Association of Fetal Heart Rate Tracing with Adverse Neonatal Outcomes at 32^0/7 to 36^6/7 Weeks

Abstract

Objective

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.

Study Design

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.

Results

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%).

Conclusion

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.

Key Points

• 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.

Keywords

accelerations - hypoxic ischemic encephalopathy - intraventricular hemorrhage - minimal variability - mechanical ventilation - moderate variability - nonreassuring fetal heart rate tracing - preterm pregnancies - variable decelerations - 5-minute Apgar < 7

Publication History

Received: 29 September 2025

Accepted: 16 November 2025

Accepted Manuscript online:
18 November 2025

Article published online:
29 November 2025

• References

• 1 Chen HY, Chauhan SP, Ananth CV, Vintzileos AM, Abuhamad AZ. Electronic fetal heart rate monitoring and its relationship to neonatal and infant mortality in the United States. Am J Obstet Gynecol 2011; 204 (06) 491.e1-491.e10
• 2 American College of Obstetricians and Gynecologists. ACOG Practice Bulletin No. 106: Intrapartum fetal heart rate monitoring: nomenclature, interpretation, and general management principles. Obstet Gynecol 2009; 114 (01) 192-202
• 3 American College of Obstetricians and Gynecologists. Practice Bulletin No. 116: Management of intrapartum fetal heart rate tracings. Obstet Gynecol 2010; 116 (05) 1232-1240
• 4 Chauhan SP, Klauser CK, Woodring TC, Sanderson M, Magann EF, Morrison JC. Intrapartum nonreassuring fetal heart rate tracing and prediction of adverse outcomes: interobserver variability. Am J Obstet Gynecol 2008; 199 (06) 623.e1-623.e5
• 5 Cagino KA, Wiley RL, Roberts AW, Zullo F, Mendez-Figueroa H, Chauhan SP. Proportion of time in category II fetal heart rate tracing and adverse outcomes. Am J Perinatol 2025;
• 6 Zullo F, Di Mascio D, Raghuraman N. et al. Three-tiered fetal heart rate interpretation system and adverse neonatal and maternal outcomes: a systematic review and meta-analysis. Am J Obstet Gynecol 2023; 229 (04) 377-387
• 7 Wiley RL, Roberts AW, Cagino KA, Zullo F, Mendez-Figueroa H, Chauhan SP. Characteristics and categories of fetal heart rate tracings and adverse neonatal outcomes at term. Am J Perinatol 2025;
• 8 Patel S, Cagino KA, Roberts AW. et al. Fetal heart rate tracings and adverse outcomes among term small versus appropriate for gestational age. Am J Perinatol 2025;
• 9 Hurtado-Sánchez MF, Pérez-Melero D, Pinto-Ibáñez A, González-Mesa E, Mozas-Moreno J, Puertas-Prieto A. Characteristics of heart rate tracings in preterm fetus. Medicina (Kaunas) 2021; 57 (06) 528
• 10 Parer JTMDP, Ikeda T. A framework for standardized management of intrapartum fetal heart rate patterns. Am J Obstet Gynecol 2007; 197 (01) 26.e1-26.e6
• 11 Jaeschke R, Guyatt GH, Sackett DL. Users' guides to the medical literature. III. How to use an article about a diagnostic test. B. What are the results and will they help me in caring for my patients? The Evidence-Based Medicine Working Group. JAMA 1994; 271 (09) 703-707
• 12 Vandenbroucke JP, von Elm E, Altman DG. et al; STROBE Initiative. Strengthening the Reporting of Observational Studies in Epidemiology (STROBE): explanation and elaboration. Epidemiology 2007; 18 (06) 805-835
• 13 Timms D, Egan J, Smith K, Gurram P, Campbell W. 614: Does NICHD category II fetal heart rate tracing in the 30.  minutes prior to delivery predict fetal acidosis in preterm infants?. Am J Obstet Gynecol 2012; 206 (01) S276-S276
• 14 Krebs HB, Petres RE, Dunn LJ, Jordaan HV, Segreti A. Intrapartum fetal heart rate monitoring. I. Classification and prognosis of fetal heart rate patterns. Am J Obstet Gynecol 1979; 133 (07) 762-772
• 15 Holmes P, Oppenheimer LW, Gravelle A, Walker M, Blayney M. The effect of variable heart rate decelerations on intraventricular hemorrhage and other perinatal outcomes in preterm infants. J Matern Fetal Med 2001; 10 (04) 264-268
• 16 Henkel JE, Aziz MM, Reynolds CO, Goedecke PJ, Schenone MH. 763: Predicting fetal acidemia with continuous fetal monitoring in extreme preterm birth. Am J Obstet Gynecol 2019; 220 (01) S500-S500
• 17 Zanini B, Paul RH, Huey JR. Intrapartum fetal heart rate: correlation with scalp pH in the preterm fetus. Am J Obstet Gynecol 1980; 136 (01) 43-47
• 18 Matsuda Y, Maeda T, Kouno S. The critical period of non-reassuring fetal heart rate patterns in preterm gestation. Eur J Obstet Gynecol Reprod Biol 2003; 106 (01) 36-39
• 19 American College of Obstetricians and Gynecologists. ACOG Practice Bulletin operative vaginal delivery. Int J Gynaecol Obstet 2001; 74 (01) 69-76
• 20 Clark SLMD, Nageotte MPMD, Garite TJMD. et al. Intrapartum management of category II fetal heart rate tracings: towards standardization of care. Am J Obstet Gynecol 2013; 209 (02) 89-97
• 21 American College of Obstetricians and Gynecologists. Informed consent and shared decision making in obstetrics and gynecology: ACOG Committee Opinion, Number 819. Obstet Gynecol 2021; 137 (02) e34-e41
• 22 Weissbach T, Heusler I, Ovadia M. et al. The temporal effect of Category II fetal monitoring on neonatal outcomes. Eur J Obstet Gynecol Reprod Biol 2018; 229: 8-14
• 23 ACOG Committee on Obstetric Practice. ACOG Committee Opinion No. 348, November 2006: umbilical cord blood gas and acid-base analysis. Obstet Gynecol 2006; 108 (05) 1319-1322
• 24 Ananth CV, Joseph KS, Oyelese Y, Demissie K, Vintzileos AM. Trends in preterm birth and perinatal mortality among singletons: United States, 1989 through 2000. Obstet Gynecol 2005; 105 (5 Pt 1): 1084-1091
• 25 Ananth CV, Vintzileos AM. Maternal-fetal conditions necessitating a medical intervention resulting in preterm birth. Am J Obstet Gynecol 2006; 195 (06) 1557-1563
• 26 Blackwell SC, Grobman WA, Antoniewicz L, Hutchinson M, Gyamfi Bannerman C. Interobserver and intraobserver reliability of the NICHD 3-tier fetal heart rate interpretation system. Am J Obstet Gynecol 2011; 205 (04) 378.e1-378.e5