[Conditions of maternal work and low birth weight in Mexico City]

To study the association between maternal working conditions and low birth-weight in Mexico City.

Interviews of 2623 workers who gave birth in Mexico City hospitals during 1992 were analyzed. Information on the main biologic and social factors associated to low birth-weight was registered. Occupational stress was determined with the instrument designed by Karasek. Logistic regression models to evaluate the relationship between working conditions and low birth-weight were used, controlling by confounding variables.

Low birth-weight was more frequent in workers with working periods of more than 50 h/week (OR = 1.6; 95% CI = 1.17, 2.28) and with problems at work (OR = 1.5; 95% CI = 1.0, 2.25). Lack of tangible social support was identified as a risk factor for low birth-weight (OR = 1.7; 95% CI = 1.20, 2.33). Preventive working measures such as changes in tasks, shortening of working hours and leaves of absence due to illness did not show a beneficial effects on birth-weight, except for the maternity leave of absence. Mothers with no right to this had a 2.2 higher probability of giving birth to low weight children (95% CI = 1.66, 2.93).

These results emphasize the importance of identifying the occupational risk factors during pregnancy.