Intrapartum fetal monitoring in preterm deliveries: prospective study.

Fetal heart rate (FHR) and fetal acid-base status were prospectively studied in 61 patients in preterm labor of unknown etiology. Tachycardia (43%), decreased variability (39%), and variable decelerations (61%) were often recorded. Fetal acidosis (pH less than 7.25 in scalp blood) occurred in 52% of patients delivered in weeks 28 to 33 and in 8% of patients delivered in weeks 34 to 36 of gestation. Ominous FHR changes considered classic for fetal distress were very frequently associated with fetal acidosis, but among the most immature infants with fetal acidosis several had tachycardia and decreased variability combined with variable decelerations of innocent appearance. Patients treated with a beta-receptor agonist (terbutaline) for inhibition of preterm labor had fetal tachycardia and decreased variability more often than nontreated patients. No positive correlation with fetal acidosis for these FHR changes could be demonstrated in the terbutaline-treated patients. The results indicate that fetal acidosis can appear rapidly and frequently among the most immature infants during labor, and emphasize the value of considering the gestational age and the administration of beta-receptor stimulators in the assessment of the FHR pattern in preterm labor.