Hypertension in Pregnancy

Early in the first trimester there is a fall in blood pressure caused by active vasodilatation, achieved through the action of local mediators such as prostacyclin and nitric oxide. This reduction in blood pressure primarily affects the diastolic pressure and a drop of 10 mm Hg is usual by 13-20 weeks gestation. Blood pressure continues to fall until 22-24 weeks when a nadir is reached. After this, there is a gradual increase in blood pressure until term when pre-pregnancy levels are attained. Immediately after delivery blood pressure usually falls, then increases. Even women whose blood pressure was normal throughout pregnancy may experience transient hypertension in the early post partum period, perhaps reflecting a degree of vasomotor instability.

Hypertension in pregnancy is diagnosed either from an absolute rise in blood pressure or from a relative rise above measurements obtained at booking. The conven-

• Mercury sphygmomanometers are preferable to automated blood pressure monitors
• If automated devices are used they should be calibrated, and checked regularly, against a mercury sphygmomanometer
• Use an appropriate sized cuff
• Woman should be seated or lying at 45° angle, with arm at level of the heart
• Record blood pressure to the nearest 2 mm Hg
• Use phase V Korotkoff sound (sound disappearance) to measure diastolic blood pressure

ANTENATAL CARE General Maternal Care

When to treat hypertension during pregnancy

Significant hypertension must be treated in its own right, regardless of the assumed underlying pathology, largely to reduce the risk of maternal intracranial hemorrhage.

The level at which antihypertensive treatment is initiated for nonsevere hypertension remains controversial, depending on whether treatment is focused on maternal or fetal wellbeing. Most physicians commence antihypertensive medication when the systolic blood pressure > 140-170 mm Hg or diastolic pressure > 90-110 mm Hg. Treatment is mandatory for severe hypertension when the blood pressure is 170/110 mm Hg. Once treatment is started, target blood pressure is also controversial, but many practitioners would treat to keep the mean arterial pressure < 125 mm Hg—for example, a blood pressure of 150/100 mm Hg. Overzealous blood pressure control may lead to placental hypoperfusion, as placental blood flow is not autoregulated, and this will compromise the fetus. Unfortunately there is no evidence that pharmacological treatment of chronic or gestational hypertension protects against the development of preeclampsia. Changes in diet or bed rest have not been shown to provide maternal or fetal benefit.

All antihypertensive drugs have either been shown, or are assumed, to cross the placenta and reach the fetal circulation. However, as previously stated, none of the C antihypertensive agents in routine use have been documented to be teratogenic, although ACE inhibitors and ARBs are fetotoxic. The objective of treating hyper-tension in pregnancy is to protect the woman from C/9 dangerously high blood pressure and to permit continuation of the pregnancy, fetal growth and maturation.