Further defining the risks confronting twins.

We report the absolute and relative risks for neonatal and infant death, low and very low birth weight, and delivery at < 33 and < 35 weeks' gestation in twin pregnancy stratified by maternal race and age, as well as gender pair combinations of the twins. Data on 324,141 twin infants were obtained from the 1985 to 1988 U.S. Linked Birth/ Infant, Death Data Sets. In this observational cohort study, we analyzed the outcomes of 138,779 twin pregnancies of white and black women that ended with the delivery of two live-born infants. Rates for the aforementioned outcomes are increased for black infants, for male-male pairs compared with male-female pairs (with female-female pairs being intermediate), and for young mothers. For male-male twins born to young (< or = 22 years old) black women, relative risks range from 2.1 for both pair members being low birth weight (< 2500 gm) to 5.0 for both pair members dying in infancy, when male-female pairs born to older (> or = 28 years) white women served as the reference group. Although all twin pregnancies are at higher risk than singletons, risk is influenced by maternal race and age, as well as gender pair combination. These analyses provide useful information for counseling women pregnant with twins. Furthermore, they suggest that failure to consider variations in baseline risk may have seriously flawed studies evaluating prophylactic interventions in twin pregnancy.