August 8, 2008 — In pregnant women, chronic hypertension, young or older maternal age, and recurrent early spontaneous abortions are associated with an increased risk for small-for-gestational-age (SGA) births, according to the results of a large, population-based, Danish study reported in the August issue of Obstetrics & Gynecology.

"Evidence relating chronic hypertension to risk of...SGA births is conflicting," write Janet M. Catov, PhD, from the University of Pittsburgh in Pennsylvania, and colleagues. "To identify factors associated with SGA that may involve a placental pathogenesis, we related chronic hypertension and other maternal factors that may be markers of endothelial dysfunction to preterm compared with term SGA births."

In the Danish National Birth Cohort (N = 81,008), chronic hypertension, diabetes, body mass index, age, and subfertility were related to the risk for term and preterm SGA births, defined as those with a birth weight adjusted for gestational age greater than 2 SDs below the mean on the basis of fetal growth curves.

In women with definite chronic hypertension, the risk for preterm SGA infants was 5.5-fold higher (95% confidence interval [CI], 3.2 - 9.4), and the risk for term SGA infants was 1.5-fold higher (95% CI, 1.0 - 2.2). Factors associated with a higher risk for preterm SGA but not for term SGA infants were maternal age younger than 20 years (odds ratio [OR], 2.8; 95% CI, 1.1 - 6.8) or maternal age older than 36 years (OR, 2.0; 95% CI, 1.3 - 3.1) and a history of 2 or more early spontaneous abortions (OR, 2.0; 95% CI, 1.3 - 3.3).

 

Other factors associated with a greater risk for term and preterm SGA infants were smoking, parity, time to pregnancy greater than 12 months, and underweight status, whereas overweight status, obesity, and maternal diabetes were unrelated to either subtype of SGA.

Limitations of this study include predominantly white study population, limiting generalizability to other ethnic groups; reliance on self-report for some study variables; and inability to distinguish cases of transient hypertension during pregnancy.

"Chronic hypertension, young or older maternal age, and recurrent early spontaneous abortions increased risk for preterm SGA," the study authors write. "These factors may involve abnormal placentation and likely represent a pathogenesis distinct from that leading to term SGA."

The National Heart, Lung and Blood Institute supported this study. The Danish National Research Foundation established the Danish Epidemiology Science Centre and supports the Danish National Birth Cohort, which is also supported by the Pharmacy Foundation, the Egmont Foundation, the March of Dimes Birth Defects Foundation, the Augustinus Foundation, and the Health Foundation. The study authors have disclosed no relevant financial relationships.

Obstet Gynecol. 2008;112:290-296.