In this project we developed a social support and health education intervention meant to answer whether or not a program of this kind, within the present medical system, can improve perinatal outcomes. A multicenter randomized controlled trial was conducted in four Latin American countries. In Mexico, the project was carried out in a third level obstetric hospital. Patients were screened between the 15th and 22nd week of gestation. Inclusion criteria were factors associated with high risk of low birthweight. A total of 620 women were recruited, randomized and followed up during pregnancy and up to the 40th day post partum. Women in the intervention group were visited four to six times during pregnancy, could use a telephone hot line and a consultation service. A poster and a pamphlet meant to reinforce health education were handed out in the first visit. A "guided tour" for women at the end of pregnancy was organized periodically. Outcomes were measured in both groups at the 36th week of gestation, post partum and 40 days after delivery. Neonatal outcomes were obtained by blind interviewers from the clinical records. Neither in the multicenter nor in the Mexican sample were we able to modify the incidence of low birthweight and prematurity. However, in Mexico we obtained positive effects on birthweight and gestational age in the whole sample and in some specific strata. These results strongly suggest the convenience of replicating the study in Mexico.