Intrapartum evaluation of the fetus

The preliminary estimate of total births in the USA for 2005 was 4,138,349. Intrapartum fetal heart-rate (FHR) monitoring was used in more than 85% of the deliveries. Fetal heart-rate monitoring was introduced into clinical practice in the 1970s. At that time, obstetric providers and researchers in fetal physiology believed electronic fetal monitoring (EFM) would identify changes in the FHR and/or rhythm that reflect fetal acidosis. It was presumed that detection would be early enough to allow clinical intervention that would prevent perinatal asphyxia. Despite 30 years of widespread use and multiple randomized clinical trials, FHR monitoring has not yet been shown to decrease perinatal mortality other than by decreasing intrapartum fetal deaths. Moreover, some experts believe that the use of EFM leads to over-detection of non-reassuring FHR patterns, thereby directly contributing to the escalating rate of cesarean-section deliveries in the USA, which by 2005 increased to 30.3%. We will review the physiology underlying FHR patterns, and the possible reasons why randomized trials of EFM have so far failed to demonstrate efficacy. The current knowledge that guides interpretation of EFM in the intrapartum period will be discussed, with special emphasis on newer methods for intrapartum fetal surveillance.