16. Receipt of live vaccine during current pregnancy. 17. High risk for preterm birth (active preterm labor, short cervix, cervical cerclage, receipt of antenatal corticosteroids for fetal lung maturity prior to Visit 1) 18. Antenatal ultrasound diagnosis of fetal growth restriction, defined as < 10th percentile estimated fetal weight for gestational age 19. Known fetal congenital anomaly, e.g. genetic abnormality or malformation based on antenatal ultrasound 20. Any condition which, in the opinion of the investigators, may pose a health risk to the subject or interfere with the evaluation of the study objectives.