Fetal Heart Rate Tracings and Adverse Outcomes among Term Small versus Appropriate for Gestational Age

This study aimed to compare the patterns of fetal heart rate tracings (FHRTs), and outcomes among individuals with small (birth weight [BW] <10% for gestational age [GA]; SGA) versus appropriate (BW at 10-89% for GA; AGA) newborns at term (≥37.0 weeks).

Our retrospective cohort study included consecutive deliveries over 15 months at a level IV center. FHRTs were reviewed by obstetricians blinded to maternal and neonatal outcomes. The inclusion criteria were non-anomalous singletons, cataloged as SGA or AGA birth weight using Alexander et al's nomogram. In 20-minute segments, the last 120 minutes of tracing were characterized. Rates of cesarean delivery (CD) and composite neonatal adverse outcomes (CNAOs) were compared.

Of 5,160 deliveries, 3,029 (58.7%) met the inclusion criteria, and among them, 422 (13.9%) were SGA and 2,607 (86.1%) AGA. There were no differences in FHRT baseline, variability, or accelerations. Compared to AGA, SGA was more likely to have prolonged decelerations (11.8 vs. 8.4%, p = 0.021), and recurrent decelerations with ≥50% of contractions (21.3 vs. 16.5%, p = 0.014). Overall, the presence of category II FHRT or not was similar between the SGA (91.2%) and AGA (88.5%; p = 0.097). Persistent category II FHRT was significantly more common among SGA (37.4%) than AGA (28.1%; aOR = 1.47; 95% CI: 1.47-1.82) newborns. The rate of CD for non-reassuring FHRT was similar among the two groups. CNAO occurred in 1.4% in both SGA and AGA neonates (p = 0.95).

In our cohort of those with fetal monitoring prior to delivery at ≥37 weeks, persistent category II FHRT at the end of labor was significantly more common in SGA compared to AGA neonates; however, composite neonatal morbidity did not differ between the two groups. Our analysis provides data for shared decision-making that among SGA newborns, abnormalities of FHRT are not linked with adverse outcomes.

· There were no differences in FHRT baseline, variability, or accelerations between AGA and SGA.. · SGA was more likely to have prolonged decelerations and recurrent decelerations with ≥50% of contractions.. · Persistent category II FHRT before delivery is significantly more common with SGA than AGA.. · FHRT abnormalities, however, were not associated with CD for non-reassuring FHRT, or adverse outcomes..