Trends in twin birth outcomes and prenatal care utilization in the United States, 1981-1997

Context Multiple births account for an increasing percentage of all low-birth-weight infants, preterm births, and infant mortality in the United States. Since 1981, the percentage of women with multiple births who received intensive prenatal care (defined as a high number of visits, exceeding the recommendation of the American College of Obstetricians and Gynecologists by approximately 1 SD beyond the mean number of visits for women initiating care within each trimester) has increased significantly. Objectives To explore the hypothesis that more aggressive management of twin-birth pregnancies may be associated with changes in birth outcomes in this population. Design, Setting, and Subjects Cross-sectional and trend analysis of data from the National Center for Health Statistics' birth and infant death records for all twin births occurring in the United States between 1981 and 1997, excluding those with missing or inconsistent data. Main Outcome Measures Trends in preterm birth, low birth weight, preterm and term small-for-gestational-age (SGA) births, and infant mortality, by level of prenatal care utilization. Results The preterm birth rate for twins increased from 40.9% in 1981 to 55.0% in 1997, The percentage of low-birth-weight infants increased from 51.0% to 54.0%, The preterm SGA rate also increased from 11.9% to 14.1%, while the term SGA rate decreased from 30.7% to 20.5%. For women with intensive prenatal care utilization, the preterm birth rate increased from 35.1% to 55.8%, compared with an increase from 50.6% to 592% among women with only adequate use. Twin preterm deliveries involving either induction or first cesarean delivery also increased from 21.9% to 27.3% between 1989-1991 and 1995-1997. The twin infant mortality rate for women with intensive prenatal care use declined between 1983 and 1996 and remained lower than the overall twin infant mortality rate. Conclusions An apparent increase in medical interventions in the management of twins may result in the seeming incongruity of more prenatal care and more preterm births; however, these data suggest that women with intensive prenatal care utilization also have a lower infant mortality rate.