The Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) established the Nulliparous Pregnancy Outcomes Study: Monitoring Mothers-to-Be (nuMoM2b) to study women for whom the current pregnancy will lead to their first delivery (nulliparas). Nulliparas comprise about 40% of pregnant women in the United States. Because no information is available from previous pregnancy outcomes to guide assignment of risk or mitigating interventions, adverse pregnancy outcomes in nulliparas are especially unpredictable. The underlying mechanisms of adverse pregnancy outcomes such as preterm birth, preeclampsia, and fetal growth restriction are interrelated, and therefore will be evaluated as part of this study. The NuMoM2b study was a prospective observational study of over 10,000 nulliparous women followed from the first trimester through delivery to understand the mechanism and etiology of adverse pregnancy outcomes starting in the first trimester. It was conducted at eight clinical sites including Columbia University, Indiana University, Case Western and Ohio State Universities, University of California at Irvine , University of Pennsylvania, University of Pittsburgh, Northwestern University, and University of Utah. The data coordinating center was Research Triangle Institute (RTI) International and the Network. Enrollment of all I0,000 participants was completed in September of 2013 and the last participant delivered May 2014. All study participants underwent serial evaluations including demographics, nutrition, family history , maternal anthropometric measurements, medical history, assessments of psychosocial factors, ultrasound measures of fetal growth, placental function (uterine artery Doppler) and biospecimen collection (maternal serum, plasma, urine, cerv ical/vag in al samples, placenta at delivery).