Ante- and intrapartum assessment of the fetus

Abstract

Despite widespread use of fetal assessment techniques, it is not always possible to detect fetal compromise at an early stage before permanent damage has occurred or to intervene effectively to prevent or ameliorate fetal damage. The only intervention that can ‘rescue’ the fetus from an adverse intrauterine environment is delivery, which may result in death or disability from prematurity. Delivery should be undertaken just before fetal compromise becomes permanent damage, but current assessment techniques do not predict this point accurately. Thus, some fetuses are delivered more prematurely than necessary and others delivered after they are irreversibly damaged. In the antepartum period various measurements are used to provide an overall impression of fetal health. The simplest is asking the mother whether the baby is moving well. Ultrasound scanning is commonly used. Electronic fetal heart rate (FHR) monitoring to produce a cardiotocograph (CTG) is widely available, though research does not support its use in the antepartum period. Whatever the method used, effective assessment depends on the background risk in the pregnancy. The aim of intrapartum FHR monitoring is to identify fetuses that become hypoxic and acidotic during labour so that delivery can be expedited. Interpretation of the CTG is explained. A suspicious CTG requires further investigation or delivery. Once the cervix has dilated beyond 3 cm a sample of fetal scalp blood can be analysed for pH and base deficit. After birth, if the neonate shows signs of compromise, blood from the umbilical cord can be analysed for pH, base deficit and partial pressure of carbon dioxide.