The Pre-term Baby

Abstract

Babies who weigh 2,500 g (5 lb 8 oz) or less at birth present special problems in the newborn period, and though (in the United Kingdom) these babies constitute only 7% of all newborns, about half the total neonatal deaths occur in this group. It used to be an internationally agreed convention to classify all babies weighing 2,500 g or less at birth as “premature.” Nevertheless, it has been increasingly recognized in the past 10 years that not all of them are born prematurely—that is, after an abnormally short gestation. There are, in fact, two major categories of low-birth weight baby—the pre-term baby and the small-for-dates baby—and they differ not only in the cause of their low birth weight but also in the clinical problems they encounter in the perinatal period. Pre-term babies are those born before 37 completed weeks from the first day of the mother's last menstrual period. In the United Kingdom they comprise about two-thirds of low-birth weight babies and their clinical problems may largely be accounted for by immaturity and unreacliness to adapt to life outside the uterus. Small-for-dates babies are those whose birth weight is abnormally low for the gestational age at which they are born. The definition of low birth weight for gestation is necessarily an arbitrary one, but there is now a fair measure of agreement for describing babies whose birth weight is below the 10th centile of birth weight for their gestational age as small for dates. These babies constitute about one-third of low birth weight babies in the United Kingdom. Many of their problems, which differ from those of the pre-term babies, may be explained by intrauterine undemutrition. It is, of course, possible for a low birth weight baby to be both pre-term and small-for-dates. Table I summarizes the differences between these two classes of low birth weight babies. The remainder of this article describes the problems of the pre-term baby; the second article describes those of the small-for-dates baby and discusses the present day outlook for low birth weight babies. © 1971, British Medical Journal Publishing Group. All rights reserved.