Importance of the Multidisciplinary Team

A cardiologist with expertise in the diagnosis and management of congenital heart disease may have cared for a considerable number of women who have been through pregnancy, but they will not have the depth of knowledge to understand the full implications of cardiac compromise for the pregnant mother and her fetus. Equally, an obstetrician may have cared for many women with cardiac impairment, but that does not make him or her an expert on the diagnosis and management of heart disease. Only by consulting simultaneously with the same patient will these two professionals be able to meld their joint experience into appropriate advice and care for the woman with congenital heart disease. According to the circumstances, the team should also include an anesthetist, a specialist nurse, an intensivist, and a midwife or a neonatologist. Geneticists, ultrasonographers, radiologists, hematologists, and other specialists will need to be involved when appropriate. The multidisciplinary team (MDT) has a vital role in the provision of high-quality care, and it also provides the best insurance against inadvertent error or inappropriate advice, thus providing medicolegal protection. It also provides ongoing education and updating of the members.

Preconception Counseling

All women need appropriate information about contraception and pregnancy once this becomes a physiological possibility. It is particularly important in women with congenital heart disease that a proactive approach is adopted, with advice being given at the age of 12 to 15 years, depending on the maturity of the individual. This vital information should be given at the appropriate age and not delayed until she transfers to an adult cardiologic service. It should always be given in the context of the MDT and not delegated to an individual clinician, regardless of the clinician’s experience. The initial advice is likely to emphasize contraception, but the woman should be given at least an outline of the potential risks of pregnancy and the importance of seeking advice and obtaining an up-to-date evaluation of her cardiac status before conception is attempted. If she has a condition that is likely to deteriorate with age, it should be pointed out that, when this is an option, pregnancy at a younger age is preferable so that she can, if necessary, prioritize her desire for a family ahead of establishing a career. Information should include the mortality risk for the woman herself, and any increased risks to her baby. Although traditionally some conditions with a very high risk of mortality, such as pulmonary hypertension, were regarded as an absolute contraindication to pregnancy, there have always been some women prepared to take the risk, and recent reports suggest a steady reduction in mortality secondary to improvements in management. Nonetheless, women should be warned of the fact that not only might they die during pregnancy, but they may become ill or even die during their baby’s childhood, and therefore family support is particularly vital.

Risks for the baby include the likelihood of inheriting cardiac disease (this ranges from 3% to 5% in multifactorial conditions to as high as 50% in conditions with dominant autosomal inheritance such as Marfan syndrome). Knowledge of the genetics of heart defects is advancing at such a rate that it is no longer appropriate to quote a single figure for all cardiac abnormalities; instead, a literature search for the latest information on any particular condition is advisable. A useful resource is the Online Mendelian Inheritance in Man (OMIM) knowledgebase (available at http://www.omim.org/ ). If there is any doubt about the likely inheritance risk, the opinion of a clinical geneticist should be sought. In conditions where cardiac output is restricted or impaired, the incidence of fetal growth restriction is increased; in severe conditions, such as congenital cyanotic heart disease where oxygen saturation is low and hemoglobin consequently high (increasing blood viscosity and reducing placental blood flow), increased risk occurs in almost all cases. If maternal condition deteriorates during pregnancy and pregnancy has to be terminated, the baby faces all the risks of preterm birth.

Hemodynamic Changes in Pregnancy

The endocrine changes in pregnancy (notably a huge rise in the levels of progesterone, but also increases in other hormones such as estrogen and relaxin) have a major impact on the cardiovascular system. The most notable changes include a 30% to 50% increase in blood volume and a decrease in systemic vascular resistance of up to 80%. The latter is associated with a fall in systemic arterial blood pressure and an increase in heart rate. Cardiac output increases steadily during pregnancy until the 32nd week of gestation, and it reaches the plateau of up to 50% above the prepregnancy level. Subsequent changes in cardiac output are very dependent on maternal posture, with reductions seen in the supine position because of obstruction of venous return through the inferior vena cava as a result of pressure from the pregnant uterus. As a result, if there are any concerns about cardiac output, the mother should be placed in the left lateral position. The pain and stress of labor further increases cardiac output, although this can be minimized with the use of regional (epidural) anesthesia. Once the baby is delivered and the uterus retracts, the closure of the placental circulation results in a reduction of the intravascular volume of about 500 mL, which is usually balanced by a similar average blood loss. However, if blood loss is minimal, the extra circulating blood volume can overload the compromised heart, whereas a larger-than-average blood loss (resulting in a compensatory tachycardia) can also cause decompensation. Accordingly, the birth itself is a time of major risk, and the closest possible monitoring is required. The involvement of an experienced obstetric anesthetist is essential for the safe management of any woman with more than mild cardiac impairment. There are also major cardiovascular readjustments in the 24 to 48 hours following birth, notably a substantial diuresis as the blood volume returns toward normal. There is also an increase in coagulability of the blood; this is the time of major risk for deep vein thrombosis (DVT) and therefore pulmonary embolism (there is a sixfold increase in the incidence of DVT during pregnancy, and this rises to 11-fold in the puerperium). Most cardiovascular parameters return approximately to normal after 6 weeks, but full resolution of the changes can take up to 12 months.

The Prediction of Outcome

There have been many attempts to systematize the prediction of pregnancy outcomes. The earliest used the New York Heart Association (NYHA) classification devised in 1928:

However, more recently, additional scoring schemes have been devised to incorporate the results of modern investigative techniques, for example, the CARdiac disease in PREGnancy risk score, which was derived and validated in a prospective multicenter study of 599 pregnancies in women with a variety of congenital and acquired heart diseases. Further studies by Khairy et al. and Drenthen et al. (the ZAHARA score) provide additional risk calculators. In 2011, the task force on the management of cardiovascular diseases in pregnancy of the European Society of Cardiology advocated the use of a modified World Health Organization (WHO) classification of maternal cardiovascular risk. The reasoning behind this classification was that changes in the mother’s condition during pregnancy are often more closely related to the nature of the lesion itself than to the prepregnancy symptoms of the mother; cardiovascular performance is more tolerant of the physiologic changes in pregnancy in some conditions than in others. For example, valvular incompetence is better tolerated than stenosis. In the former, the degree of regurgitation is broadly proportional to the cardiac output and therefore percentage impairment changes relatively little during pregnancy. However, with stenosis, the degree of restriction increases geometrically with the cardiac output, and therefore percentage impairment increases substantially during pregnancy. A useful classification of the allocation of cardiac diagnosis into the various categories of risk was published in 2014 by Regitz-Zagrosek et al. Examples of conditions considered at high risk of maternal mortality (10% to 30%) include Eisenmenger syndrome, truncus arteriosus, pulmonary hypertension, and Marfan syndrome with an aortic root diameter of 4 cm or more. Moderate risk conditions (risk of mortality 1% to 10%) include mitral stenosis, aortic stenosis, systemic right ventricle, cyanotic lesions without pulmonary hypertension, and a Fontan-type circulation.

Principles of Antenatal Care

Women should be encouraged to contact their cardiologist as soon as they are confirmed pregnant, to arrange an early appointment with the MDT. Hopefully, they have followed the advice given at the preconception clinic and have had a recent thorough evaluation of their cardiac status. If not, this should be carried out as soon as possible. This enables the MDT to decide whether the patient’s care can be appropriately conducted at her local maternity unit, or whether she should be seen only at the tertiary center, or some combination of the two. A detailed plan of care should be established and should be fully documented in the woman’s notes (in the United Kingdom, it is national policy that all pregnant women carry an up-to-date copy of their maternity record). The plan of care should also be shared with all relevant professionals, including the family physician. The woman should be encouraged to carry her copy at all times so that it is immediately available to attending professionals in the event of an emergency. In addition to continuity of care, caregiver continuity is important because seeing the same person repeatedly enables the professional to detect subtle signs of deterioration compared with the previous consultation. Symptoms such as shortness of breath and palpitations should be enquired about at each visit, and exercise tolerance can be assessed by observing how quickly (or slowly) the woman walks to the consultation room. At each consultation there should be a careful clinical examination including (but not limited to) assessment of the pulse rate and rhythm (an increasing pulse rate or the occurrence of a new arrhythmia are important early signs of decompensation), and auscultation of the heart (to detect any change in murmurs) and lung bases (to detect early pulmonary edema). Although in relatively low-risk cases much of the care can be undertaken by the obstetrician alone (albeit at an increased frequency of consultations compared with normal pregnancy), all cases should be reviewed by the MDT several times during pregnancy (eg, delivery planning will commonly take place between 30 and 34 weeks), and weekly MDT reviews may be necessary in high-risk cases.

Fetal assessment usually begins at the 10-14 week ultrasound scan, which is done to check gestational age and for nuchal thickness measurement (part of Down/fetal anomaly screening). A raised nuchal thickness increases the likelihood of congenital heart disease and should lead to further detailed scans of the fetal heart. Diagnosis of some congenital cardiac conditions can be made as early as 14 weeks. All women with congenital heart disease should be offered a detailed fetal scan by a fetal cardiologist; this is most commonly done at 20 and 22 weeks when the heart is big enough to detect about 80% of significant cardiac anomalies, although in some centers this is a two-stage process, with an initial scan performed at 16 to 18 weeks. In women with impaired cardiac output or cyanosis, or where there is clinical suspicion of impaired fetal growth, fetal biometric scans should be carried out regularly—monthly if the initial scan is normal, but every 2 weeks if there is evidence of impaired growth. Weekly monitoring can be done by assessing flow velocity waveforms in the umbilical artery using Doppler techniques (in fetal growth restriction there is reduced and then absent diastolic flow), and daily monitoring if necessary can be done by cardiotocography (simultaneous continuous monitoring of the fetal heart rate and uterine contractions).

Principles of Care During Labor and Delivery

Labor and delivery are particularly high risk for the mother with heart disease because of the increased demands on the heart caused by the pain and physical exertion of labor and the very large hemodynamic changes that occur when the baby is born, the placenta is delivered, and the uterus retracts, closing off the uteroplacental blood flow, which had previously taken 25% of the cardiac output. It can be made even more stressful if there is a significant postpartum hemorrhage, more common for various reasons (including anticoagulation) in women with heart disease and occurring in up to 5% of births. At one time there was a perception that delivery by cesarean section was optimal because it avoided the stress of labor. However, this has been transformed by the widespread availability of regional anesthesia, which can achieve complete pain relief in 95% of women and partial pain relief in another 3%. Vaginal delivery is usually less disturbing to maternal physiology than cesarean section because it avoids major surgical trauma, and blood loss is on average only half that at cesarean. A 2015 study of 1262 deliveries concluded that in most cases the mother did not benefit from cesarean section and it resulted in earlier delivery of the baby with the accompanying disadvantages of immaturity. Accordingly, most cesarean sections in women with heart disease are now done for purely obstetric indications. In a few cases, cesarean section is performed because early delivery is necessary and the cervix is unripe, making induction of labor difficult, or because it is necessary to time delivery precisely for the purposes of regulating anticoagulation. Occasionally it may be necessary to perform an elective cesarean section to ensure attendance of key members of the obstetric cardiac team, or to conduct the delivery with detailed cardiac monitoring including transesophageal echocardiography.

Induction of labor is carried out for the usual obstetric indications (eg, fetal growth restriction, or pregnancy going more than 1 week past the due date) and is preferably carried out by rupturing the amniotic membranes and giving a carefully controlled intravenous oxytocin infusion. Prostaglandins can be used to ripen the cervix, but these carry a 3% to 10% risk of inducing uterine hyperstimulation (which can cause fetal hypoxia). Tocolytics such as ritodrine or salbutamol used to relax the uterus and counteract hyperstimulation are relatively contraindicated in women with cardiac disease because they cause tachycardia, and prostaglandins for induction of labor are therefore best avoided if possible.

Usual practice is to await the spontaneous onset of labor; however, it is important to emphasize to the patient that she is not going to have “natural childbirth.” Epidural anesthesia is recommended because it removes the stress of painful uterine contractions. A prolonged second stage of labor with repeated Valsalva maneuvers (bearing down or “pushing”) impairs venous return, which may be destabilizing, and so assisted delivery with forceps or a vacuum extractor is preferred after a length of time recommended by the MDT and established during delivery planning. The epidural should be placed by an experienced obstetrician and the local anesthetic (usually Marcaine) given by slow incremental top up to avoid sudden changes in blood pressure (hypotension). Any woman with a significant lesion should be monitored continuously during labor by ECG and oxygen saturation monitoring, and regular assessments of pulse rate and blood pressure (every 15 minutes). Best practice is to record observations on a specially designed chart. In cases of major heart disease, blood pressure is commonly monitored using an arterial line as this is more accurate in the event of significant hypotension. Continuous fetal heart rate and uterine activity monitoring (cardiotocography) is also recommended.