Delayed prenatal care and the risk of low birth weight delivery.

To determine if the timing of prenatal care is associated with low birth weight delivery after adjusting for sociodemographic and behavioral risk factors, we performed a retrospective cross-sectional study of singleton births to white (2,945,595) or African-American (552,068) women in the United States in 1996. When adjusted for race, maternal age, educational level attained, and the use of alcohol and tobacco during pregnancy, women beginning care in the 2nd (adjusted RR = 0.85; 95% CI: 0.83-0.86) and 3rd trimesters (RR = 0.87; 95% CI: 0.84-0.91) had a reduced risk of low birth weight compared to women beginning care in the 1st trimester. Our findings suggest that no benefit exists for early initiation of prenatal care for reducing the risk of low birth weight. Findings related to differences in low birth weight among women who start prenatal care later are likely due to sociodemographic differences that may influence access to early care.