Effect of serial ultrasound scans and optimized fetal weight limits on
reduction of stillbirth risk: population-based cohort study
Abstract
Objective: To assess the effect of serial growth scans and optimised
fetal weight limits on the risk of stillbirth in low and high-risk
maternity populations. Design: Retrospective cohort study Setting:
United Kingdom 2015-2020 Population: 1,572,817 singleton pregnancies
cared for in maternity units that have implemented the Growth Assessment
Protocol (GAP). Methods: Analysis of fully anonymised, prospectively
recorded core data from 132 National Health Service institutions.
Stillbirth rate and relative risk was assessed according to risk status
assigned at booking. We constructed receiver operator curves (ROC) and
determined area under the curve (AUC) and optimal centile points using
Youden’s Index. Main Outcome: Rate of stillbirth from 24 weeks
gestation. Results: The overall cohort included 6569 stillbirths (rate
per thousand: 4.18). The rate was higher in pregnancies that had been
designated high risk (6.23) than low risk (3.61; RR 1.7, CI 1.6-1.8).
High risk pregnancies that did not receive monitoring by serial
ultrasound had a stillbirth rate that was more than twice as high than
those that did get serial scans as per protocol (11.94 vs 5.64). The
optimal centile point for predicting stillbirth was 11.3 for the overall
cohort (sensitivity 36.8, specificity 84.1 and AUC 62.3%), 15.2 for low
risk pregnancies (sensitivity 35.1, specificity 84.6, AUC 61.3%) and
2.7 for high risk pregnancies (sensitivity 34.2, specificity 88.9, AUC
61.2% ). Conclusions: Serial third trimester growth scans can halve
stillbirth risk in pregnancies designated high risk. Optimal fetal size
limits for antenatal surveillance are specific to the risk status of
pregnancy.