Antenatal detection of large-for-gestational-age fetuses following implementation of the Growth Assessment Protocol: secondary analysis of a randomised control trial

Objective: To determine whether the Growth Assessment Protocol (GAP) affects the antenatal detection of large for gestational age (LGA) or maternal and perinatal outcomes amongst LGA babies.

Design: Secondary analysis of a pragmatic open randomised cluster control trial comparing the GAP with standard care.

Setting: Eleven UK maternity units.

Population: Pregnant women and their LGA babies born at ≥36⁺⁰ weeks of gestation.

Methods: Clusters were randomly allocated to GAP implementation or standard care. Data were collected from electronic patient records. Trial arms were compared using summary statistics, with unadjusted and adjusted (two-stage cluster summary approach) differences.

Main outcome measures: Rate of detection of LGA (estimated fetal weight on ultrasound scan above the 90th centile after 34⁺⁰ weeks of gestation, defined by either population or customised growth charts), maternal and perinatal outcomes (e.g. mode of birth, postpartum haemorrhage, severe perineal tears, birthweight and gestational age, neonatal unit admission, perinatal mortality, and neonatal morbidity and mortality).

Results: A total of 506 LGA babies were exposed to GAP and 618 babies received standard care. There were no significant differences in the rate of LGA detection (GAP 38.0% vs standard care 48.0%; adjusted effect size -4.9%; 95% CI -20.5, 10.7; p = 0.54), nor in any of the maternal or perinatal outcomes.

Conclusions: The use of GAP did not change the rate of antenatal ultrasound detection of LGA when compared with standard care.