Neonatal morbidity following resolution of fetal growth restriction diagnosed at second-trimester anatomy ultrasound.

BACKGROUND

Fetal growth restriction (FGR) diagnosed in mid-pregnancy is associated with substantial perinatal risk. However, the prognostic significance of FGR identified at the time of the second-trimester anatomy ultrasound that subsequently resolves later in pregnancy remains incompletely understood.

OBJECTIVES

To evaluate the association between early FGR with subsequent growth normalization and severe neonatal morbidity (SNM), and to compare neonatal outcomes across pregnancies with persistent early FGR, resolved early FGR, and normal fetal growth.

STUDY

DESIGN

This retrospective cohort study included singleton pregnancies that underwent a routine second-trimester fetal anatomy ultrasound between 18 weeks 0 days and 23 weeks 6 days of gestation and had one or more follow-up third-trimester ultrasound examinations with fetal biometry performed at 28 weeks' gestation or later, delivering at two tertiary care hospitals in New York between January 2019 and December 2023. FGR was defined as estimated fetal weight or abdominal circumference <10th percentile. Pregnancies with FGR first diagnosed after 24 weeks' gestation were excluded. Pregnancies were categorized into three groups: no FGR, early FGR that persisted into the third trimester (persistent early FGR), and early FGR that subsequently normalized (resolved early FGR), with classification based on the last third-trimester ultrasound with fetal biometry performed prior to delivery. The primary outcome was SNM, defined as a composite of life-threatening neonatal diagnoses and procedures. Secondary outcomes included respiratory distress syndrome (RDS), neonatal intensive care unit (NICU) admission, preterm birth, need for parenteral nutrition, and need for phototherapy. Multivariable logistic regression was used to estimate adjusted odds ratios (aORs) controlling for demographic and clinical covariates.

RESULTS

Among 20,022 pregnancies, 636 (3.2%) were diagnosed with early FGR at the mid-pregnancy anatomy ultrasound, of which 181 (28.5%) subsequently demonstrated resolution and 455 (71.5%) remained persistent. Compared with pregnancies without FGR, resolved early FGR was associated with increased odds of SNM (aOR 1.80, 95% CI, 1.10-2.83), RDS (aOR 3.30, 95% CI, 1.01-8.90), preterm birth (aOR 2.04, 95% CI, 1.18-3.34), and need for parenteral nutrition (aOR 3.66, 95% CI, 1.71-7.17). NICU admission and phototherapy did not differ significantly. Persistent early FGR was associated with increased odds of SNM and secondary outcomes. Neonatal risk followed a graded pattern across groups, with lowest risk among pregnancies without FGR, intermediate risk among those with resolved early FGR, and highest risk among those with persistent early FGR, with findings largely reflecting respiratory and prematurity-related morbidity.

CONCLUSIONS

FGR diagnosed at the time of the second-trimester anatomy ultrasound is associated with increased neonatal morbidity even when fetal growth subsequently normalizes. Resolution of early FGR is associated with reduced but persistent risk, supporting consideration of early FGR as a marker of residual neonatal vulnerability. Further prospective studies are needed to refine risk stratification and determine whether specific management strategies modify outcomes in pregnancies complicated by early FGR with subsequent growth normalization.