To evaluate the representativeness of controls in an ongoing, population-based, case-control study of birth defects in 10 centers across the United States, researchers compared 1997-2003 birth certificate data linked to selected controls (n = 6,681) and control participants (n = 4,395) with those from their base populations (n = 2,468,697). Researchers analyzed differences in population characteristics (e.g., percentage of births at > or =2,500 g) for each group. Compared with their base populations, control participants did not differ in distributions of maternal or paternal age, previous livebirths, maternal smoking, or diabetes, but they did differ in other maternal (i.e., race/ethnicity, education, entry into prenatal care) and infant (i.e., birth weight, gestational age, and plurality) characteristics. Differences in distributions of maternal, but not infant, characteristics were associated with participation by selected controls. Absolute differences in infant characteristics for the base population versus control participants were < or =1.3 percentage points. Differences in infant characteristics were greater at centers that selected controls from hospitals compared with centers that selected controls from electronic birth certificates. These findings suggest that control participants in the National Birth Defects Prevention Study generally are representative of their base populations. Hospital-based control selection may slightly underascertain infants affected by certain adverse birth outcomes.

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Abstract-We used data from the National Birth Defects Prevention Study, a population-based, case-control study, to examine whether previously reported associations between antihypertensive medications and cardiovascular malformations could be confirmed and to explore whether new associations might be identified. Cases (nϭ5021) were ascertained through birth defects surveillance systems from 1997 through 2003 in 10 US states. Controls (nϭ4796) were live births without birth defects selected randomly from birth certificates or hospital discharge listings in the same geographic regions. Logistic regression was used to examine the relationship between antihypertensive medication treatment and the occurrence of cardiovascular malformations while controlling for confounding variables. First-trimester treatment with antihypertensive medication was associated with pulmonary valve stenosis (odds ratio [OR]: 2.6; 95% CI: 1.3 to 5.4), Ebstein malformation (crude OR: 11.4; exact 95% CI: 2.8 to 34.1), coarctation of the aorta (OR: 3.0; 95% CI: 1.3 to 6.6), and secundum atrial septal defects (OR: 2.4; 95% CI: 1.3 to 4.4). Treatment initiated after the first trimester was associated with pulmonary valve stenosis (OR: 2.4; 95% CI: 1.1 to 5.4), perimembranous ventricular septal defects (OR: 2.3; 95% CI: 1.2 to 4.6), and secundum atrial septal defects (OR: 2.4; 95% CI: 1.3 to 4.4). Untreated hypertension was associated with Ebstein malformation (OR: 2.1; 95% CI: 1.0 to 4.3) and secundum atrial septal defects (OR: 1.3; 95% CI: 1.0 to 1.6). Antihypertensive medication use and/or the underlying hypertension might increase the risk of having an infant with specific left and right obstructive and septal defects. Additional studies with adequate power will be needed to confirm these findings. Key Words: hypertension Ⅲ pregnancy Ⅲ antihypertensive agents Ⅲ congenital malformations Ⅲ cardiovascular malformations H ypertension occurs in 5% to 10% of pregnancies, 1-6 yet information on the safety of antihypertensive medication use during pregnancy is limited. For severe hypertension, antihypertensive medication is used to prevent serious maternal and fetal complications; however, there is no consensus on when to treat mild-to-moderate hypertension. Although treatment with medication might benefit the mother, it carries potential risks to the fetus from both impaired uteroplacental perfusion and fetal exposure to the medications. Angiotensinconverting enzyme (ACE) inhibitors and angiotensin II receptor blockers, 2 classes with similar mechanisms of action, are contraindicated during the second and third trimesters because of a well-known fetopathy. 1-11 The ␤-blocker atenolol has been associated with intrauterine growth retardation. [1][2][3][4][5][6][12][13][14] One concern is that hypertension or iatrogenic hypotension might cause cardiovascular malformations (CVMs) by altering perfusion in the placenta and/or fetus. [15][16][17][18][19] In rats, abnormal cardiac development has resulted from exposures to calcium channel blockers, angiote...