Teenage pregnancies lower average birthweight. In the NBS, teenage mothers had significantly lower average birthweight of 2 920 +/- 553 g compared with 3 133 +/- 533 g among women in the general population. A high rate of LBW on the infants of the teenage mothers was the significant factor in lowering the average birthweight. In both NBS and the PMHS the incidence of LBW 18% and 15% respectively as well as the rate of preterm delivery of 24% and 23% respectively were high. In PMHS although the numbers were small, the incidence of LBW was high (13%) in the 14-year-olds and in the 15-year-olds it was 4.8% which was much lower than that for 17- and 18-year-olds. In a large series in Nigeria the incidence of LBW was 27% in mothers aged less than 15 years, 26% in mothers aged 15-19, 20% in those aged 20-24 and least (18%) in the 25-29 year age group. Many unfavourable socioeconomic circumstances and lack of adequate antenatal supervision contribute to these high rates. Some of the teenage mothers-particularly the very young, below 16 years-are physically immature and are still growing children themselves. Their nutrient intake is shared between their own growth needs and those of their foetuses. In the Nigerian study, administration of folic acid and iron together with antimalarials to pregnant mothers resulted in increased maternal height as well as foetal growth, thus stressing the importance of nutritional care for the teenage mothers.