The National Birth Center Study. Part I--Methodology and prenatal care and referrals.

This is the first of three articles that will report on the complete findings from the National Birth Center Study (NBCS). This article describes the study methodology, compares the entire group of NBCS subjects with all women who gave birth in the United States in 1986, describes the prenatal care and prenatal referral practices of birth centers in the study, and describes the women who were admitted to the birth centers for intrapartum care with regard to characteristics known or thought to be associated with perinatal risk. Nearly 18,000 women were included in the study; two-thirds of them (n = 11,814) were admitted to the birth centers for intrapartum care. Although medical and obstetric complications were the most common reason for discontinuing birth center care, they accounted for less than half of the women who were not admitted to the birth centers for labor and delivery; many women left for a variety of other reasons. In addition to describing birth center clients, birth center care providers, and birth center care, the NBCS provides detailed information about the characteristics and experiences during pregnancy of a large population of essentially low-risk women receiving a low-intervention style of maternity care.