Clinical significance of fetal heart rate patterns during labor IX: prolonged pregnancy

The intrapartum FHR and UC were recorded in a population of 707 consecutive cases of prolonged gestation looking for a characteristic pattern. There is no typical pattern for prolonged pregnancy. However, there are differences from preterm and term populations. There is a very high incidence of variable (55%) and late (17%) decelerations. These were seen more frequently among cases receiving oxytocin. Nearly 50% of C-sections had lates. Baseline alterations (tachycardia 26%, fixed 8%, and saltatory 17%) were often associated. Apgar scores < or = 6 at 1 minute were correlated with variable and late decelerations. However, acidemia (UA pH < or = 7.20) could not be predicted from FHR patterns because there was no correlation between low pH and clinical depression. Alarmingly a few fetuses in agonal state presented normal appearing tracings, or deteriorated rapidly without the usual indicative changes by FHR. All intrapartum or NND had this misleading pattern. In view of this unpredictable aberrant pattern as the only certain means to prevent these deaths, it is suggested that no pregnancy should be allowed to reach 294 days post LMP.