Uncomplicated Baseline Fetal Tachycardia or Bradycardia in Postterm Pregnancies and Perinatal Outcome

ABSTRACT

Objective: to assess perinatal outcome in post-term pregnancies in which fetal heart rate (FHR) monitoring revealed either uncomplicated baseline fetal tachycardia (> 160 bpm) or fetal bradycardia (≤ 120 bpm).

Study Design: We performed a case-control study of patients who underwent fetal assessment between July 1989 and June 1995, as part of post-term evaluation. Inclusion criteria consisted of nonlaboring afebrile patients with singleton post-term pregnancies ≥ 41 weeks of gestation by strict dating criteria (last menstrual period consistent with ultrasound biometric parameters obtained prior to 20 weeks' gestation), normal fetal anatomy, intact membranes, and reactive nonstress test with no evidence of chorioamnionitis. Patients with fetal tachy or brady arrhythmias, FHR decelerations, or loss of short-term beat-to-beat variability were excluded. Baseline FHR was recorded retrospectively by an observer blinded to maternal and neonatal clinical outcome. For each case of uncomplicated baseline fetal tachycardia (≥ 160 bpm) or bradycardia (≤ 120 bpm), either two or three control cases (matched for maternal age and parity), with FHR > 120 bpm and < 160 bpm, were identified. Outcome variables assessed included: incidence of cesarean delivery, nuchal cord at delivery, meconium-stained amniotic fluid (AF), 5-min Apgar score < 7, fetal growth restriction (< 10th per-centile for 41 weeks' gestation), meconium aspiration syndrome, and neonatal intensive care unit (NICU) admission. Statistical analysis included two-tailed t-test and χ² test when appropriate, with p < 0.05 considered significant throughout.

Results: During the study period 1390 post-term patients (6.81% of the general population) were assessed. Of these, 31 (2.23%) fetuses exhibited baseline FHR ≥ 160 bpm, and 76 fetuses (5.46%) exhibited baseline FHR ≤ 120 bpm. No significant differences were noted in the incidence of cesarean delivery, presence of nuchal cord at delivery, meconium-stained AF, 5-min Apgar scores < 7, fetal growth restriction, meconium aspiration syndrome, or the incidence of NICU admissions between the groups of patients with fetal tachycardia, bradycardia, and their respective controls.

Conclusions: Uncomplicated baseline fetal tachycardia or bradycardia in post-term patients are not associated with an increase in the incidence of adverse perinatal outcome.

Keywords

Post-term - electronic fetal monitoring - fetal heart rate - tachycardia - fetal bradycardia - perinatal outcome