Blood pressure during pregnancy in a Swedish population; impact of parity

Hypertension represents the most commonly encountered complication of pregnancy. Normal levels of blood pressure (BP) need to be established in each pregnant population in order to recognize pathology. A lack of studies from our own country and certain methodological objections to early studies motivated this study.

Six hundred pregnant women were included in a historical cohort. The maternal BP had been measured with a mercury sphygmomanometer and standardized routines at each antenatal visit. Data regarding age, baseline BMI, weight gain and smoking habits as well as parity had been recorded.

BP values were overall somewhat higher than in international studies, the SBP increasing slightly towards term. The diastolic blood pressure (DBP) decreased slightly until 25-28 weeks of gestation. A steady increase thereafter led to values at term 7.3% above initial values. In nulliparae the increase was significantly greater, 9.9% versus 5.4% in multiparae. Primigravidae showed mean DBP levels significantly higher than all multigravidae towards term. The DBP was correlated with the baseline BMI, but not with age or weight gain. In smoking pregnant women the DBP showed a significantly greater initial decrease and failed to follow the subsequent rise to the same degree as in non-smokers.

Slightly higher blood pressure levels were found in this study compared to other international studies. Multiple regression analysis showed that parity, baseline BMI and smoking all significantly influenced the DBP at term. Multiparae have significantly lower DBP levels in pregnancy compared to nulliparae. The first pregnancy seems to have the greatest impact in lowering the blood pressure in subsequent pregnancies.