High blood pressure is quite common in pregnant women, and can cause harm to both the baby and the mother. It occurs in one percent of all pregnant women. Early diagnosis and treatment, however, can usually prevent harm.
Blood pressure normally falls during pregnancy due to a general relaxing of the mother’s blood vessels. It reaches a low point about halfway through the pregnancy and then slowly rises so that at the mother’s due date her blood pressure has reached its non-pregnant level.
Three conditions may produce high blood pressure during pregnancy
- Chronic High Blood Pressure
- Gestational Hypertension
Chronic High Blood Pressure
Chronic high blood pressure is high blood pressure starting before pregnancy. Almost all of the women with this condition have Essential Hypertension which means that these women have high blood pressure due to unexplained reason. This blood pressure may shoot up during the first trimester of pregnancy and then come down to normal during the second trimester (normal means the woman’s original blood pressure before she became pregnant). This blood pressure may again shoot up in the last few months or during labour. This may sometimes pose a threat to the expectant mother or the foetus.
A second condition, called Pre-eclampsia, arises only during pregnancy and disappears after the foetus is delivered. Preeclampsia is defined as the appearance of high blood pressure, ankle swelling and protein in the urine during the second half of pregnancy. It usually occurs in the first pregnancy and mostly does not occur in subsequent ones. It runs in families and occurs more often in mothers with chronic high blood pressure, chronic kidney disease, diabetes, multiple foetuses and in mothers at the extremes of child-bearing age (i.e., teenagers or those above 35 years of age).
Pre-eclampsia may cause headache, blurred vision and ultimately seizures in the mother. There is often a decrease in the urine production or a build up in the blood of dietary waste products, normally eliminated by the kidneys. Abdominal pain and abnormal blood clotting may occur. In addition, the growth of the foetus in the womb may be retarded.
The third condition causing high blood pressure during pregnancy is called gestational hypertension. It is defined as high blood pressure without swelling or protein loss in the urine, occurring in a mother who had normal blood pressure before conception. It usually arises in the late stages of pregnancy and resolves within two weeks after delivery. It usually occurs in later pregnancies.
The term “Toxemia” is often used loosely to refer to any type of hypertension in pregnancy (usually pre-eclampsia).
Management of Blood Pressure in Pregnant Women
Regular blood pressure checks are especially important during pregnancy. If high blood pressure is discovered during pregnancy the doctor first determines whether pre-eclampsia is present, and if it is present, to what severity. Women with pre-eclampsia are usually admitted to hospital for observation because this condition can change from mild to severe over 24 to 48 hours. Women with mild pre-eclampsia can be managed with bed rest and drugs that lower elevated pressures.
Women with severe pre-eclampsia (severe blood pressure elevation and multiple organs involved) require treatment of their blood pressure with intravenous medication and urgent delivery of the baby, as they will not improve until the pregnancy is ended. Fortunately pre-eclampsia does not cause the development of high blood pressure later in life.
Women with gestational high blood pressure are managed in the same manner as those with chronic high blood pressure. But women with gestational high blood pressure have more chances of developing high blood pressure later in life.
Patients with chronic high blood pressure that becomes worse during pregnancy can be managed as out-patients. Those who are working/ employed are asked to stay home and those at home are asked to take bed rest. Drugs that lower the blood pressure are advised in consultation with the gynaecologist/obstetrician.
Blood pressure in pregnant women has to be monitored continuously as little elevation can also cause certain damage to the mother and foetus.
Uncontrolled high blood pressure during pregnancy requires treatment. Blood pressure-lowering treatment for all types of high blood pressure in pregnancy provides benefit to the mother and possibly the foetus. Most doctors begin medication that lowers elevated pressures when the mother’s diastolic blood pressure is 100 mm Hg or greater. The goal is usually to achieve a diastolic pressure of 80 to 90 mm Hg because a lower blood pressures may be dangerous for the foetus as they may reduce blood flow to the uterus.
At least five different blood pressure lowering drugs have been found for use in pregnancy, and are considered to be effective without endangering the development of the foetus. These are methyldopa, atenolol, and labetolol. Other acceptable drugs, although less extensively studied in pregnancy, are clonidine, prazosin and nifedipine.
Therapy is usually begun with one drug. A second and then a third drug are added if necessary. If the blood pressure cannot be controlled with three drugs, it is unlikely to come down with the addition of more medication, and delivery should be undertaken for the mother’s safety.
Two types of drugs are usually avoided during pregnancy. Diuretics may increase the risk of low birth weight for infants. Angiotensin-converting enzyme inhibitors, such as captopril and enalapril, may cause growth retardation. Other agents including monoxide and calcium antagonists (such as diltiazen and verapamil), are not yet considered suitable for use in human pregnancy because their safety during pregnancy has not been shown.