Objective: To test the stress hypothesis that women who give birth to small for gestational age infants lack important psychosocial coping resources, such as a sufficient social network, social support and control in daily life.
Design: A prospective cohort study of nulliparous pregnant women.
Setting: Antenatal care units in the city of Malmö, Sweden.
Population: All women (n = 994) during a one year period (1991-1992) were invited, and 872 (87 x 7%) participated. This study was restricted to pregnancies resulting in singleton live birth (n = 826); 6 x 7% of infants were classified as small for their gestational age.
Methods: Self-administered questionnaires were given to all women at the time of their first antenatal visit.
Main outcome measures: The classification of small for gestational age was based on a gender-specific intrauterine growth reference curve. Newborn babies were classified as being small for gestational age if their birthweight was > 2 SD below the mean weight for gestational age.
Results: Lack of psychosocial resources, such as social stability, social participation, emotional and instrumental support, all increased the likelihood of delivering an infant that was small for gestational age. The odds ratios when controlled for demographic background factors, lifestyle factors and anthropomorphic measures were: OR 1 x 7 (95% CI 0 x 9-3 x 3) for women with poor social stability; OR 2 x 2 (95% CI 1 x 1-4 x 4) for women with poor social participation; OR 2 x 6 (95% CI 1 x 2-5 x 7) for women with poor instrumental support; and OR 1 x 5 (95% CI 0 x 8-2 x 8) for women with poor emotional support. Simultaneous exposure to a poor total network index, as well as a poor total support index showed a significantly increased odds ratio for having a small for gestational age baby: OR 3 x 3 (95% CI 1 x 6-6 x 7) and OR 2 x 7 (95% CI 1 x 3-5 x 6), respectively. A synergy index of 9 x 0 and 6 x 8 supported the assumption of an interaction between immigrant status and poor total network or poor total support, in a synergistic direction.
Conclusions: The findings support the stress-hypothesis that a lack of psychosocial resources might increase the risk of giving birth to a baby that is small for gestational age.