Trend analysis of the sex ratio at birth in the United States.

OBJECTIVES This report presents total sex ratios at birth from 1940 to 2002, for race starting in 1970, for Hispanic origin groups starting in 1989, for live birth order starting in 1943, and for age of mother for the full time period. METHODS Descriptive tabulations of sex ratios using the birth data set are presented and interpreted. Joinpoint regression analysis is used to detect changes in the sex ratio over time. RESULTS The United States sex ratio at birth had three significant transitions from 1940 to 2002 (1942, 1959, and 1971). White women were the only race group to have any significant changes in the sex ratio between 1970 and 2002 (1972, 1976, and 1988). Between 1940 and 2002 significant transitions in sex ratios occurred to women aged 20-24 (1942, 1966, 1974, and 1987); 25-29 (1961 and 1968); 35-39 (1965 and 1976); and 40-44 years (1967).