Fetal Growth Velocity Standards from the Fetal Growth Longitudinal Study of the INTERGROWTH-21st Project.
Ohuma EO., Villar J., Feng Y., Xiao L., Salomon L., Barros FC., Ismail LC., Stones W., Jaffer Y., Oberto M., Noble JA., Gravett M., Qingqing W., Victora CG., Lambert A., Di Nicola P., Purwar M., Bhutta ZA., Kennedy SH., Papageorghiou AT., International Fetal and Newborn Growth Consortium for the 21(st) Century (INTERGROWTH-21(st) Project) None.
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 towards preventing impaired growth. OBJECTIVE: 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: Prospective, longitudinal study of 4,321 low-risk pregnancies from eight 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 (HC), biparietal diameter (BPD), occipitofrontal diameter (OFD), abdominal circumference (AC) and femur length (FL) 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 modelled using fractional polynomial regression. RESULTS: Peak velocity was observed at a similar gestational age: 16- and 17-weeks' gestation for HC (12.2 mm/week), and 16 weeks' gestation for AC (11.8 mm/week) and FL (3.2 mm/week). However, velocity growth slowed down rapidly for HC, BPD, OFD and FL, with an almost linear reduction towards term that was more marked for FL. Conversely, AC velocity remained relatively steady throughout pregnancy. The change in velocity with gestational age was more evident for HC, BPD, OFD and FL than for AC 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 wellbeing comprehensively worldwide. Fetal growth velocity curves may be valuable if one wants to study the pathophysiology of fetal growth. We provide an App that can easily be used 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 App is freely available with the other INTERGROWTH-21st tools at (https://intergrowth21.tghn.org/standards-tools/).