Women whose psychosocial resources are inadequate to help them cope with the stresses of a first birth may have an elevated risk of bearing an infant who is small for gestational age, according to results of a Swedish prospective cohort study.1 Among a sample of women who had a first birth in the early 1990s, those who participated little in social activities and those who had limited access to advice and information were 2-3 times as likely as women with greater psychosocial resources to have an underweight infant.

The sample consisted of women obtaining prenatal care at four clinics in Malmö in 1991-1992. Participants answered a questionnaire that covered their background and lifestyle characteristics, as well as seven psychosocial factors: social stability (the degree of a woman's involvement in formal and informal groups), social participation (the extent to which she participates in social groups), emotional support (the support she receives from others), instrumental support (her access to advice, information and services), support from the child's father and from her mother, and conditions at her workplace. Information pertaining to the pregnancy and its outcome was obtained from women's medical records and a perinatal database.

A total of 826 women who had a singleton live birth were included in the analyses. Most were in their 20s (70%), had been born in Sweden (78%), were living with a partner or spouse (88%), and had had 12 or fewer years of schooling (61%). Thirty percent smoked; 18% smoked at least 10 cigarettes daily.

On average, the infants weighed 3,394 g at birth and were delivered at 39 weeks' gestation. Seven percent of infants were small for gestational age--that is, their birth weight was at least two standard deviations below the mean for their gender and gestation. The majority of these infants (80%) were born at term, and nearly half (47%) weighed less than 2,500 g.

In univariate analyses, the odds of giving birth to a baby who was small for gestational age were approximately doubled among women who were short (157 cm or less), those who were not Swedish-born and those who smoked 10-19 cigarettes a day. Low levels of social stability, social participation and emotional support also were associated with a roughly doubling of the odds of this outcome; the effect of a low level of instrumental support was similar but reached only a borderline level of statistical significance.

To assess the independent contributions of the psychosocial factors that had significant (or nearly significant) effects at the univariate level, the investigators conducted a series of multiple logistic regression analyses, controlling for factors that are associated with both the psychosocial variables and the risk of bearing an underweight infant. They first controlled for the mother's age, height and weight, then added her native country (Sweden vs. other) and educational level; next, they controlled for all of these factors plus the mother's alcohol consumption, smoking and level of physical exercise.

According to these analyses, social stability and emotional support do not have significant independent effects on the risk of bearing an underweight infant. However, women with a low level of social participation had an elevated risk in each set of calculations (odds ratios, 1.9-2.2). And the effect of low instrumental support grew as the researchers included more controls: The odds ratio was 1.9 and marginally significant in the initial analysis, but increased to 2.6 and achieved statistical significance when all factors were taken into account.

Fourteen percent of the study participants experienced some type of medical complication during pregnancy (e.g., urinary tract infection, bleeding or preterm contractions), and these women were marginally more likely than others to have an infant who was small for gestational age. However, a set of multivariate analyses that controlled for the effects of those medical risk factors revealed that their inclusion did not alter the results involving the psychosocial variables.

The analysis further showed the additive effects of inadequate psychosocial resources. Women who had low levels of both social stability and social participation were about three times as likely as those with neither of these factors to have an underweight infant (odds ratio, 3.3). Similarly, those who simultaneously registered low instrumental and emotional support had nearly triple the risk of this outcome (2.7).

While the researchers conclude that psychosocial factors appear to influence fetal growth, they note that the mechanism underlying the association is unclear. The effects may be indirect, operating through unhealthy behavior, such as smoking or drinking. Or they may be direct: Stress hormones may decrease the blood flow to the uterus or alter the immune system, causing adverse effects. Another possibility is that an increased secretion of certain hormones in response to stress may affect the mother's weight gain and thus the infant's birth weight. Whatever the reason for the relationship, the investigators contend that "pregnant women with insufficient psychosocial resources are a high risk group that should be identified early in pregnancy and offered specific intervention programmes with individualised support."--D. Hollander


1. Dejin-Karlsson E et al., Association of a lack of psychosocial resources and the risk of giving birth to small for gestational age infants: a stress hypothesis, British Journal of Obstetrics and Gynaecology, 2000, 107(1):89-100.