Should Fetal Growth Charts Be References or Standards?

Area of Science:

• Perinatology
• Fetal Medicine
• Obstetrics

Background:

• Fetal growth standards, derived from low-risk pregnancies, are theoretically superior for monitoring fetal growth compared to conventional references.
• This study investigates the impact of altering chart inclusion criteria on the resulting fetal growth curves.

Purpose of the Study:

• To compare estimated fetal weight (EFW) distributions between a reference chart and a standard chart derived from a hospital's routine 32-week ultrasounds.
• To assess how modifying inclusion criteria for fetal growth charts influences the classification of fetuses as small for gestational age.

Main Methods:

• Summarized EFW distributions from 2309 nonanomalous singleton fetuses at 32 weeks gestation.
• Compared a reference group (all nonanomalous fetuses) with a standard group (fetuses without maternal-fetal conditions affecting growth).
• Calculated 3rd, 5th, 10th, and 50th percentile EFWs and the proportion of small-for-gestational-age fetuses for both charts.

Main Results:

• Only 30% (690/2309) of the reference fetuses met the standard's inclusion criteria.
• No significant differences were observed in EFW distributions between the reference and standard curves (e.g., 50th percentile: 1989g vs. 1968g; 10th percentile: 1711g vs. 1710g).
• The proportion of fetuses classified as small for gestational age was identical (9.9%) for both the reference and standard charts.

Conclusions:

• In this study, there was little practical difference between using a fetal growth reference or a standard for detecting small-for-gestational-age infants.
• The findings suggest that modifications in chart inclusion criteria may not substantially alter the clinical utility of fetal growth monitoring tools.