Preterm birth occurs in approximately 18 percent of live births to black mothers and is reported to be increasing in incidence. Black infants have a risk of mortality two times higher than white infants. Much of this difference is attributed to the higher rate of preterm delivery, but little is understood about the factors that can result in preterm birth. Samadi and Mayberry conducted a case-control study to assess the effects of chronic hypertension preceding pregnancy and pregnancy-induced hypertension on preterm delivery in black mothers.
National hospital discharge records between 1988 and 1993 were used to identify black mothers with spontaneous preterm births. Among the 2,347 study patients who had preterm deliveries and the 23,857 control subjects who had full-term deliveries, 547 (2.1 percent) were identified as having chronic hypertension before pregnancy, and 1,144 women (4.4 percent) met criteria for pregnancy-induced hypertension.
The risk of preterm delivery was almost doubled in women with either chronic (odds ratio: 1.8) or pregnancy-induced (odds ratio: 1.6) hypertension. The risk was particularly high in mothers with pregnancy-aggravated hypertension. After adjusting for confounding factors, these mothers were found to have four times the risk of preterm delivery as nor-motensive mothers. Other significant conditions such as poor fetal growth, antepartum hemorrhage and placental separation were more prevalent in mothers of preterm infants than in control subjects. The increased risk of preterm birth in hypertensive women was significant after adjustment for these factors plus age, marital status and insurance type.
The authors stress the contribution of hypertensive conditions to preterm birth. Because chronic hypertension is 2.5 times more common in black women than in white women, significantly more black women enter pregnancy at risk of premature birth. Black women with pregnancy-aggravated hypertension are at particularly high risk of premature delivery. Consequently, infants born to these women are at increased risk of morbidity and mortality. Although much more information regarding the relationship between maternal hypertension and preterm birth remains to be elucidated, monitoring and controlling risk factors for preterm delivery in black patients with hypertension has the potential to reduce infant mortality and morbidity.