FETAL HEART-RATE DECELERATIONS PRECEDE A DECREASE IN FETAL OXYGEN-CONTENT

To determine the relationship between abnormal fetal heart rate (FHR) patterns, fetal oxygen content by reflectance pulse oximetry, and the effects of maternal oxygen administration, 158 intrapartum women consi sting of 120 women with normal FHR patterns, and 38 women with varying degrees of variable FHR decelerations were examined. A new reflectanc e pulse oximetry probe was attached to the fetal forehead to continuou sly monitor fetal oxygen saturation (SpO(2)) during labor. Oxygen was administered for 30 min at 5 liters/min by nasal canula in 32 women. N o significant change in fetal SpO(2) was seen in women with normal FHR patterns, but a significant decline in SpO(2) was observed shortly be fore births. FHR decelerations less than 90 bpm occurred prior to the decline in fetal SpO(2). Maternal oxygen administration was effective in increasing fetal SpO(2) in fetuses with decreased SpO(2) (SpO(2) < 50%), but not in fetuses with high SpO(2) (SpO(2) > 60%). It is conclu ded that fetal SpO(2) exhibits no change during normal labor but signi ficantly declines shortly before birth, that relatively severe variabl e decelerations (<90 bpm) can decrease fetal SpO(2), and that maternal oxygen treatment at 5 liters/min is effective in augmenting fetal oxy gen tension in fetuses with decreased oxygen tension.