Antepartum heart rate patterns in small-for-gestational-age third-trimester fetuses: correlations with blood gas values obtained at cordocentesis.

Antepartum fetal heart rate records were made immediately before cordocentesis and blood gas analysis in 58 small- and 29 appropriate-for-gestational-age fetuses at 27 to 38 weeks' gestation. All appropriate-for-gestational-age fetuses had blood PO2 and pH values within the normal ranges for gestation, and in 27 of 29 cases the heart rate pattern was reactive; in two it was nonreactive. Abnormal heart rate patterns were present in 15 of the 19 small-for-gestational-age fetuses that were found to be hypoxemic, acidemic, or both. The abnormalities included decreased baseline variation, absence of accelerations, presence of decelerations, and increased baseline heart rate. A repetitive decelerative pattern best identified the hypoxemic fetuses. Fetal PO2 values in the lower normal range, present in many of the small-for-gestational-age fetuses, were in general associated with a reactive fetal heart rate pattern.