J. biosoc. Sci. (1991) 23, 417-423 BIRTHWEIGHT AND SOCfOBIOLOGICAL FACTORS IN ILORIN, NIGERIA EHIGIE EBOMOYI*, OLALEKAN O. ADETOROf AND ANANDA R. WICKREMASINGHE* ^Department of Applied Health Sciences, Tulane University, New Orleans, USA, and tDepartment of Obstetrics and Gynaecology, University of Ilorin Teaching Hospital, Nigeria Summary. Social and biological factors influencing birthweight of 3053 Ilorin babies were studied. The mean birth weights were 2-998 kg ± 0-133 (SD) for males and 2-932 kg ±0.154 (SD) for females. Multiple regression analysis showed that maternal weight, height, age, education and ethnicity, and child's sex, significantly affected birthweight of infants. Some quadratic and interaction terms also contributed significantly to the prediction of birthweight. The strategies to control the incidence of low birth weight are discussed. Introduction Birthweight is not only a reliable index of intrauterine growth but also a determi- nant of the probability that the infant will survive and experience normal develop- ment, especially in the developing countries where low birthweight is a major factor in the high infant mortality. The World Health Organization Expert Com- mittee on Maternal and Child Health (1975) endorsed the international definition of low birthweight infants as weighing 2-5 kg or less at birth. This definition has been adopted in this study. Of the several studies of birthweight in Nigeria, most relate to the south, par- ticularly Ibadan, Lagos and Calabar (Oduntan, Odunlami & Ayeni, 1977; Watt 1959; Morley & Knox, 1960; Ogun & Okorafor, 1985), though Kwara State is less known. In northern Nigeria, data on the distribution and correlates of birth- weight are few (Rehan & Tafida, 1979; Osuhor, 1976). The recognised variation of birthweight among different ethnic groups warrants the development of specific international and local standards. This study was therefore undertaken to examine the distribution of birthweight in Ilorin, the capital city of Kwara State, Nigeria, and to investigate the effects on it of maternal age, weight, parity, height, educa- tion and occupation, and child's sex. Materials and methods Kwara is one of the twenty-one states of the Federal Republic of Nigeria. In 1980, the estimated population of Ilorin was 477,564 (Oni, 1986), and that of 417