A Relative Rise in Blood Pressure From 18 to 30 Weeks' Gestation Is Associated With Reduced Fetal Growth and Lower Gestational Age at Delivery: Much Ado About Nothing?
H ypertensive disorders in pregnancy include gestational hypertension, chronic hypertension, and preeclampsia. Collectively, these disorders complicate 6% to 20% of all pregnancies. 1 The rates of hypertensive disorders of pregnancy (HDP) will continue to increase because of the trend regarding advanced maternal age and increased body mass index at time of pregnancy. 1 These disorders, particularly preeclampsia, are more commonly associated with increased rates of small for gestational age
... infants, preterm birth (PTB), and lowbirth-weight infants. PTB is defined as delivery at <37 weeks' gestation, and it can be spontaneous because of either preterm labor or preterm rupture of membranes (spontaneous PTB) or indicated PTB as a result of maternal or fetal reasons. 2 SGA is defined as birth weight at <10th percentile, and low birth weight is defined as a birth weight of <2500 g. There is some evidence that preeclampsia and pregnancies complicated by SGA have similar risk factors, suggesting that they may share similar pathophysiology. For example, women with prior history of preeclampsia are at increased risk for SGA and preeclampsia in subsequent pregnancies, and women who are born SGA are at increased risk of preeclampsia and SGA in subsequent pregnancies. 3 In addition, women with prior history of preeclampsia are at increased risk for PTB and SGA even when they have subsequent normotensive gestation. 4 However, the cause of SGA and PTB is multifactorial, and only SGA and PTB related to placental insufficiency probably share abnormal placentation as a common pathway with preeclampsia. Indeed, most cases of SGA and PTB are not related to placental insufficiency. 2, 5 Two recent prospective studies evaluated the association between blood pressure (BP) values early in gestation and subsequent changes during pregnancy and development of HDP and SGA infants. 6,7 Bakker et al 6 evaluated changes in BP values that were measured in 6493 women in their the first trimester (mean weeks of gestation=13.2), in 8046 in their second trimester (mean weeks of gestation=20.4), and in 8119 in their third trimester (mean weeks of gestation=30.2). Macdonald-Wallis et al 7 also studied BP changes at 8 to 18, 18 to 30, 30 to 36, and >36 weeks' gestation in 13 016 women enrolled in the Avon Longitudinal Study of Parents and Children. The findings of these 2 studies suggest that an increase in BP from the second to the third trimester was associated with increased risk of HDP, SGA, and low-birth-weight infants. 6,7 In addition, Zhang et al 8 examined whether systolic and diastolic BP levels at baseline (12-19 weeks) and a rise in these BP values in third trimester (30-34 weeks) in 5167 healthy, normotensive, nulliparous women were associated with spontaneous PTB. They found that a rise in systolic BP >30 mm Hg or a rise in diastolic pressure >15 mm Hg was associated with a 2-to 3-fold increase in the risk of spontaneous PTB. In this issue of Hypertension, Macdonald-Wallis et al 9 describe novel data indicating that patterns of BP change during gestation are associated with fetal growth, birth weight, and gestational age at delivery. The study included repeat antenatal BP measurements (median of 10 measurements per woman) in 9697 women enrolled in the Avon Longitudinal Study. Bivariate linear spline models were used to relate changes in systolic and diastolic BP values at different gestational age periods (8-18, 18-30, 30-36, and >36 weeks' gestation) to subsequent perinatal outcome. On follow-up, 4.6% of pregnancies resulted in preterm delivery, 20% were complicated by HDP, and 80% remained normotensive. The authors found that in pregnant women who had normotensive pregnancies, both systolic and diastolic BP decreased from a baseline at 8 weeks to a nadir value at 18 weeks' gestation. In addition, they found that a steeper increase in systolic and diastolic BP between 18 and 36 weeks' gestation was associated with subsequent lower offspring birth weight and with an infant being born smaller for gestational age. They also noted that the associations of late BP change with fetal growth and length of gestation were independent of the level of BP early in pregnancy. Moreover, a smaller decrease in systolic and diastolic BP value before 18 weeks' gestation and a greater increase from 18 to 36 weeks were also associated with a shorter duration of gestation. They concluded that the associations observed between a steeper increase in BP that did not reach hypertensive levels and reduced fetal growth could represent an underlying placental pathology.