Maternal carbon monoxide saturation may rise to 8% in the mother and 7% in the fetus, so that there is specific interference with oxygen transfer.
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The effect of nicotine on the uteroplacental vasculature as a vasoconstrictor . Animal studies on the effect of infusions of nicotine on cardiac output have shown that high-dose infusions produce a fall in cardiac output and uteroplacental blood flow. However, at levels up to five times greater than those seen in smokers there are no measurable effects and it is therefore unlikely that nicotine exerts any adverse effects by reducing uteroplacental blood flow.
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The effect of smoking on placental structure . Some changes are seen in the placental morphology. The trophoblastic basement membrane shows irregular thickening and some of the fetal capillaries show reduced calibre. These changes are not consistent or gross and are not associated with any gross reduction in placental size. The morphological changes have not been demonstrated in those women subjected to passive smoking.
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The effect on perinatal mortality . Smoking during pregnancy reduces the birth weight of the infant and also reduces the crown–heel length. Perinatal mortality is increased as a direct effect of smoking and this risk has been quantified at 20% for those women who smoke up to 20 cigarettes per day and 35% in excess of one packet per day. Mothers should be advised to stop smoking during pregnancy.
Paradoxically, there is a considerable volume of evidence to show that women who smoke in pregnancy have a substantially reduced chance of developing pre-eclampsia. However, if they do develop pre-eclampsia, there is a significantly increased risk of perinatal loss.
Alcohol intake
Excessive alcohol intake (in excess of eight standard drinks per day) is associated with a specific syndrome known as the fetal alcohol syndrome. Features in the infant include growth retardation, various structural defects and, in particular, facial defects, multiple joint anomalies and cardiac defects. However, these problems arise in women who consume 80 g of alcohol/day and who will almost inevitably have an unsatisfactory dietary intake as well. This is equivalent to an intake of 8 units/day, where 1 unit is equivalent to one glass of wine (200 mL) or half a pint of beer or lager. Increasingly, there is awareness of fetal alcohol spectrum disorder, a range of neurodevelopmental and behavioural effects attributable to alcohol consumption in pregnancy in a dose-dependent manner. Research is not clear as to what level of alcohol consumption is safe in pregnancy, so a recommendation to abstain from any consumption is the safest choice. In reality, the responsibility lies with the woman to adopt a reasonable approach to her alcohol intake. There is no evidence that the occasional social glass of wine or beer has any detrimental effect.
Illicit drug use
The common forms of drug abuse that occur during pregnancy are from heroin, amphetamines, cocaine and marijuana. All of these drugs have adverse effects on both the mother and the fetus, but many of the adverse effects are related to lifestyle and malnutrition.
Heroin addiction is associated with an increased incidence of intrauterine growth restriction, perinatal death and preterm labour. Furthermore, about 50% of infants exposed to heroin will suffer from neonatal withdrawal manifestations. The mother should be screened for HIV, syphilis, chlamydia and gonorrhoea and should be referred to a drug dependence unit for withdrawal of heroin and replacement with methadone or buprenorphine.
Amphetamine use has become an increasing problem over the past decade. Use in pregnancy is associated with an increased risk of miscarriage, preterm birth, growth restriction, placental abruption, fetal death in utero and developmental anomalies. Referral to a drug dependency service for advice on cessation is recommended.
Cocaine usage may induce cardiac arrhythmias and central nervous system damage in mothers as well as placental abruption, fetal growth restriction and preterm labour. Management of cocaine addiction is directed at withdrawing the drug.
Marijuana has no apparent adverse effect on pregnancy although the active ingredient of 9-tetrahydrocannabinol has been shown to have teratogenic effects in animal studies. Consumption is usually associated with significant tobacco use, which has major detrimental effects as outlined above.
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. In recent years the median age of women giving birth in developed countries has continued to rise, and currently sits at around 30 years. The reasons for this are complex and due to a number of social, economic, and educational factors. Rates of pregnancy in the over 35 age group continue to rise (currently 23% of all births) as does that of women over 40 (4% of all births), however the number of mothers over 45 years remains low.
Access to assisted reproductive technologies (ART) has increased with a subsequent influence on median maternal age. Approximately 3.2% of babies born are conceptions assisted by ART in Australia and the UK. In addition, rates of multiple pregnancies continue to rise, currently around 1.6% of all mothers. This is largely due to the increases in ART and increasing maternal age. Rates of multiples in ART pregnancy are around 10% of all successful conceptions.
Rates of teenage pregnancy continue to decline and sit at around 4% of all births.
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 climb, 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 5 or more visits. Preterm birth occurs in around 7.5% of all pregnancies, with most of these occurring in gestations greater than 32 weeks.
Around 75% of all women use analgesia in labour, most commonly nitrous oxide, followed by opioids, then regional techniques (predominantly epidural anaesthesia, around 30%). Rates in first time mothers of analgesic use are around 85%. Rates of caesarean section as a proportion of births increase with increasing maternal age.
The booking visit
The details of antenatal history and routine clinical examinations are discussed in Chapter 6 . However, certain observations should be stressed at the first visit and it is preferable that these observations should 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 body mass index (BMI; less than 20, where BMI is estimated as weight (kg) divided by height (m 2 )) are at increased risk of fetal growth restriction and perinatal mortality. Women with a high BMI are increasingly recognized as being at increased antenatal and intrapartum risk, with the risks beginning to rise from a BMI of 30.
The initial measurement of blood pressure should be taken as soon as possible as this may provide evidence that, if there is hypertension, it is likely to have predated the pregnancy.
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 induction of labour, the duration of labour, the presentation and the method of delivery, as well as the birth weight and gender of each infant. The mode of delivery (spontaneous, assisted or caesarean section) has implications for the current birth and needs to 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 breastfeeding may all be relevant to the current pregnancy.
Recommended routine screening tests
Beginning at the first visit, a number of screening tests are introduced. Some will be repeated later in the pregnancy. The omission of these tests will generally now be considered to be evidence of substandard practice so they have medicolegal importance as well as clinical relevance.
Haematological investigations
Anaemia is a common disorder in pregnancy and in most communities will be due to iron deficiency, either because of the depletion of iron stores or because of reduced iron intake. Over 90% of pathological anaemia in pregnancy is due to iron deficiency. However, it may also be macrocytic and due to folate or vitamin B12 deficiency or may be related to various parasitic infections.
Haemoglobin concentration and a full blood count should therefore be performed at the first visit and repeated at 28 and 34 weeks gestation. Women who have deficient iron intakes should be given oral supplements of iron from early in pregnancy. Screening for haemoglobinopathies should be routinely offered to those racial groups where conditions such as thalassaemia and sickle cell disease are common.
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 least at 28 weeks gestation. ABO antibodies may also cause problems in the fetus and newborn, but there is no method 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 preformed antibodies crossing the placenta and attacking the red blood cells of a Rh-positive fetus. The effects on the fetus and newborn can be devastating and include 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 a 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.
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. 7.2 ). This will prevent maternal immunization by a Rh-positive fetus in all but 0.2% Rh-negative women, in whom the infusion of cells from the fetus overwhelms the dose of antibody administered. This is in addition to the above indications.
