A retrospective study of 1145 pregnant women showed that trends in mean maternal weight gain from the time of booking until delivery were not linear. Statistically significant lower rates of maternal weight gain were seen before 16 weeks, after 36 weeks and between 28 and 32 weeks gestation (P less than 0.05). The mean maternal weight gain was 10.71 kg (SD 4.3) and the mean weekly weight gain was 0.38 kg (SD 0.16). A wide variation of maternal weight gain was seen in women with a normal outcome. The mean weight gain in heavy (greater than 68 kg) and light (less than 55.4 kg) women was less than that in women whose weight was in the third quartile (60-68 kg, P less than 0.05). The mean maternal weight gain was less in young (less than 20 years) women than in older women (greater than 25 years; P less than 0.05), less in parous than in primigravid women from week 37 onwards (P less than 0.05), less in smokers than in non-smokers from 20 weeks onwards (P less than 0.05), and greater in hypertensive women (BP less than 140/90) than in normotensive women (P less than 0.05) from week 24 onwards. The mean weight gain in women who had small for gestational age (SGA) infants was not significantly different from that in women who had infants that were of appropriate size for gestational age. After taking into account infant and placental weight using multiple regression analysis, the factors that were associated with statistically significant differences in average weekly weight gain were parity, body mass index, smoking habit and raised blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)