The effect of pregnancy on the heart
What effect does pregnancy have on the healthy cardiovascular system?
The cardiovascular system starts to adapt to a pregnancy in the 6th week of gestation. These changes are regulated by a complex set of hormonal factors. The volume of blood in the pregnant woman’s body increases steadily over the following weeks, reaching a peak between the 30th week of gestation and the date of giving birth. At this stage of pregnancy, the volume of blood circulating in the woman’s body is 50% higher than before she became pregnant. This means that the cardiovascular system is being called upon to transport a significantly greater volume of blood at all times. The woman’s blood pressure, heart rate and respiratory rate gradually increase to deal with this constant additional workload.
A further significant increase in blood pressure, heart rate and cardiac output takes place at the onset of contractions, when around half a litre of blood is released into the peripheral blood vessels. During and after delivery, a large quantity of blood is diverted to the vascular system as a consequence of uterine contractions and the compression of the inferior blood veins leading to the heart (vena cava). In the weeks following childbirth, all of these vital functions gradually return to normal. It takes about 4 weeks for normal circulatory functions to be restored. In other words, pregnancy and childbirth call for a well-functioning cardiovascular system.
The gradual changes undergone by the human body in the process of bearing a child could be compared to the extreme physical effort demanded of a competitive athlete. The only difference between the two cases is that a pregnant woman has no possibility to take a breather when the going gets hard. But is should be remembered that pregnancy is not an illness; it is a condition that the body is designed to adapt to and to cope with.
Trying to conceive a child
What constraints should a woman with a congenital heart defect bear in mind before attempting to become pregnant?
Every young woman with a congenital heart defect ought to know her own body and be aware of the limits of her heart functions. Before deciding to attempt a pregnancy, she should consult her cardiology specialist to discuss the specific factors related to her congenital heart defect. She should undergo extensive cardiovascular tests, including spiroergometry examinations, and in more severe cases undergo a CAT scan and/or a cardiac catheterisation.
These tests will enable the patient’s general practitioner to offer competent advice, drawing attention to the risks involved and recommending the appropriate decision. In most cases, it will be possible to draw up a program of medical surveillance to be followed throughout the pregnancy and during childbirth, in consultation with an obstetrician. In rare cases, it might be recommended that the patient should undergo a surgical operation or intervention to ameliorate her cardiovascular health before attempting to fall pregnant.
Each type of heart defect has its own specific patho-morphological and functional characteristics. The factors that determine whether pregnancy is advisable or not depend not only on the type of heart defect but also on the “repairs” that have been conducted by catheterization or surgery. The degree of impairment of cardiovascular functions depends on the individual progress of the disease, and can vary from normal to light to severe. For this reason, it is imperative that a woman should ask the cardiologist treating her case to assess her personal vascular functions and stress resistance before falling pregnant. This is the only way to determine the risks faced by the future mother and her unborn child during the course of pregnancy and childbirth.
The following conditions present a serious risk to patients with congenital heart defects during pregnancy:
- Myocardial insufficiency (weakness of the heart muscle),
- Cardiac dysrythmias,
- Syncope (sudden loss of consciousness),
- Endocarditis (inflammation of the heart valve),
- Development of thromboses and embolisms,
- Brain abscesses,
- Increased risk of cyanosis,
- Tearing of the main artery,
- Tearing of already dilated parts of the main cardiac or cerebral arteries, or
- Sudden cardiac death.
Typical dangers for the unborn child are:
- premature birth,
- abnormally low birth weight.
Risks classified by seriousness of heart defect
Certain patients run the unfortunate risk that their cardiovascular condition might be seriously aggravated by pregnancy and childbirth, and could involve a high risk of mortality for the mother and/or her baby. In such cases, the considered medical advice is to avoid pregnancy altogether. Even if such news is “difficult to swallow”, most women agree to follow their doctor’s advice once they have understood the implications. After all, who would be willing to jump out of an aircraft without a parachute?
The following table provides an overview of selected heart defects and the associated risks in the event of pregnancy. This by no mean implies that a certain type of heart defect automatically presents no danger – it is always necessary to seek personal medical advice, otherwise the consequences could be fatal. For instance, a woman who has a relatively simple heart defect such as an occluded atrial septum, but whose heart muscles have been weakened by this condition, runs a high risk of developing a life-threatening cardiac insufficiency during pregnancy and childbirth. On the other hand, an increasing number of women with severe heart defects can nowadays be given the necessary treatment to allow them to bear children, whereas several years ago this option was considered too dangerous.
What methods exist to avoid a life-threatening pregnancy?
A reliable form of contraception is absolutely essential. This matter must be discussed with the patient’s gynaecologist. Hormonal contraceptives (“the pill”) are well tolerated by many women, but it must be borne in mind that there is a significant risk of thrombosis. The contraceptive coil is a very reliable means of avoiding pregnancy, but presents a risk of endocardiitis. Preventive treatment with antibiotics is essential when the coil is inserted. The safest solution of all is sterilisation. In view of the risks associated with a general anaesthetic, which are particularly elevated in the case of patients with a severe heart defect, such interventions should only take place in a specialised gynaecological clinic equipped to deal with high-risk patients, in close consultation with a centre for congenital heart defects.
Author: Dr. med. Ulrike Bauer
Last updated 12 May 2005