Nearly 5% to 10% of pregnancies are complicated by high blood pressure. Hypertension-related deaths account for nearly 1/7th of the maternal deaths due to pregnancy. High blood pressure occurring in pregnancy is classified into various types depending on the onset and the other associated features. The table given below lists the major subtypes and summarizes the major differentiating features.
Table 1: Classification of High Blood Pressure during Pregnancy
Gestational Hypertension (Pregnancy-Induced Hypertension)
New onset hypertension in a woman who had normal blood pressure before 20 weeks’ gestation.
Preeclampsia and Eclampsia Syndrome
Preeclampsia –> Gestational Hypertension + Proteinuria.
Eclampsia –> Preeclampsia + Seizures
Preeclampsia Syndrome superimposed on Chronic Hypertension
Chronic hypertension that later develops features of preeclampsia.
Hypertension was also present before the start of pregnancy.
Of the conditions listed above, differentiating preeclampsia syndrome (alone or superimposed upon chronic hypertension) from other forms of high blood pressure is most important because it is the most dangerous form of raised blood pressure during pregnancy. The exact cause of hypertension or its aggravation during pregnancy is unknown. It is important to recognize the hypertensive disorders as early as possible because they can cause fetal-growth restrictions and increase the risk of complications during pregnancy.
In all the above conditions during pregnancy, the hypertension is differentiated into mild and severe.
It is important to note that the differentiation is not permanent for the remaining duration of the pregnancy. It only indicates the current status, and an apparently “mild” form may rapidly progress to severe form.
This is a new onset hypertension in a woman who had normal blood pressure before 20 weeks’ gestation. It is further classified into mild and severe, as mentioned above. Proteinuria (loss of protein in urine) is absent (if present, it is called preeclampsia). Nearly 50% of women with gestational hypertension will subsequently develop preeclampsia. The blood pressure returns to normal in less than 12 weeks after the delivery of the baby. Therefore, confirmation is made only after 12 weeks of delivery, if blood pressure remains elevated, it is termed chronic hypertension. If blood pressure returns to normal, and the preeclampsia syndrome did not develop during pregnancy, it is redesignated as transient hypertension.
The raised blood pressure during pregnancy (Systolic ≥ 140 mm Hg and/or diastolic ≥ 90 mm Hg) is termed chronic hypertension if hypertension antecedes pregnancy. Sometimes it may not be possible to know whether the women had hypertension before pregnancy, and the first recording of blood pressure is obtained after 20 weeks’ gestation. In such cases, it is not possible to differentiate between gestational and chronic hypertension until 12 weeks after the delivery. If hypertension persists after 12 weeks, then it is chronic hypertension. If blood pressure returns to normal within 12 weeks after delivery, then it was gestational hypertension.
If during pregnancy, the blood pressure of a woman with hypertension rises more than 30 mm Hg (Systolic) or more than 15 mm Hg (Diastolic), then it is termed as gestational hypertension superimposed on chronic hypertension. Similarly there can be preeclampsia superimposed on chronic hypertension if proteinuria develops in a hypertensive woman after 20 weeks’ gestation. Both, chronic hypertension and gestational hypertension predispose to development of preeclampsia and eclampsia.
Preeclampsia is the presence of proteinuria (daily loss of >300 mg of protein in urine) along with gestational hypertension. It is a “pregnancy-specific syndrome that can affect virtually every organ system.” Presence or absence of edema is no longer considered for diagnosing preeclampsia because it is very commonly present during pregnancy. Preeclampsia is also classified into mild and severe but criteria are slightly different for severe preeclampsia.
Mild Preeclampsia –> In addition to blood pressure criteria, the proteinuria should be less than 5 g per day.
Severe Preeclampsia –> In addition to blood pressure criteria, presence of any of the following will be termed severe preeclampsia (even if the blood pressure criteria are not met).
There are certain predisposing risk factors for preeclampsia. First pregnancy, maternal age greater than 35 years, family history, multiple fetuses (twins), diabetes, kidney diseases, hydatidiform mole and hydrops fetalis. Also, some women may develop atypical preeclampsia in which preeclampsia features may be present without hypertension and proteinuria.
Onset of seizures (convulsions) in a woman with preeclampsia is termed as eclampsia. The seizures should not be because of any other cause. The seizures are generalized and may develop before labor, during labor or even after labor.
The approach to management varies considerable depending upon the duration of gestation, fetal maturity, severity of the high blood pressure and maternal condition. For all conditions except chronic hypertension, the only definitive cure is delivery of the baby.
General approach is observation and bed rest for mild forms, and hospitalization and treatment with antihypertensive drugs for severe form. The antihypertensive drugs considered relatively safe in pregnancy are methyldopa, nifedipine, atenolol, hydralazine and labetalol. The first three are used for long-term management whereas the last two are used for short term control of blood pressure. If the period of gestation is >36 weeks and fetal lung maturity are present, then labor is induced. Also if there is a serious risk to mother or the fetus at any stage, induction of labor can be considered after evaluation of risks and benefits. Steroids are used to speed up fetal lung maturity if the period of gestation is less than 34 weeks. Fetal lung maturity is one of the most important things considered for induction of labor.
Preeclampsia, whether mild or severe, warrants hospitalization and careful observation. Severe preeclampsia needs control of blood pressure with antihypertensive drugs and anticonvulsive therapy with magnesium sulfate to prevent seizures.
Eclampsia is an obstetric emergency and requires prompt control of convulsions and blood pressure. Usually, delivery is done after the control of convulsions.