Stillbirth in twins, exploring the optimal gestational age for delivery: a retrospective cohort study.

OBJECTIVE

To evaluate the optimal gestational age at delivery for twins.

DESIGN

Retrospective cohort study.

SETTING

Database containing demographic, delivery, and pregnancy outcome data for over 600,000 births from 81 hospitals in Alberta, Canada.

POPULATION

All twin births in Alberta, Canada, during 1992-2007, as recorded in the databases of the Alberta Perinatal Health Project (www.aphp.ca).

METHODS

The case files were reviewed for cause of death and any information regarding the gestational age at diagnosis of stillbirth. Multivariate logistic regression was used to examine the impact of potentially confounding factors. The 'fetus at risk' approach was used to evaluate the prospective risk of stillbirth. Competing risks of stillbirth and neonatal death were evaluated with a perinatal risk ratio.

RESULTS

Of a total of 17,724 twin births there were 236 antepartum stillbirths, 26 intrapartum stillbirths, and 244 neonatal deaths. The rate of stillbirth peaked at 7.0/1000 fetuses at risk at 38 weeks of gestation. On multivariate analysis, small for gestational age (odds ratio, OR 2.2; 95% confidence interval, 95% CI 1.35-3.59), birthweight discrepancy >20% (OR 2.67, 95% CI 1.42-5.03), and an interaction between these two variables (OR 2.94, 95% CI 1.31-6.59), were significant. The perinatal risk ratio suggested that the risks of delivery and expectant management were balanced at 36 weeks of gestation (RR 0.6, 95% CI 0.1-5.4), but the confidence interval included one, the null value, until 38 weeks of gestation (RR 0.1, 95% CI 0.02-0.40). The majority of stillbirths at term (14/25) occurred in monochorionic diamniotic twins. The estimated risk of stillbirth in this group was 2.3/1000 fetuses at risk at 37 weeks of gestation, and 17.4/1000 fetuses at risk at 38 weeks of gestation.

CONCLUSIONS

The balance of risk between neonatal death/intrapartum stillbirth and antepartum stillbirth begins to favour delivery at 36 weeks of gestation, particularly in monochorionic diamniotic twins.