Fetal response to voluntary maternal hyperventilation. A preliminary report.

Maternal hyperventilation can cause transient reduction in fetal oxygen tension. Fifty women with normal and high-risk pregnancies, between the 32nd and 43rd week, were voluntarily hyperventilated; in 33, fetal heart rate (FHR) acceleration or transient tachycardia were observed (reactive FHR). Of the 33 pregnancies the outcome was good in 30 (91%) as judged by the absence of perinatal death, no fetal distress in labor and no intrauterine growth retardation (IUGR). In 14 patients in whom there was no FHR response to maternal hyperventilation (non-reactive FHR), the outcome of pregnancy was significantly worse; one infant died neonatally, 10 were either chronically (IUGR), or acutely distressed. Only in 3 was the outcome good (21%). The study showed that there is good correlation between a "reactive" FHR and favorable neonatal outcome, and between a "non-reactive" FHR and an unfavorable neonatal outcome.