Reduced Growth in Non-Small for Gestational Age Fetuses from 35 Weeks of Gestation to Birth and Perinatal Outcomes

This study aimed to assess reduced fetal growth between 35 weeks of gestation and birth in non-small for gestational age fetuses associated with adverse perinatal outcomes (APOs).

It is a retrospective cohort study of 9,164 non-small for gestational age fetuses estimated by ultrasound at 35 weeks. The difference between the birth weight percentile and the estimated percentile weight (EPW) at 35 weeks of gestation was calculated, and we studied the relationship of this difference with the appearance of APO. APOs were defined as cesarean or instrumental delivery rates for nonreassuring fetal status, 5-min Apgar score <7, arterial cord blood pH <7.10, and stillbirth. Fetuses that exhibited a percentile decrease between both moments were classified into 6 categories according to the amount of percentile decrease (0.01-10.0, 10.01-20.0, 20.01-30.0, 30.01-40.0, 40.01-50.0, and >50.0 percentiles). It was evaluated whether the appearance of APO was related to the amount of this percentile decrease. Relative risk (RR) was calculated in these subgroups to predict APOs in general and for each APO in particular. Receiver operating characteristic and area under curves (AUC) for the difference in the percentile was calculated, used as a continuous parameter in the entire study population.

The median gestational age at delivery in uncomplicated pregnancies was 40.0 (39.1-40.7) and in pregnancies with APOs 40.3 (49.4-41.0), p < 0.001. The prevalence of APOs was greater in the group of fetuses with a decrease in percentile (7.6%) compared to those with increased percentile (4.8%) (p < 0.001). The RR was 1.63 (95% CI: 1.365-1.944, p < 0.001). Although the differences were significant in all decreased percentile groups, RRs were significantly higher when decreased growth values were >40 points (RR: 2.036, 95% CI: 1.581-2.623, p < 0.001). The estimated value of the AUC for percentile decrease was 0.58 (0.56-0.61, p < 0.001).

Fetuses with a decrease in the EPW between the ultrasound at 35 weeks of gestation and birth have a higher risk of APOs, being double in fetuses with a decrease of >40 percentile points.