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In 2002, the National Institute of Child Health and Human Development (NICHD) proposed the 3-Tier fetal heart rate (FHR) classification system that was subsequently adopted by many organizations, categorizing tracings into three groups: Category I (normal), Category II (indeterminate), and Category III (abnormal). Recently, our podcast team received an interesting question form one of our podcast family members: “If there is a change in the fetal heart rate tracing intrapartum, but it is still in the normal range (like 120 going to 150)- and variability is normal, is that an abnormality? And what is meant by a ‘ZigZag’ FHT pattern (different than marked variability)?”. That is a fantastically complex question…and we will explain the answer in this episode.

1. Zullo F, Di Mascio D, Raghuraman N, Wagner S, Brunelli R, Giancotti A, Mendez-Figueroa H, Cahill AG, Gupta M, Berghella V, Blackwell SC, Chauhan SP. Three-tiered fetal heart rate interpretation system and adverse neonatal and maternal outcomes: a systematic review and meta-analysis. Am J Obstet Gynecol. 2023 Oct;229(4):377-387. doi: 10.1016/j.ajog.2023.04.008. Epub 2023 Apr 11. PMID: 37044237.

2. Ghi T, Di Pasquo E, Dall'Asta A, et al. Intrapartum Fetal Heart Rate Between 150 and 160 BPM at or After 40 Weeks and Labor Outcome.Acta Obstetricia Et Gynecologica Scandinavica. 2021;100(3):548-554. doi:10.1111/aogs.14024.

3. The 3 Tier System: chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://ncc-efm.org/filz/NICHD_Reference_from_CCPR.pdf

4. Jia YJ, Ghi T, Pereira S, Gracia Perez-Bonfils A, Chandraharan E. Pathophysiological Interpretation of Fetal Heart Rate Tracings in Clinical Practice. American Journal of Obstetrics and Gynecology. 2023;228(6):622-644. doi:10.1016/j.ajog.2022.05.023

5. Ghi T, Di Pasquo E, Dall'Asta A, et al. Intrapartum Fetal Heart Rate Between 150 and 160 BPM at or After 40 Weeks and Labor Outcome. Acta Obstetricia Et Gynecologica Scandinavica. 2021;100(3):548-554. doi:10.1111/aogs.14024.

6. Yang M, Stout MJ, López JD, Colvin R, Macones GA, Cahill AG. Association of Fetal Heart Rate Baseline Change and Neonatal Outcomes. Am J Perinatol. 2017 Jul;34(9):879-886. doi: 10.1055/s-0037-1600911. Epub 2017 Mar 16. PMID: 28301895.