Inclusion Criteria:

• Maternal age ≥ 18 years and ability to give informed consent.
• Singleton gestation
• Ultrasound examination that confirms or revises the EDD before 14 weeks of gestational age
• Gestational age ≥ 35 weeks' gestation
• Normal aneuploidy screening (1st trimester screening, 2nd trimester screening, integrated screening, NIPT) when performed
• Spontaneously conceived pregnancy (i.e the current pregnancy is not the result of in vitro fertilization)

Exclusion Criteria:

• Fetal chromosomal or genetic abnormalities if invasive prenatal diagnosis is performed
• Fetal malformations or soft markers identified on fetal anatomy survey
• Episodes of uterine bleeding after 24 weeks gestation. Unobserved self-reported bleeding with confirmed intact pregnancy on ultrasound after the bleeding episode is not an exclusion criteria.
• Uterine/placental abnormalities including uterine malformations (i.e bicornuate uterus, didelpus uterus), abnormal placentation (placenta previa, accreta, percreta), uterine fibroids.
• Cerclage in the current pregnancy
• History of intrauterine fetal demise
• History of fetal growth restriction or birth weight > 4Kg in a previous pregnancy
• Fetal isoimmunization or alloimmunization
• Fetal demise in previous pregnancies
• Cancer (including melanoma but excluding other skin cancers). Dysplastic or pre-neoplatic conditions such as cervical intraepithelial neoplasia are admissible.
• Endocrine disease including thyroid disease (recently diagnosed or whose medication dose is not stable), adrenal disease, diabetes mellitus (pregestational and gestational).
• Renal disease with altered renal function (creatinine > 0.9, proteinuria > 300 mg/24 hour)
• Epilepsy or other seizure disorder
• Any collagen disease (lupus erythematosus, scleroderma, etc.)
• Active liver disease (acute hepatitis, chronic active hepatitis, persistently abnormal liver enzymes). Liver disorders accounting for cholestasis (including cholestasis of pregnancy) if diagnosed prior to enrollment.
• Hematological disorder including alloimmune and isoimmune thrombocytopenia but excluding mild iron deficiency anemia (Hb > 9 gm/dl). Patients with sickle cell disease are excluded.
• Chronic pulmonary disease including asthma requiring regular use of medication and active TB. An asthma inhaler used on an as needed basis for a cold or an asthma attack is not considered regular use.
• Heart disease except mitral value prolapse not requiring medication
• Cardiovascular disorders: chronic hypertension, gestational hypertension or preeclampsia diagnosed prior to enrollment
• Infectious diseases: HIV, CMV, toxoplasmosis, parvovirus B19, HBV, HCV
• Chronic treatments with medications such as aspirin, steroids, anti-hypertensive agents, immunosuppressants, antineoplastic drugs.
• Prior laparoscopic or open uterine surgeries where the uterine cavity was entered (such as myomectomies)
• Resectoscopic myomectomies (prior resectoscopic polypectomies are not contraindications)
• Prior classical cesarean deliveries.