A varying-coefficient logistic regression model The impact of twin pregnancy as a quadratic function of GA. Adjusted for confounders, e.g. prior still-birth, smoking. With & without adjustment for size at birth.
Is twin birth hazardous? Why? Twins had lower odds of death prior to 36 weeks of GA; higher odds thereafter. Longer GA was related to lower mortality. But the decline was sharper in singletons than in twins.
The role of fetal growth and size at birth? Without adjustment for size at birth the log OR climbed up faster after around 34 weeks. Twins’ mortality reached it’s lowest point at 38 weeks; it turned upward after that.
Clinical interpretations Twins have an earlier development In utero environment in late pregnancy not good for twins Residual confounding
Optimal GA for twins The optimal gestational age for twins appeared to be 37-39 weeks in terms of neonatal mortality. This is earlier than singletons’.
Readings 1Cheung YB, Yip P, Karlberg J. Mortality of twins and singletons by gestational age. Am J Epidemiol 2000;152:1107-16.Am J Epidemiol 2000;152 2Lie RT. Intersecting perinatal mortality curves by gestational age -- are appearances deceiving? Am J Epidemiol 2000;152:1117-19.Am J Epidemiol 2000;152 3Cheung YB, Yip P, Karlberg J. Respond to “Are appearances deceiving”. Am J Epidemiol 2000;152:1120.Am J Epidemiol 2000;152