Maternal race/ethnicity and twinning rates in the United States, 1989-1991

OBJECTIVE: To utilize United States birth certificate data (years 1989-1991 ) to examine the effects of race/ethnicity on twinning rates. STUDY DESIGN: We used a database of birth certificate data for the United S tates (years 1989-1991) available on CD-ROM from the United States National Center for Health Statistics. This linked birth/infant death data set incl uded a total of 12,036,234 birth records, of which 279,073 were twins. Excl uded from the analysis were 15,086 twin birth records (5.4%) based upon pre viously described exclusion criteria. Statistical analysis included a serie s of univariate analyses to determine the rates of twinning between differe nt racial/ethnic groups correlated with maternal age, education, marital st atus and place of birth. Comparisons were analyzed using the chi (2) test, with significance at P <.05. RESULTS: The overall twinning rate was 2.26%, with the lowest rate observed in the group denoted non-Hispanic other (1.67%) and highest among non-Hisp anic blacks (2.69%). Twinning rates within various groups representing Hisp anics ranged from 1.76% to 2.08%. The twinning rate was significantly highe r among U.S.-born as compared to non-U.S.-born women (2.34% vs. 2.88%, P<.0 05) except far Puerto Ricans, Cubans and Central/South Americans ,for whom the reverse was true, Women aged 35-39 had the highest twinning rate (3.05% ), whereas women aged 15-19 had the lowest; that trend persisted in all rac ial/ethnic groups. The study showed a nonsignificant relationship between m arital status or education and twinning rate. CONCLUSION: Race/ethnicity studies can be useful in designing programs that may maximize health outcomes of twins in a racially diverse population.