Original Research
Obstetrics
Fetal growth velocity standards from the Fetal Growth Longitudinal Study of the INTERGROWTH-21st Project

https://doi.org/10.1016/j.ajog.2020.07.054Get rights and content
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Background

Human growth is susceptible to damage from insults, particularly during periods of rapid growth. Identifying those periods and the normative limits that are compatible with adequate growth and development are the first key steps toward preventing impaired growth.

Objective

This study aimed to construct international fetal growth velocity increment and conditional velocity standards from 14 to 40 weeks’ gestation based on the same cohort that contributed to the INTERGROWTH-21st Fetal Growth Standards.

Study Design

This study was a prospective, longitudinal study of 4321 low-risk pregnancies from 8 geographically diverse populations in the INTERGROWTH-21st Project with rigorous standardization of all study procedures, equipment, and measurements that were performed by trained ultrasonographers. Gestational age was accurately determined clinically and confirmed by ultrasound measurement of crown-rump length at <14 weeks’ gestation. Thereafter, the ultrasonographers, who were masked to the values, measured the fetal head circumference, biparietal diameter, occipitofrontal diameter, abdominal circumference, and femur length in triplicate every 5 weeks (within 1 week either side) using identical ultrasound equipment at each site (4–7 scans per pregnancy). Velocity increments across a range of intervals between measures were modeled using fractional polynomial regression.

Results

Peak velocity was observed at a similar gestational age: 16 and 17 weeks’ gestation for head circumference (12.2 mm/wk), and 16 weeks’ gestation for abdominal circumference (11.8 mm/wk) and femur length (3.2 mm/wk). However, velocity growth slowed down rapidly for head circumference, biparietal diameter, occipitofrontal diameter, and femur length, with an almost linear reduction toward term that was more marked for femur length. Conversely, abdominal circumference velocity remained relatively steady throughout pregnancy. The change in velocity with gestational age was more evident for head circumference, biparietal diameter, occipitofrontal diameter, and femur length than for abdominal circumference when the change was expressed as a percentage of fetal size at 40 weeks’ gestation. We have also shown how to obtain accurate conditional fetal velocity based on our previous methodological work.

Conclusion

The fetal skeleton and abdomen have different velocity growth patterns during intrauterine life. Accordingly, we have produced international Fetal Growth Velocity Increment Standards to complement the INTERGROWTH-21st Fetal Growth Standards so as to monitor fetal well-being comprehensively worldwide. Fetal growth velocity curves may be valuable if one wants to study the pathophysiology of fetal growth. We provide an application that can be used easily in clinical practice to evaluate changes in fetal size as conditional velocity for a more refined assessment of fetal growth than is possible at present (https://lxiao5.shinyapps.io/fetal_growth/). The application is freely available with the other INTERGROWTH-21st tools at https://intergrowth21.tghn.org/standards-tools/.

Key words

correlation models
fetal growth
fetal growth velocity
fetal velocity standards
longitudinal study

Cited by (0)

The authors report no conflict of interest.

A.T.P. is supported by the Oxford Partnership Comprehensive Biomedical Research Centre, with funding from the National Institute for Health Research Biomedical Research Centre funding scheme. This project was supported by a generous grant from the Bill & Melinda Gates Foundation (grant no. 49038) to the University of Oxford. The funder played no role in the study design, analysis, or paper preparation.

Cite this article as: Ohuma EO, Villar J, Feng Y, et al. Fetal growth velocity standards from the Fetal Growth Longitudinal Study of the INTERGROWTH-21st Project. Am J Obstet Gynecol 2021;224:208.e1-18.