[Perinatal factors which affect low birth weight].

The incidence of low-birth weight babies in the Santo Tomás maternity ward was 9% between the first of August of 1992 and the 31 of July of 1993. We found a higher risk of having low birth weight babies if the mother was toxemic, without prenatal care of low socioeconomic status and if she was single. We did not find an association with adolescence, short mother's height, low educational status and primi- or multiparity of 5 or more.