Blood pressure adjustments throughout healthy and hypertensive pregnancy: A systematic review and meta-analysis

Gestational hypertensive complications are preceded by deviant hemodynamic adjustments affecting blood pressure. Our objective was to determine the timing and magnitude of changes in blood pressure during singleton normotensive and hypertensive pregnancies. PubMed (NCBI) and Embase (Ovid) databases were searched for relevant studies up to November 2019. Studies reporting original blood pressure measurements during pregnancy together with a non-pregnant reference measurement were included. Studies including women with a history of cardiovascular or metabolic disease, or women using antihypertensive drugs were excluded. Pooled mean differences between pregnant and non-pregnant women, and absolute blood pressure values were calculated for predefined gestational intervals in normotensive and hypertensive pregnancy, using a random-effects model. Meta-regression analysis was used to analyze group differences in adjustments. In early normotensive pregnancy, both systolic and diastolic blood pressure decreased, reaching their maximum reduction of -4 mmHg (95%CI -6 to -1 mmHg) and -4 mmHg (95%CI, -5 to -3 mmHg), respectively in the second trimester. Thereafter, blood pressure gradually increased towards non-pregnant values. All absolute blood pressure measurements throughout normotensive pregnancy were below 130/80 mmHg. In hypertensive pregnancies, only diastolic blood pressure decreased early in pregnancy. In conclusion, this meta-analysis showed a clinically moderate, but significant mid-pregnancy drop in blood pressure during normotensive pregnancy. Reference curves with absolute values underscore the current liberal cut-off limit for gestational hypertension. A lack of a mid-pregnancy systolic blood pressure drop might reflect increased vascular resistance in women destined to develop hypertensive pregnancy complications.