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Clubfoot, a common major structural malformation, develops early in gestation. Epidemiologic studies have identified higher risks among boys, first-born children, and babies with a family history of clubfoot, but studies of risks associated with maternal exposures are lacking. We conducted the first large-scale, population-based, case-control study of clubfoot with detailed information on maternal medication use in pregnancy. Study subjects were ascertained from birth defect registries in Massachusetts, New York, and North Carolina during 2007-2011. Cases were 646 mothers of children with clubfoot without other major structural malformations (i.e., isolated clubfoot); controls were mothers of 2,037 children born without major malformations. Mothers were interviewed within 12 months of delivery about medication use, including product, timing, and frequency. Odds ratios were estimated for exposure to 27 medications in pregnancy months 2-4 after adjustment for study site, infant sex, first-born status, body mass index (weight (kg)/height (m)(2)), and smoking. Odds ratios were less than 1.20 for 14 of the medications; of the remainder, most odds ratios were only slightly elevated (range, 1.21-1.66), with wide confidence intervals. The use of antiviral drugs was more common in clubfoot cases than in controls (odds ratio = 4.22, 95% confidence interval: 1.52, 11.73). Most of these results are new findings and require confirmation in other studies.

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.

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 ator =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 wereor =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.

The preterm delivery rate in North Carolina is consistently higher than the national average. However, recent reports suggest that singleton preterm delivery rates for non-Hispanic Whites are increasing while those for non-Hispanic African Americans are decreasing. To study this pattern further, the authors examined data on singleton non-Hispanic White and non-Hispanic African-American births in 1989 and 1999 by using North Carolina vital statistics data. They found that the frequency of preterm delivery rose 1.1% (8.5% to 9.6%) among non-Hispanic Whites but declined 1.4% (17.9% to 16.5%) among non-Hispanic African Americans over the same time period. For both subgroups, a bimodal distribution of birth weights was apparent among preterm births at 28-31 weeks of gestation. The second peak with its cluster of normal-weight infants was more prominent among non-Hispanic African Americans in 1989 than in 1999. To reduce the potential for bias due to misclassification of infant gestational age, frequencies of preterm delivery of infants who weighed less than 2,500 g were calculated. Unlike the original analysis, this calculation showed that preterm delivery increased for both subgroups. A number of non-Hispanic African-American births classified as preterm were apparently term births mistakenly assigned short gestational ages. Such misclassification was more frequent in 1989 than in 1999, inflating 1989 preterm delivery rates.