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Clinical, scientific and ethical aspects of fetal and neonatal care at extremely preterm periods of gestation

As defined by the World Health Organization in 1972, preterm delivery is delivery which occurs before 37 weeks of gestation; it accounts for 6% to 10% of all deliveries, depending on the demographic features of the population examined'. The overall preterm delivery rate is determined after consideration of all causes of spontaneous preterm labour and deliberate intervention to achieve elective delivery. It is therefore caused by a heterogenous group of disorders occurring in pregnancy of which a significant proportion are of unknown aetiology and poorly defined pathophysiology (e.g. spontaneous preterm labour, pre-eclampsia, intrauterine growth restriction, chorioamnionitis). The majority of centres now report close to 100% survival for infants born after 32 weeks of gestation, and hence it is delivery before this time that is of major perinatal importance. After 27 weeks of gestation intact survival exceeds 50% and, while short and long term morbidity are a significant concern, there is general agreement on the provision of aggressive fetal and neonatal care with a clear objective to achieve survival with the optimal quality of life. At extremely preterm periods of gestation (i.e. < 27 weeks), or what is sometimes referred to as the margin of viability, the prognosis is sometimes so poor that the objectives are far from clear and the decisions regarding management difficult for the parents, the obstetrician and the neonatal physician. There is no clear definition of the lower limit of preterm, but the International Classification of Diseases describes the perinatal period as beginning at 22 completed weeks at a time when the birthweight is approximately 500 g. In practical terms, the accepted lower limit of viability may vary from one hospital and physician to the next but generally lies somewhere between 23 and 25 weeks of gestation; there are a small number of cases reported in the literature describing survival at 22 weeks. While specific cases of nonresuscitation have been tested in British courts there are no clear guidelines on this issue. This review will concentrate on the clinical, scientific and ethical aspects of perinatal care at these extremely preterm periods of gestation (23+O to 26'6 weeks). The extent of the problem