Normal fetal growth is a critical component of a healthy pregnancy and the long-term health of the offspring. Pivotal to understanding the dynamics of human fetal growth and to defining normal and abnormal fetal growth is the development of standards for fetal growth. The study's purpose was to establish standards for normal fetal growth and size for gestational age for 4 racial/ethnic groups of pregnant women with the eventual creation of individualized standards for fetal growth and improvements in fetal weight estimation. These data for a contemporary cohort of pregnant women should provide data for clinical management.

Summary and aims:

Normal fetal growth is a critical component of a healthy pregnancy and the long-term health of the offspring. Pivotal to understanding the dynamics of human fetal growth and to defining normal and abnormal fetal growth is the development of standards for fetal anthropometric parameters measured longitudinally throughout gestation, which, in turn, can be used to develop interval velocity curves and customized for genetic and physiological factors. We propose to conduct a multi-center prospective observational study (1) to establish a standard for normal fetal growth (velocity) and size for gestational age in the U.S. population; (2) to create an individualized standard for fetal growth potential; and (3) to improve accuracy of fetal weight estimation.

Eligibility:

• Healthy, low-risk pregnant women (both obese and nonobese) between the ages of 18 and 40 from each of the following four self-identified race/ethnicity backgrounds: African American, Asian, Caucasian, and Hispanic.

Design:

• Observational cohort design where pregnant women are recruited prior to 13 weeks gestation and followed throughout pregnancy and delivery for women having livebirths.
• After a sonogram at enrollment (10-13 weeks), women were randomized to receive sonograms according to one of the following four schedules: schedule A: 16, 24, 30, 34, and 38 weeks; schedule B: 18, 26, 31, 35, and 39 weeks; schedule C: 20, 28, 32, 36, and 40 weeks; schedule D: 22, 29, 33, 37, and 41 weeks.
• An enrollment interview was followed by depression screening, physical activity, anthropometric assessment and ultrasonology screening for measurement of fetal growth, and at each of the 5 subsequent visits.
• Uterine artery and fetal Doppler studies at selected gestational weeks.
• Women were asked to provide blood samples at enrollment and at follow-up visits at 16-22 weeks, 24-29 weeks, and 34-37 weeks of gestation.
• Neonatal anthropometry completed for all infants within 12-24 hours after birth.
• Cord blood, plasma, and placenta samples were collected for a smaller subsample of newborns.
• Post-study evaluations: Women who were diagnosed with gestational diabetes during pregnancy were asked to return for a follow-up visit 6 weeks after delivery.

Enrollment:

Final recruitment included 2,802 women with singleton pregnancies of which 2,334 were healthy, low-risk women with pre-pregnancy body mass indices (BMI) between 19-29.9 kg/m2. The racial/ethnic distribution of participating women were: Caucasians (n=614), African American (n=611), Hispanics (n=649), and Asians (n=460), and reflects natality characteristics of contemporary U.S. births. An additional 468 obese women (BMI 30-44.9 kg/m2) were also recruited.

Quality Control:

The quality of the ultrasound measures was guaranteed by implementation of: (1) a comprehensive quality control protocol for ante hoc training and credentialing of all site sonographers, developed by the sonology center at Columbia University, and (2) a rigorous protocol for post hoc quality control, whereby a random sample of all scans, stratified by clinical site and visit, was re-measured for accuracy and reliability.

• INCLUSION CRITERIA:
• Singleton, viable pregnancy
• 8 plus 0 - 13 plus 6 weeks of gestation
• Maternal age 18 - 40 years
• BMI 19.0 -29.9kg/m(2) for low risk group; BMI 30.0 - 45.0kg/m(2) for obese group
• Firm LMP
• LMP-date and ultrasound date match within 5 days for gestation estimates between 8 weeks + 0 days and 10 weeks + 6 days, 6 days for those between 11 weeks + 0 days and 12 weeks + 6 days, and 7 days for estimates between 13 weeks + 0 days and 13 weeks + 6 days
• No confirmed or suspected fetal congenital structural or chromosomal anomalies
• Expect to deliver at one of the participating hospitals
• No previous participation in the NICHD Fetal Growth Study

EXCLUSION CRITERIA:

• Smoked cigarettes or used illicit drugs in the six months
• Used illicit drugs in the past year
• Having at least 1 alcoholic drink per day
• Conception by ovulation stimulation drugs or assisted reproductive technology
• Chronic hypertension or renal disease under medical supervision
• Asthma requiring weekly medication
• Diabetes mellitus
• Thyroid disease under medical supervision
• Autoimmune disorder (rheumatoid arthritis, lupus, antiphospholipid antibody syndrome,scleroderma)
• Hematologic disorders (chronic anemia, sickle cell disease thrombocytopenia coagulation defects, thrombophilia)
• Cancer
• HIV or AIDS
• Epilepsy or seizure on medication or occurrence within 2 years
• Psychiatric disorder (bipolar disorder, depression, anxiety disorder currently requiring medication)
• Current anorexia nervosa or bulimia
• Previous severe preclampsia, eclampsia, HELLP syndrome
• Previous stillbirth or neonatal death
• Previous very preterm birth (less than 34 weeks)
• Previous low birthweight (less than 2,500 g)
• Previous macrosomia (greater than or equal to 4,500 g)

The following criteria apply only to obese women only:

• Chronic hypertension or high blood pressure requiring two or more medications
• Diabetes while not pregnant
• Chronic renal disease under medical supervision
• Autoimmune disease (rheumatoid arthritis, lupus, antiphospholipid antibody syndrome, scleroderma)
• Psychiatric disorder (bipolar disorder, depression, anxiety disorder currently requiring medication)
• Cancer (currently receiving treatment)
• HIV or AIDS

Women with singleton gestations (n=2,802) were enrolled from 12 U.S. clinical centers. Women were enrolled between 8w0d and 13w6d gestation, as measured by last menstrual period dating consistent with obstetrical ultrasonology.

Pregnancy and postpartum data will be made accessible in documented repositories and electronic archives after completion of the studies' analytical phases.

After completion of the studies' analytical phases.

The data, along with a set of guidelines for researchers applying for the data, will be posted to a data-sharing site. All requests for data must include a short protocol with a specific research question and a plan for analysis. Before receiving any analytical file, all users must complete a Data Use Agreement form.