Effect of Growth Restriction on Fetal Heart Rate Patterns in the Second Stage of Labor.

Objective: We aimed to estimate the effect of intrauterine growth restriction (IUGR) on electronic fetal monitoring (EFM) patterns in the second stage of labor.

Study Design: We performed a 5-year retrospective cohort study of consecutive singleton, non-anomalous, term gestations. We compared IUGR infants, those with a birth weight less than the 10th percentile, with non-IUGR infants, those greater than or equal to the 10th percentile. Our primary outcome was the EFM patterns in the 30 minutes before delivery. A secondary analysis was performed excluding infants with composite morbidity. Logistic regression was used to adjust for body mass index, race, nulliparity, induction, and protracted labor.

Results: Out of the 5,388 infants, 652 (12.1%) were IUGR. IUGR fetuses had less accelerations (29.0 vs. 35.9%, p < 0.01), even among apparently normal infants (29.0 vs. 36.4%, p < 0.01). IUGR fetuses had a higher risk of decelerations, and in all, IUGR accounted for 6% of late decelerations (attributable risk 0.06, 95% confidence interval 0.02-0.10). There was no significant association between IUGR and bradycardia or minimal variability.

Conclusion: Growth restriction at term confers an increased risk of late decelerations, even in the absence of neonatal morbidity. EFM patterns may require different interpretations based on a priori risk and clinical factors.