Practical practice points

Introduction

Cardiac disease remains the leading cause of maternal death in the United Kingdom. The major causes of cardiac disease cited in the last report (in 2011) from the Centre for Maternal and Child Enquiries (CMACE) Confidential Enquiry into Maternal Deaths included myocardial infarction, dissection of the thoracic aorta, and cardiomyopathy (most commonly peripartum).[1] Congenital heart disease (CHD) occurs in approximately 0.8% of newborn infants worldwide. Advances in medical and surgical treatments over the past few decades has led to >85% of these infants surviving to adulthood.[2] CHD is associated with increased fetal complications such as fetal loss, fetal growth restriction (FGR), and premature delivery, and an increased risk of fetal CHD. The two main determinants of fetal prognosis are the maternal functional class and degree of cyanosis. If the mother is in New York Heart Association (NYHA) functional class III or IV (see Table 10.1) or has a high-risk disease such as severe aortic stenosis or Eisenmenger syndrome, then pregnancy is associated with high maternal and fetal mortality and morbidity risks (see Table 10.2). Fetal monitoring is therefore a priority. For women with cyanotic heart disease, regular assessment of fetal growth is mandatory because growth can often slow and cease before term. The use of midtrimester uterine artery Doppler as a screening test for the prediction of uteroplacental insufficiency may be valuable for identifying fetuses at risk of intrauterine growth restriction (IUGR) and perinatal death.[3]

Maternal risk factors

Hemodynamic changes during pregnancy can exacerbate the problems associated with CHD, resulting in cardiovascular complications in the mother that may have fetal implications.[4] The outcome is influenced by several factors: functional class (NYHA classification),[5] the nature of the disease, and previous cardiac surgery.

Heart conditions that are likely to give rise to problems include pulmonary hypertension (PH), cyanosis, and severe left ventricular outflow tract obstruction. Siu et al. examined the outcomes of 221 women with heart disease.[6] Poor maternal exercise tolerance (functional class) or cyanosis, myocardial dysfunction, left heart obstruction, prior arrhythmia, and prior cardiac events were predictive of maternal cardiac complications. These predictors were incorporated into a points score to estimate the probability of a cardiac complication in the mother. The rate of cardiac complications for a woman with 0, 1, or >1 of the above factors was 3%, 30%, or 66%, respectively. Neonatal complications occurred in 17% (n=42) of completed pregnancies. Neonatal events included death (n=2), respiratory distress syndrome (n=16), intraventricular hemorrhage (n=2), premature birth (n=35), and small for gestational age (SGA) birthweight (n=14). Poor maternal functional class or cyanosis was predictive of neonatal events.[6]

Pulmonary hypertension

PH is the most hazardous cardiac condition for a pregnant woman and can be an indication for termination of pregnancy to avoid maternal mortality. Severe pulmonary vascular disease whether with (in Eisenmenger syndrome) or without septal defects carries a high risk of maternal mortality, with a rate of about 25%. A 2012 review of 12 pregnancies in 9 women with PH showed that maternal and fetal outcomes for women are improving but the risk of maternal mortality remains significant. In that series, there were two maternal deaths: one related to preeclampsia and one to arrhythmia.[7] PH is poorly tolerated in pregnancy because of the insufficient ability of the right heart to adapt to increases in cardiac output, in association with a poorly compliant pulmonary vasculature. If chronic maternal hypoxia results, it can lead to FGR.

Severe left ventricular outflow tract obstruction

A fixed outflow tract resistance, such as aortic valvular or subaortic stenosis or coarctation of the aorta, may not accommodate the increased cardiac output caused by increased plasma volume. This can lead to heart failure, with a rise in left ventricular and pulmonary capillary pressures, low cardiac output, and pulmonary congestion.

Maternal indices

Whittemore et al. showed that a maternal hematocrit of >44% is associated with an increase in birthweights below the 50th centile, and the live birth rate falls to 8% if the maternal hemoglobin is >20 g/dl. If the maternal oxygen saturation falls below 85%, it is predictive of poor pregnancy outcome, with a 12% live birth rate (Table 10.3).[8]

Another series reported by Presbitero et al. examined 1238 women with CHD in London and Italy.[9] The incidence of maternal cardiovascular complications was high (32%) and included one death from endocarditis 2 months after delivery. Of 96 pregnancies, 43% resulted in a live birth, 37% (n=15) of which were premature. There were 49 spontaneous miscarriages at between 6 weeks and 5 months of gestation and 6 stillbirths at 26–38 weeks. The mean birthweight at term was 2575 g (range 2100–3600 g). The basic maternal cardiac abnormality also influences fetal outcome. Women with single ventricles, tricuspid atresia, tetralogy of Fallot, or pulmonary atresia were found to have a worse pregnancy prognosis compared with those with, for example, Ebstein anomaly with an atrial septal defect, corrected transposition of the great arteries, a ventricular septal defect, or pulmonary stenosis.

Cyanotic vs acyanotic heart disease

The fetal and maternal outcome for pregnant women with acyanotic heart disease is more favorable. Chia et al. retrospectively examined 19 151 deliveries with 143 cases of acyanotic heart disease.[10] The study found no significant difference in the rate of induction, use of epidurals, or operative deliveries between the acyanotic heart disease group and the group without heart disease. Perinatal mortality rates were not significantly different in the two groups (15.3 per 1000 vs 14 per 1000).

Conversely, cyanotic CHD is associated with reduced fertility as well as increased fetal loss. This is because cyanosis worsens owing to increased intracardiac right to left shunting as peripheral vascular resistance falls. For example, the right to left shunt in Eisenmenger syndrome, which occurs as a result of a fixed and high pulmonary vascular resistance, increases during pregnancy. Thromboembolic risk is increased owing to erythrocytosis secondary to hypoxemia. Maternal cyanosis is poorly tolerated by the fetus and is associated with a high incidence of fetal loss (28%), stillbirths, FGR (30%), and preterm delivery (55%), both iatrogenic and spontaneous.[11] This is especially true if oxygen saturation falls below 80–85%.

Sawhney et al. compared 251 pregnancies in women with acyanotic heart disease with 24 pregnancies in women with cyanotic heart disease.[12] The incidences of miscarriage (8.3%), stillbirth (0.8%), and SGA babies (36.4%) were higher in women with cyanotic heart disease than in those with acyanotic heart disease (stillbirth 0.8%, SGA 6.9%).

Cyanotic conditions that have been surgically repaired are not associated with an increased risk to either mother or fetus. Cardiac surgery improves perinatal outcome in women with cyanotic heart disease. A recent review of women with surgically corrected tetralogy of Fallot showed that pregnancy is well tolerated, generally with a good neonatal outcome. However, the risk of congenital cardiac disease in the offspring is increased.[13] Whittemore et al. observed that live births occurred in only 42% of pregnancies with unrelieved cyanosis, but in 72% with palliative shunts and in 78% with surgical repair.[8] These data were reported in 1982 and should thus be interpreted with caution because there have since been major advances in the treatment of CHD.

There are about 100 new Fontan repairs performed each year in the UK. This is a form of surgical palliation for patients who have only one effective ventricular chamber. It involves directly connecting the systemic venous return to the pulmonary arteries, although the precise method of doing this has varied over the last 20 years. While it is likely that not all of these patients will reach reproductive age in 10–20 years’ time, and half are men, they clearly represent a relatively small but important group of women at high risk during pregnancy. Pregnancy carries additional risk owing to the increased hemodynamic burden on the Fontan circulation itself and the single ventricular chamber. It is associated with a 2% risk of maternal mortality. Spontaneous miscarriage is frequent and occurs in up to 40% of pregnancies, probably as a result of congestion of the intrauterine veins. Women with a successful Fontan repair with a small right atrium or total cavopulmonary connection and in NYHA class I or II can probably complete pregnancy, with a successful live birth rate of 45%, if not more.[14]

Valvar heart disease

Regurgitant valvular disease is much better tolerated than stenotic. Mitral stenosis is associated with 10% maternal mortality, which increases to 50% when patients are in NYHA class III or IV; fetal mortality is accordingly high (12–31%). This is because a gradient develops between the left atrium and ventricle and the resultant increase in left atrial pressure can cause pulmonary edema, a rise in pulmonary arterial and right ventricular pressures, and eventually right ventricular dysfunction and failure. Surgical commissurotomy or, nowadays, balloon mitral valvotomy has been performed for severe mitral stenosis (mostly in the second trimester of pregnancy) with marked symptomatic relief and good maternal and fetal outcomes. However, mitral valve surgery, in particular, should be reserved only for selected women (see Chapter 8).[15]

Hameed et al. reported a significantly increased preterm delivery rate (23% vs 6%; p=0.03) and FGR (21% vs 0%; p<0.0001) in women with valvular heart disease.[15]

Malhotra et al. carried out a retrospective comparison of the maternal and fetal pregnancy outcomes of 312 women with valvular heart disease and 321 healthy women.[16] Women with valvular heart disease had a significantly higher incidence of surgical intervention during pregnancy (13.4%), congestive heart failure (5.1% vs 0%, p<0.001), and mortality (0.64% vs 0%). There was also an increased rate of preterm delivery (48.3% vs 20.5%), reduced birthweight (2434 g [standard deviation (SD) 599 g] vs 2653 g [SD 542 g], p<0.001) and a higher incidence of Apgar (appearance (color), pulse rate, grimace response (reflex irritability), activity, respiratory effort) scores of <8 (8.3% vs 4.0%, p<0.001).

Recurrence risk

The overall risk of the fetus having a congenital heart defect is higher if the mother (3–5%) rather than the father (2%) has CHD.[17] The level of risk is dependent on the specific lesion and is higher for outflow tract lesions (Table 10.4).[18,19] If the fetus is affected, the same or a related lesion is the most likely. In women with an atrial septal defect, the risk of an atrial septal defect in the fetus is about 5%; for aortic stenosis, the risk is higher at about 10%.[19] Both Marfan syndrome and hypertrophic cardiomyopathy (or long QT syndrome) carry an autosomal dominant inheritance pattern (50% recurrence risk).[20]

Fetal surveillance

Early ultrasound examination is essential to confirm the gestational age. Increased fetal nuchal translucency (NT) is a common phenotypic expression of trisomy 21 and other chromosomal abnormalities,[21–23] but is also associated with fetal death and a wide range of fetal malformations, deformations, dysgeneses, and genetic syndromes. There is an association between increased NT and cardiac defects in both chromosomally abnormal and normal fetuses.[24] A meta-analysis of screening studies reported that the detection rate of CHD was about 23% in chromosomally normal fetuses, with an increased NT of >3.5 mm, and even higher at 59% in babies with chromosomal abnormalities.[25,26]

The prevalence of major cardiac defects increases exponentially with fetal NT thickness, from 4.9 per 1000 in fetuses with an NT below the median to 35.2, 64.4, and 126.7 per 1000 for NTs of 3.5–4.4 mm, 4.5–5.4 mm, and ≥5.5 mm, respectively. There was no obvious difference in the distribution of NT thickness between the various types of cardiac defect.[27] In the low-risk population, a normal NT is associated with a twofold lower than average risk of congenital heart defects.[24] On the other hand, fetuses with an increased NT, especially those above the 99th centile, are at a high risk of cardiac defects and therefore should not wait until 20 weeks of gestation for specialist echocardiography. With improvements in ultrasound technology, it is now possible to undertake a detailed cardiac assessment by 14 weeks.[28]

Maiz et al. examined the role of ductus venosus blood flow in screening for major cardiac defects in chromosomally normal fetuses with an increased NT at 11 plus 0 weeks to 13 plus 6 weeks of gestation.[29] In chromosomally normal fetuses with increased NT, the finding of an absent or reversed A-wave in the ductus venosus was associated with a threefold increase in the likelihood of a major cardiac defect, whereas the finding of normal ductal flow was associated with a halving of the risk of such defects.

Another large study population of euploid fetuses included 85 cases with major cardiac defects and 40 905 with no cardiac defects. The presence of tricuspid regurgitation was seen in 33% of fetuses with cardiac defects vs 1.3% of those without cardiac defects.[30]

The combination of increased nuchal translucency above the 95th percentile, tricuspid regurgitation, or ductus venosus reversed A-wave can provide an effective screening strategy in the prediction of major cardiac defects in early pregnancy.

Women with CHD are at an increased risk of having offspring with congenital heart defects; therefore, these women should be offered specialist fetal echocardiography between 18 and 22 weeks when visualization of the heart and outflow tracts is optimal. Echocardiography has been successfully applied to the prenatal assessment of fetal cardiac function and structure, and in specialist centers leads to the detection and diagnosis of most cardiac abnormalities. Cardiac anatomy and function, arterial and venous flow, and rhythm should be evaluated. Studies from these specialist centers report the accurate diagnosis of over 90% of defects. However, the majority of such studies refer to the prenatal diagnosis of moderate to major defects in high-risk populations. An acceptable sensitivity in low-risk pregnancies is achieved by correct examination of the four-chamber view at the routine 20 week scan because screening studies have reported a detection rate of about 60% for major cardiac defects. Therefore, in high-risk groups such as those with congenital cardiac defects in one parent or in previous pregnancies, maternal diabetes, or ingestion of teratogenic drugs, detailed fetal echocardiography should be carried out at specialist centers.

Where there is a suspected cardiac defect, referral to a specialist center is essential to obtain the correct diagnosis and for optimum counseling of the parents. Extracardiac anomaly and abnormal karyotype should be excluded by a fetal medicine unit, especially if the heart defect detected has a known association with chromosomal anomalies, such as an atrioventricular septal defect with trisomy 21, or common arterial trunk or interrupted aortic arch with a microdeletion of chromosome 22q11.

In the last decade, there has been a shift in screening for aneuploidies to the first trimester, and extensive research has concentrated on early screening and detection of CHDs. A review of the accuracy of first-trimester ultrasound for detecting major CHD shows a sensitivity and specificity of 85% and 99%, respectively.[31] However, early detailed assessment of the fetal heart requires a high level of expertise in early anomaly scanning and fetal echocardiography.[32] Such early diagnosis of major CHD in the fetus allows the option of a more straightforward termination of pregnancy by suction evacuation rather than by dilatation and evacuation (“D&E”), which carries more risks for the mother and can be more psychologically distressing (for example, if the mother has felt fetal movements). In cases where the parents opt for the pregnancy to continue, the progression of the disease should be monitored as frequently as appropriate, usually about every 6–8 weeks. In some forms of CHD, the affected fetus will benefit from delivery in a tertiary care center, where perinatal management can be optimized.

The assessment of fetal growth with serial ultrasound scans is essential in women with severe heart disease and cyanotic congenital heart lesions. Uterine blood flow increases to 200 ml/min by the 28th week of gestation, and reaches approximately 1200 ml/min at term. Therefore, uterine blood flow and thus perfusion of the fetus is vulnerable if the cardiac output is in any way compromised. If the overall maternal cardiac output falls, then vascular resistance is altered, primarily to protect the mother and particularly to maintain cerebral and coronary artery blood flow. Uterine blood flow is therefore the first to suffer and is affected by changes in perfusion pressure and uterine vascular resistance. Hence, in women with cyanotic heart disease with reduced maternal cardiac output, uterine blood flow is further reduced, which leads to FGR. A retrospective cohort study of women with congenital and acquired heart disease showed a significant reduction in fetal growth rates, increased risk of preterm delivery, and a reduction in fetal birthweight. The presence of maternal cyanosis and a reduced cardiac output are the most significant predictors.[33]

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