A CENTILE CHART FOR BIRTH-WEIGHT FOR AN URBAN-POPULATION OF THE WESTERN CAPE

Evidence from large epidemiological studies has supported concern that being born light for gestational age (LiGA) may be detrimental. The i ncidence of LiGA babies is an important indicator of the health of wom en of reproductive age in deprived communities. In the assessment of L iGA in the Western Cape, centile charts constructed for populations in other parts of the world are generally used, These charts, however, m ay not be appropriate. Patients residing in the area served by the Tyg erberg Hospital obstetric service, who booked early with singleton pre gnancies, had their gestational age confirmed by early ultrasound and delivered between 1 March 1989 and 28 February 1990 were included in t he study. The sample consisted of 3 643 patients. The mean birth weigh t was 2 995 g (SD 573 g) and the range 760 - 5 080 g. The distribution of birth weight at each week of gestation from 28 to 42 weeks was not normal. The 4-parameter Johnson family of densities was used to model the distribution of birth weight at each gestational age. A compariso n of the distribution of birth weight in the study relative to the per inatal growth chart for international reference constructed by Dunn wa s also made. In addition to considering an overall chart, the sample w as subdivided according to a number of characteristics (e.g. gender, f irstborn and latter-born babies, smoking habit, hypertensive disorders and induction of labour) in order to explore their impact on the dist ribution of birth weight. Having explored the potential impact of all these factors, it was concluded that a single chart including all pati ents could be constructed.