Log odds of neonatal mortality as estimated by a logistic regression model with varying coefficients for twin pregnancy. NOT adjusted for size at birth. Adjusted for sex, maternal smoking, maternal age, mother's health, parity, prior stillbirth, prior neonatal death, congenital abnormality, and year of birth.

Without adjustment for size at birth, the mortality curve for twins turned upward after reaching it's lowest point at 38 weeks.