Twinning: A Marker for Biological Insults

Birth records of 314 consecutive twin births were analyzed with respect to race, sex, birth weight, gestational age, presentation and type of delivery, Apgar ratings, socioeconomic ratings, time lapsed between delivery of first and second twin, use of oxytocic drugs during labor, and frequency of diagnosis of multiple births. Twin neonates were found to be a nonrepresentative sample of newborns with respect to birth weight and gestation, with male pairs and same-sex pairs the least representative. Significant differences were found between Negro and Caucasian twins--Negroes having shorter gestation, lower birth weight and socioeconomic ratings but higher parity. One-third of the twins were delivered from breech presentation, and these infants had lower Apgar and socioeconomic ratings, shorter gestation, and lower birth weight. Twins recruited into a longitudinal study had more favorable perinatal conditions than the larger twin sample. Implications for clinicians as well as research scientists interested in intrapair differences in twins are discussed. The study of twins holds a unique place in efforts to define the genetic aspects of human development. The delineation of environmental factors is also crucial in this pursuit of genetic differences. The prenatal environment, conditions of birth, and related physiological status of the neonate are all potential sources of intrapair differences.