Cerebral handicap in full-term neonates related to the mechanical forces of labour.

Sometimes the relationship between peripartum events and neonatal CNS injury is obvious: for example, following complete abruptio placentae or umbilical cord prolapse and occlusion with a delay of many minutes before delivery of the baby. These circumstances are, of course, rare in modern obstetrics. Usually, when a neonate develops neurological injury, a host of various potentially adverse peripartum factors are assumed to be the aetiology, but without definitive evidence. Among these latter factors are those we have focused on in this paper: the mechanical forces exerted on the fetal head during labour when the full-term fetus is in cephalic presentation. The mechanical events during the first stage of labour are reviewed, showing how uterine contractions result in cervical dilatation and descent and rotation of the fetal head. The consequences of these forces on the fetal intracranial pressure and blood flow are discussed: FHR remains normal up to a certain pressure threshold, above which decelerations occur. In other words, excessive pressures applied to the fetal head, either spontaneously (e.g. uterine tetany) or iatrogenically (e.g. traumatic forceps delivery or excessive fundal pressure) can increase fetal intracranial pressure to such a degree as to result in significant decreases in cerebral blood flow that are associated with fetal heart rate decelerations. Even when decelerations are simultaneous to contractions, decelerations cannot be considered as reflex and innocuous, as they are indeed associated with a decreasing cerebral blood flow. They must therefore be considered and evaluated in the management of labour. Cord compression and functional modifications of intervillous space by mechanical forces may further compromise the biological status of the fetus, leading to severe asphyxia. Neurological evaluation of the neonate within the first few days after delivery is currently the only way to provide the obstetricians with information on the possible consequences of an abnormal labour. The assessment of normality of the CNS in the neonate born at term, and its value in predicting late outcome are discussed. When abnormalities are detected after one or repeated assessments, abnormal neurological signs and symptoms are classified into three grades at the end of the first week. According to our data, a good correlation exists between this neonatal grading of cerebral dysfunction and late outcome. A careful evaluation of fetal head deformation, extensive caput succedaneum, and extensive retinal haemorrhages can help to interpret an abnormal labour retrospectively.(ABSTRACT TRUNCATED AT 400 WORDS)