Recurrence of stillbirth in sibships: Population-based cohort study.

Knowledge of stillbirth recurrence risk is of clinical interest and may give etiological insight. The authors studied "gestational age-" and "weight-by-gestation-specific" stillbirth recurrence, and evaluated time trends in a population-based cohort study from the Medical Birth Registry of Norway, from 1967 to 2004. Singleton births, including stillbirths from 20 weeks' gestation, were linked to their mothers by national identification numbers. Stillbirth rates in second pregnancies among mothers with (N = 5,091) and without (N = 562,057; the reference group) a stillbirth in first pregnancies were compared across 4 gestational age and 3 weight-by-gestation groups. A remarkable symmetric pattern of gestational age-specific recurrence of stillbirth was found, with highest odds of stillbirth in the same age group. The adjusted odds ratio values associated with preterm stillbirth recurrence were high, for example, 25.7 (95% confidence interval: 19.8, 33.3) for stillbirth at 20-27 weeks' gestation (73/1,511 vs. 1,021/562,057), while lower for term stillbirth: adjusted odds ratio = 2.3 (95% confidence interval: 1.2, 4.7) (9/1,844 vs. 1,021/538,499). The proportion of second early stillbirths in the population attributable to previous early stillbirth was 6.4%, compared with 0.5% for second term stillbirth. Over time, recurrence of early stillbirth decreased, whereas that of mid/late stillbirth did not change significantly. A symmetric pattern of recurring stillbirth in similar weight-by-gestation groups was not found.