Pregnancy, and particularly childbirth, place great stress on the heart and circulatory system in many ways. As the placenta (the organ that develops in the uterus that provides oxygen & nutrients, and takes away waste from the foetus) develops, the total volume of the circulatory system increases. It is estimated that a healthy person bearing a 3.3kg foetus will have a blood plasma volume approximately 1300ml (50%) greater than prior to pregnancy.¹
This rapid expansion of the circulatory system, and other effects pregnancy hormones have on the blood vessels, usually leads to a fall in blood pressure during the first 24 weeks of pregnancy. Having said this, blood pressure usually remains within the normal range, and doesn’t represent a problem unless it falls below about 90/60 mmHg (normal blood pressure is 120/80 mmHg) (source: NIH National Heart Lung and Blood Institute).
Other effects of increased blood volume are that the heart beats faster, and harder, to handle the extra blood, increasing cardiac output to properly supply the placenta and foetus with oxygen and nutrients.
Conditions That Can Develop During Pregnancy
There are three main conditions affecting the heart and blood vessel (cardiovascular) system which are of concern in pregnancy, and they are often interconnected.
Peripartum cardiomyopathy, also called postpartum cardiomyopathy, is a rare form of heart failure, which occurs in the peripartum (near birth) period (the last month of pregnancy to five months postnatally) and involves damage to the muscle of the heart, weakening it. The reason this happens is not currently known.
- Shortness of breath.
- Swollen ankles.
- Swollen neck veins.
- Chest pain.
- The sensation of missed heartbeats (asystole).
- Heart palpitations.
Peripartum cardiomyopathy tends to occur most often in those with the following characteristics:
- Multiple previous pregnancies
- Aged 30+
- Carrying more than one foetus
- Have preeclampsia (see below)
- Personal history of heart conditions like myocarditis.
Other risk factors include coronary artery disease, viral heart infection, some inherited diseases, excess alcohol consumption and smoking. Treatments for this condition aim to avoid excess fluid accumulation in the lungs (pulmonary oedema). They include ACE inhibitors, beta blockers and diuretics.
Those who have had this condition are discouraged from becoming pregnant again as the condition can often recur, particularly if their heart function has not returned to the pre-pregnancy baseline. If recovered, pregnancy can be attempted again provided regular echocardiograms and cardiac stress tests are done to monitor heart function.
Preeclampsia is a pregnancy-induced rise in blood pressur,e accompanied by protein in the urine, that affects about 6% of pregnant people - usually in the second half of pregnancy - and resolves after birth. It is usually mild but a severe form, called eclampsia, can be life-threatening. Preeclampsia is believed to begin in the placenta.
In those with preeclampsia, the new blood vessels that develop to efficiently supply the placenta with blood do not form or function properly, limiting the amount of blood that can flow through them. Causes of this abnormality may include insufficient blood flow to the womb, damage to the blood vessels, an immune system problem or a genetic predisposition.
Preeclampsia is one of four blood pressure disorders that can occur during pregnancy, the others are:
- Gestational hypertension.
- Chronic hypertension.
- Chronic hypertension with superimposed preeclampsia.
Risk factors for preeclampsia include:
- Personal or family history of preeclampsia.
- Chronic hypertension.
- First pregnancy.
- First pregnancy with a new partner.
- Age greater than 35.
- Black/Afro-Caribbean ancestry.
- Multiple pregnancy, e.g. twins.
- Having babies less than two years or more than 10 years apart.
- History of certain conditions before you become pregnant, such as chronic high blood pressure, migraines, type 1 or type 2 diabetes, kidney disease, or lupus.
- In vitro fertilisation.
The more severe the preeclampsia and the earlier in pregnancy it occurs, the higher the risk to mother and baby. Complications of preeclampsia may include:
- Foetal growth restriction. If the placenta doesn't get enough blood, this can lead to foetal growth restriction, low birth weight or preterm birth.
- Preterm birth. If preeclampsia is severe, the delivery may need to be induced early to save the life of both mother and baby.
- Placental abruption. The placenta can separate from the inner wall of the uterus before birth, which can cause heavy bleeding.
- HELLP syndrome. HELLP (Haemolysis, Elevated Liver enzymes and Low Platelet count) syndrome is a more severe form of preeclampsia, causing nausea, vomiting, headache and upper right abdominal pain.
- Eclampsia. When preeclampsia isn't well controlled eclampsia, essentially preeclampsia plus seizures, can develop.
- Other organ damage; damage to the kidneys, liver, lung, heart, or eyes, and possibly a stroke or other brain injury.
- Cardiovascular disease. Having preeclampsia may increase your risk of future cardiovascular disease.
Gestational diabetes is relatively common after week 28 of pregnancy, affecting up to 18% of those that carry a baby to term. Like other forms of diabetes, it can cause a dry mouth, the need to urinate frequently, infections such as thrush, and fatigue.
There are also effects on the baby; gestational diabetes increases the risk of larger than normal birth weight, increasing the likelihood of needing a caesarean section. It can also cause polyhydramnios, which is an excess of amniotic fluid in the womb, leading possibly to premature labour or birth difficulties. Gestational diabetes may also be one of the causes of preeclampsia, and can cause foetal jaundice (yellow skin and eyes).
It is usually managed with diet and lifestyle factors such as exercise, but severe cases might require medication such as metformin or insulin.If it is caught early and well-managed it doesn’t cause severe problems, but if not, it can cause premature birth and health issues for the baby such as low blood sugar.
Although this condition resolves after birth (usually), having gestational diabetes increases the mother’s risk of having it the next time she is pregnant and also increases the risk of developing type 2 diabetes. Risk factors for gestational diabetes include:
- Body mass index (BMI) is above 30; use this BMI calculator to work out your BMI.
- Previously bearing a baby weighing 4.5kg (10lb) or more at birth.
- Having gestational diabetes in a previous pregnancy.
- One or more parents or siblings with diabetes.
- Being of South Asian, Black, African-Caribbean or Middle Eastern ethnicity.
Should You Get Pregnant if You Have a Heart Condition?
Existing heart problems can be exacerbated by the stresses of pregnancy. If you have any heart condition, you should seek specialist medical advice before trying to conceive. For those with some heart conditions, pregnancy is inadvisable and termination may be recommended, according to MSD Manuals and the British Heart Foundation.
These conditions include:
- Severe pulmonary artery hypertension.
- Certain heart birth defects include coarctation of the aorta.
- Marfan syndrome.
- Loeys–Dietz syndrome.
- Severe aortic valve stenosis.
- Severe mitral valve stenosis.
- An aortic valve with two instead of three flaps.
- Cardiomyopathy from a previous pregnancy.
- Moderate or severe heart failure.
Cardiovascular disease is the leading cause of death in pregnancy. According to the Preventive Cardiovascular Nurses Association (PCNA), more than 33% of pregnancy-related deaths are due to some type of cardiovascular cause, including heart attack, cardiomyopathy and stroke.
Preventing Heart Problems
Heart problems such as structural defects of heart valves cannot be prevented, but coronary artery diseases respond well to a range of preventative measures. These include eating healthily, getting regular exercise, cutting out smoking, and moderating alcohol intake. A healthy diet would include plenty of fruit and vegetables, wholegrains, lean proteins and a minimum of saturated fat, salt and sugar, such as that found in highly processed foods.
Preeclampsia prevention may be partly possible if you begin taking a daily aspirin by about 12 weeks gestation, on the advice of your doctor. According to the Cleveland Clinic, taking a baby aspirin each day can decrease the risk of developing preeclampsia by approximately 15%.
Eating healthily, getting plenty of sleep, taking regular exercise and controlling your blood pressure and blood sugar (if you have high blood pressure or diabetes prior to pregnancy) can all mitigate the risk of heart problems.
Gestational diabetes may be prevented by losing weight before conception if you are overweight and taking regular exercise. You should not try to lose weight if you are already pregnant, as gradual moderate weight gain is important for the health of the baby. A healthy diet and regular exercise are important whether you have diabetes or not.
Pregnancy massively increases the stress experienced by your cardiovascular system. Those with a range of pre-existing heart conditions are strongly advised to avoid becoming pregnant. In addition, pregnancy can give rise to conditions that affect the heart and circulatory system. These are peripartum cardiomyopathy, preeclampsia and gestational diabetes, and each has a range of adverse effects on mother and baby.