 Nulliparous women with an in utero singleton gestation between 6 weeks 0 days and 13 weeks 6 days of pregnancy were recruited through the eight clinical sites and their subsites. Mechanisms were created in the various prenatal clinics associated with the sites to identify eligible nulliparous women with singleton pregnancies. Once enrolled, a participant was followed for the duration of her pregnancy by research staff at the clinical site. Study visits were scheduled at four times during the pregnancy: 6 weeks 0 days through 13 weeks 6 days estimated gestational age EGA, 16 weeks 0 days through 21 weeks 6 days EGA, 22 weeks 0 days through 29 weeks 6 days EGA, and at the time of delivery. Data were collected through personal interview, self-administered questionnaires, clinical measurement, chart abstraction, and collection of biological specimens blood, urine, cervico-vaginal fluid. Additional data i.e., sleep breathing assessments, actigraphy, fetal adrenal gland measurements were collected through ancillary research studies on subsets of the enrolled women. The set-ups for screening, enrollment and follow-up of participants varied by clinical site and subsite. However, in each setting, the clinical site staffs included study investigators, research nurses, research assistants and sonographers. Clinical site staffs were trained to interview participants, collect and process samples, conduct various research tests, and input data. Data are managed at the DCAC. Specimens are stored at the NICHD specimen repository for later analysis. 