Birth weight discordance, intrauterine growth retardation and perinatal outcomes in twins.

In a population-based study, the association between twin perinatal outcome, birth weight discordance and intrauterine growth retardation (IUGR) was investigated. Mortality was examined in 1,145 twin pairs, and neonatal morbidity was studied in 315 live-born pairs. In this study, birth weight discordance was defined as > or = 25% of the weight of the heavier twin, and IUGR was defined as < 10th percentile of gender- and gestational age-specific singleton birth weight. In univariate analyses IUGR and discordance were associated with mortality but not with morbidity. When twins were categorized by discordance and IUGR simultaneously, stillbirths were associated with IUGR, while discordant twins had elevated risks of early neonatal death. In multiple logistic regression analyses, which also included gestational age, mode of delivery, birth order, birth weight discordance and IUGR, low birth weight was the single consistent factor associated with elevated risks of mortality and morbidity. For every 250-g increase in birth weight, the risks for each condition examined fell by about 40%. Discordance was an independent risk factor only for hypoglycemia, while IUGR was not associated with any neonatal outcome. Birth weight itself seems to be the most important factor associated with perinatal outcome in twin births. Therefore, the weight of the individual fetus should be the focus of concern of the medical profession in the effort to reduce adverse outcomes in twin pregnancies.