A short gestation age (GA) is defined as 28-34 weeks. As shown in the previous slide this range is more normal in twins than in singletons. Multiple logistic regression models were estimated in twins and singletons separately to examine the impact of nine factors on the risk of short GA (vs GA>34). Part of the findings are shown in the slide. Maternal smoking (vs non-smoking) and prior still-birth were more related to a short GA in singletons than in twins, supporting the claim that a shorter gestation was more pathological in singletons. The Hosmer-Lemeshow test suggested sufficient goodness-of-fit (each P>0.05).