NICHD Fetal Growth Studies

Eunice Kennedy Shriver National Institute Of Child Health & Human Development

Investigators

Linked publications, trials & patents

Abstract

The primary goal of this study was to establish a standard for normal fetal growth (velocity) and size for gestational age in the U.S. population. Additional goals were to create an individualized standard for fetal growth potential and to improve accuracy of fetal weight estimation. In the primary study from the NICHD Fetal Growth Studies Singletons, we created intrauterine fetal growth charts for size and velocity. (Buck Louis et al. American Journal of Obstetrics and Gynecology 2015; Grantz et al. American Journal of Obstetrics and Gynecology, 2018). Our team followed up this original work and created a unified, multi-ethnic fetal growth and fetal growth velocity standards, weighted using 2011 U.S. births. (Grantz KL et al. American Journal of Obstetrics and Gynecology, 2021 and Grantz KL et al. American Journal of Obstetrics and Gynecology, 2022) From these novel data, Dr. Grantz has led work to develop five publicly available online calculators: Fetal Growth Calculators Home | NICHD - Eunice Kennedy Shriver National Institute of Child Health and Human Development including an EFW percentile calculator and an EFW fetal growth velocity calculator. In collaboration with outside investigators, we investigated the complexity of how fetal growth restriction is identified in clinical practice. The Society for Maternal-Fetal Medicine's (SMFM) diagnostic criteria for fetal growth restriction (FGR) recently added abdominal circumference (AC) <10th percentile to estimated fetal weight (EFW) <10th percentile; however, its prediction of neonatal morbidity was unknown. We found that adding AC <10th percentile to the EFW <10th percentile definition of FGR significantly increased the incidence of FGR but did not improve the prediction of neonatal morbidity in a low-risk population. These findings indicate that the SMFM guideline for FGR should be adopted with caution. Ongoing work is evaluating definitions in a high-risk population. (Shea et al. Journal of Ultrasound and Medicine, 2025) Current work also aims at improving accuracy in birthweight prediction by sonographic estimated fetal weight (EFW). Accurate estimation of fetal weight informs clinical decision making in obstetrics; predicting birthweight from EFW has clinical implications encountered daily. Incorrect estimation of fetal weight may alter recommendations for cesarean birth. In fetuses which are small, incorrect estimation of fetal growth restriction can lead to unnecessary fetal testing, alter delivery timing, and if undetected, be associated with increased perinatal morbidity and mortality. Unfortunately, conventional formulas to calculate EFW have substantial error with only 80-87% accuracy in predicting birthweight within ± 15%. We compared differences in head circumference (HC), abdominal circumference (AC), femur length, and EFW between ultrasound and corresponding birth measurements within 14 (n = 1,290) and 7 (n = 617) days of birth for small- (SGA, <10th percentile), appropriate- (AGA, 10th-90th), and large-for-gestational age (LGA, >90th) newborns. Differences between fetal and neonatal HC were larger at 14 versus 7 days, and similar to patterns for EFW and birthweight, differences were the largest for LGA at both intervals. In contrast, differences between fetal and neonatal AC were larger at 7 versus 14 days, suggesting larger error in AC estimation closer to birth. Our findings suggest that differences in ultrasound versus birth measurements are influenced by ultimate neonatal size for gestational age as well as ultrasound timing. (Gleason et al. American Journal of Perinatology 2024) Work is ongoing to further improve prediction of birthweight. Cohort with Obesity Obesity is common among women of reproductive age and is known to increase the risk for maternal and fetal pregnancy complications. The NICHD Fetal Growth Studies enrolled 468 obese women with singleton pregnancies with the goal of comparing fetal growth patterns between women with obesity and non-obese women. Furthermore, because pregnancy complications such as GDM and preeclampsia are more common in women with obesity, this additional cohort offers the opportunity to examine how fetal growth is impacted by such complications. The researchers found that as early as 32 weeks' gestation, fetuses of obese women had higher weights than fetuses of nonobese women (Zhang et al. JAMA Pediatrics 2018). Our team evaluated the diagnostic accuracy of sonographic estimated fetal weight (EFW) in predicting small (SGA) or large (LGA) for gestational age birthweight and examined whether the accuracy was associated with maternal body mass index (BMI). EFW had acceptable accuracy for predicting LGA, unaffected by BMI. However, for SGA, EFW accuracy was significantly higher in the overweight/obese group, suggesting BMI influences diagnostic performance in SGA but not LGA classification. (Ghosal et al. Diagnostics, 2025 In press). Dichorionic Twin Cohort Twin gestations represented 3.4% of U.S. births in 2013, yet there was limited contemporary data on the estimation of fetal growth trajectories in twins. The NICHD Fetal Growth Studies enrolled 171 dichorionic twin pregnancies. The primary objective was to empirically define the trajectory of fetal growth in dichorionic twins using longitudinal two-dimensional ultrasonography and to compare the fetal growth trajectories for dichorionic twins with those based on a growth standard developed by our group for singletons. (Grantz et al. American Journal of Obstetrics and Gynecology, 2016) Compared with singleton fetuses, the mean abdominal circumference and estimated fetal weight trajectories of dichorionic twin fetuses diverged significantly beginning at 32 weeks. Her team also identified a significant gap in knowledge regarding child growth in twins. In the first study to compare longitudinal trajectories from birth through 18 y, comparing twins and singletons from the same underlying population, twins were smaller in height, weight, and BMI through age 18. (Gleason et al. The Lancet Child and Adolescent Health, 2025 In press) Differences persisted when conducting various adjustments for gestational age (GA) at delivery suggesting that smaller twin size is independent from earlier average GA at delivery for twins relative to singletons. In addition, unlike growth-restricted singletons, twins had no increased risk of being overweight and obesity—risk for twins was lower throughout childhood and early adolescence, with no difference in risk in late adolescence.