Psychosocial predictors of low birthweight: a prospective study.

Objective: To examine the role of psychosocial risk factors for low birthweight.
Design: A prospective study.
Setting: Obstetric outpatient clinics of the University Hospital Vrije Universiteit, Amsterdam.
Participants: Three hundred and ninety-six nulliparous women.
Methods: Questionnaires on background variables, daily stressors, psychological and mental wellbeing, social support and work factors were completed by the women in the first, second and third trimester of pregnancy. Low birthweight for gestational age was defined at different cut off points: 1. < or = 10th customised birthweight centile (n = 69); 2. < or = 5th customised birthweight centile (n = 54); 3. < 3rd customised birthweight centile (n = 35); and 4. < or = the 10th Dutch birthweight centile (n = 40). Multivariate logistic regression was applied and the results were expressed in odds ratios and their 95% confidence intervals.
Results: When the cut off level was defined < or = 5th and < 3rd customised centile, the number of daily stressors in the first trimester was a statistically significant risk factor (OR 1.04, 95% CI 1.01-1.07 and OR 1.04, 95% CI 1.01-1.08). No significant psychosocial risk factors could be identified when low birthweight for gestational age was defined < or = the 10th customised birthweight centile. When low birthweight for gestational age was defined < or = the 10th Dutch birthweight centile, number of hours housekeeping per week in the first trimester (OR 1.59, 95% CI 1.03-2.46), low subjective severity rating of daily stressors in the first trimester (OR 0.41, 95% CI 0.17-0.97) and depressive mood in the first trimester (OR 1.12, 95% CI 1.01-1.24) were statistically significant psychosocial risk factors after controlling for maternal weight and height, number of cigarettes smoked per day and educational level.
Conclusions: In the first trimester of pregnancy maternal psychosocial factors are associated with an increased risk of low birthweight. The specific psychosocial risk factors found were different when the definition of low birthweight was changed. Therefore, in this field of research, we suggest use of the most valid outcome measure for low birthweight, being the customised birthweight centiles.