Twins should be delivered short of full term but not too short, for the best chance at survival, said a study on Wednesday that analyzed over 35,000 births.
Current recommendations for twin births vary from 34 to 39 weeks, short of the normal 40 weeks of gestation, to lower the risk of still birth.
But premature delivery is associated with health complications for the children, making it a tough balance to strike.
For the new analysis, an international research team looked at 32 studies published in the past 10 years of women with uncomplicated twin pregnancies whose children died at birth or shortly thereafter.
They weighed data from 35,171 pregnancies to try to identify the optimal gestational age for twin delivery.
Of the pregnancies, 29,685 were dichorionic, meaning each twin had its own individual placenta, and 5,486 monochorionic, sharing a single placenta.
Scientists had previously observed a thirteenfold increase in stillbirths in monochorionic twins compared to single child pregnancies, and five-fold in dichorionic ones.
In duo-placenta pregnancies, the risk of stillbirth and neonatal death did not change until 37 weeks, the team found.
“However, delay in delivery by a week (to 38 weeks) led to an additional 8.8 deaths per 1,000 due to an increase in stillbirth,” said a statement on the study.