Association of Fetal Heart Rate Tracing with Adverse Neonatal Outcomes at 320/7 to 366/7 Weeks

The objective of this study is to determine if patterns of fetal heart rate tracings (FHRT) were associated with an increased rate of composite adverse neonatal outcomes (CANO) among preterm deliveries at 32^0/7 to 36^6/7 weeks.

This was a retrospective review of intrapartum FHRT between 20 and 120 minutes before birth, among nonanomalous singletons delivered at 32^0/7 to 36^6/7 weeks. The study was conducted at a Level IV maternal center during a consecutive 15-month period. Obstetricians reviewing FHRT were blinded to the maternal characteristics, intrapartum course, and neonatal outcomes. FHRT patterns were categorized based on time spent in the final 2 hours before delivery (<50 vs. ≥50%). The primary outcome was the CANO, which included any of the following: 5-minute Apgar < 7, mechanical ventilation > 6 hours, umbilical artery pH < 7.00, bronchopulmonary dysplasia, interventricular hemorrhage, necrotizing enterocolitis, neonatal seizures, neonatal confirmed sepsis, hypoxic ischemic encephalopathy, birth injury, meconium aspiration syndrome, or neonatal death.

Of 5,160 patients, 672 (13%) met the inclusion criteria. CANO occurred in 57 (8.5%) newborns. Overall, FHRT patterns that differed significantly between those without versus with CANO included minimal variability (8.8 vs. 19.3%, p = 0.01, PLR = 2.2 [positive likelihood ratio], PPTP 17% [positive posttest probability]), moderate variability (76.4 vs. 52.6%, p < 0.001, NLR = 2.01 [negative likelihood ratio], NPTP 15.7% [negative posttest probability]), accelerations (58.4 vs. 40.4%, p = 0.009, NLR = 1.43, NPTP = 11.7%), and severe variable decelerations (3.5% p = 0.003, PLR = 10.79, PPTP = 50.1%). Category III FHRT pattern was also associated with an increased posttest probably of CANO (0.3 vs. 1.8%, p = 0.12, PLR = 5.39, PPTP = 27%).

While moderate variability and accelerations were associated with significantly lower likelihood of CANO among newborns delivered at 32^0/7 to 36^6/7 weeks, minimal variability and severe variable decelerations were significantly more common in preterm newborns with CANO.

· At 32 to 36 weeks, CANO occur in approximately 8% of neonates.. · Severe variable decelerations and minimal variability increase risk of CANO.. · The PPTP of CANO is 33%, if Category III FHRT is noted before birth.. · The PPTP is 13%, if there is persistent Category II FHRT in the last 120 minutes..