(1256) Fetal heart tracings with and without uterine rupture during trial of labor after cesarean

ICD codes were used to identify TOLAC UR cases and controls of singleton patients in a multi-hospital system from 2013 – 2025. Medical eligibility for TOLAC, intent to TOLAC and presence of ≥ 60 minutes of FHT for analysis was confirmed by chart review. Obstetricians blinded to maternal characteristics and UR outcome reviewed and quantified FHTs using standardized definitions per the American College of Obstetricians and Gynecologists. FHTs were reviewed in four 10-minute time periods: admission, 60, 30 and 10 minutes prior to delivery.  Either chi-square or Fisher’s exact test, as appropriate, were used to compare patient attributes and FHT characteristics across the UR and control groups.


Results:

Of 142 UR cases, 77 were included and compared to 70 controls (total analytic cohort n=147). There was no significant difference in mean gestational age at delivery.  UR cases were less likely to be advanced maternal age (p=.003) or have a previous vaginal delivery (p=.006) (Table 1).  There were no significant differences in FHT measures on admission or at 60 minutes prior to delivery between groups. At 30 minutes, UR cases were more likely to have late decelerations (p=.02) compared to controls. At 10 minutes prior to delivery, cases were more likely to have an abnormal baseline (p=.006) and less contractions (p=.006) (Figure 1).


Conclusion:
FHT differences preceding UR in patients undergoing TOLAC may be subtle and dynamic. Notably, there was no difference in variable decelerations across cases and controls, contrary to common teachings. Cases were more likely to have late decelerations at 30 minutes prior to delivery, but this difference did not persist in the final 10 minutes of labor. Our observed UR FHT characteristics during the final 10 minutes of labor, possibly indicating loss of uterine tone and fetal distress, suggest clinically significant FHT changes may not be evident until uterine rupture occurs.