Association between stillbirth and risk factors known at pregnancy confirmation.

CONTEXT

Stillbirths account for almost half of US deaths from 20 weeks' gestation to 1 year of life. Most large studies of risk factors for stillbirth use vital statistics with limited data.

OBJECTIVE

To determine the relation between stillbirths and risk factors that could be ascertained at the start of pregnancy, particularly the contribution of these factors to racial disparities.

DESIGN, SETTING, AND PARTICIPANTS: Multisite population-based case-control study conducted between March 2006 and September 2008. Fifty-nine US tertiary care and community hospitals, with access to at least 90% of deliveries within 5 catchment areas defined by state and county lines, enrolled residents with deliveries of 1 or more stillborn fetuses and a representative sample of deliveries of only live-born infants, oversampled for those at less than 32 weeks' gestation and those of African descent.

MAIN OUTCOME MEASURE

Stillbirth.

RESULTS

Analysis included 614 case and 1816 control deliveries. In multivariate analyses, the following factors were independently associated with stillbirth: non-Hispanic black race/ethnicity (23.1% stillbirths, 11.2% live births) (vs non-Hispanic whites; adjusted odds ratio [AOR], 2.12 [95% CI, 1.41-3.20]); previous stillbirth (6.7% stillbirths, 1.4% live births); nulliparity with (10.5% stillbirths, 5.2% live births) and without (34.0% stillbirths, 29.7% live births) previous losses at fewer than 20 weeks' gestation (vs multiparity without stillbirth or previous losses; AOR, 5.91 [95% CI, 3.18-11.00]; AOR, 3.13 [95% CI, 2.06-4.75]; and AOR, 1.98 [95% CI, 1.51-2.60], respectively); diabetes (5.6% stillbirths, 1.6% live births) (vs no diabetes; AOR, 2.50 [95% CI, 1.39-4.48]); maternal age 40 years or older (4.5% stillbirths, 2.1% live births) (vs age 20-34 years; AOR, 2.41 [95% CI, 1.24-4.70]); maternal AB blood type (4.9% stillbirths, 3.0% live births) (vs type O; AOR, 1.96 [95% CI, 1.16-3.30]); history of drug addiction (4.5% stillbirths, 2.1% live births) (vs never use; AOR, 2.08 [95% CI, 1.12-3.88]); smoking during the 3 months prior to pregnancy (<10 cigarettes/d, 10.0% stillbirths, 6.5% live births) (vs none; AOR, 1.55 [95% CI, 1.02-2.35]); obesity/overweight (15.5% stillbirths, 12.4% live births) (vs normal weight; AOR, 1.72 [95% CI, 1.22-2.43]); not living with a partner (25.4% stillbirths, 15.3% live births) (vs married; AOR, 1.62 [95% CI, 1.15-2.27]); and plurality (6.4% stillbirths, 1.9% live births) (vs singleton; AOR, 4.59 [95% CI, 2.63-8.00]). The generalized R(2) was 0.19, explaining little of the variance.

CONCLUSION

Multiple risk factors that would have been known at the time of pregnancy confirmation were associated with stillbirth but accounted for only a small amount of the variance in this outcome.