There is conflicting evidence regarding the effect of depression during pregnancy on birth weight. We used data from the Avon Longitudinal Study of Parents and Children to investigate whether depressive symptoms during pregnancy in 10 967 women led to low birth weight at term in their offspring.

Those with a high depressive symptom score during pregnancy were more likely to have babies of low birth weight (95% CI 1.16-2.40, P<0.01), but this attenuated after adjustment for confounders (OR=1.29,95% CI 0.87-1.91, P=0.210). Hence there is little evidence of an independent association between depressive symptoms during pregnancy and birth weight.

Low birth weight at term is a marker of intrauterine growth restriction and can result from prenatal exposure to high maternal levels of steroids (Gur et al, 2004). As maternal stress results in raised cortisol, psychological symptoms during pregnancy may cause intrauterine growth restriction. Depression and anxiety are common during pregnancy, but evidence for any effect on intrauterine growth is conflicting (e.g. Kelly et al, 2002; Andersson et al, 2004). In this large prospective study we investigated whether mothers with symptoms of depression and anxiety during the second trimester of pregnancy are at greater risk of having babies of low birth weight at term.

Method
We used data collected as part of the Avon Longitudinal Study of Parents and Children (ALSPAC; http://www.alspac.bris.ac.uk). In total, 14 541 women were enrolled and 13 194 (90.7%) completed a questionnaire at 18 weeks’ gestation.

Questionnaires included the Edinburgh Postnatal Depression Scale (EPDS; Cox et al, 1987) and sub-scales of the Crown-Crisp Experiential Index (CCEI), which measures `free-floating’ anxiety (Crisp et al, 1978) which were completed at 18 and 32 weeks of pregnancy. The EPDS has been validated for use during pregnancy and at other times (Murray & Cox, 1990; Shakespeare, 2001). The CCEI correlates well with other measures of anxiety in women during pregnancy and the internal consistency exceeds 0.8.

Birth weight was obtained directly by research staff. We included only those babies delivered between 37 and 43 weeks’ inclusive and we excluded multiple births as these babies are more likely to be of lower birth weight.

Data on confounding factors came from the self-report postal questionnaires and included gender of the baby, gestational age, smoking, maternal age, parity, educational level, alcohol and caffeine use during pregnancy, chronic disease, pre-pregnancy body mass index, ethnicity and a history of miscarriage, Caesarean section, prior low birth weight, or preterm births.

We used linear and logistic regression analyses with birth weight as a continuous outcome or dichotomised as low birth weight (

<2500 g) at term. We used the multiple imputation by chained equation method to impute missing data for confounders (van Buuren et al, 1999).

RESULTS
Analyses were performed on 10 967 women, of whom 1519 (13.9%, 95% CI 13.2-14.5%) scored >12 on the EPDS at 18 weeks of pregnancy, indicating a likely diagnosis of depression. There were 8427 (76.8%) women with complete data on all confounding variables. We imputed missing data on confounders in all adjusted analyses.

Women scoring >12 on the EPDS at 18 weeks of pregnancy had babies that were 33.8 g lighter (95% CI 8.0-59.7, P=0.01) compared with women with an EPDS score

<13. Following adjustment for confounders, an EPDS score >

12 was no longer significantly associated with birth weight: babies born to mothers with probable depression were 1.1 g lighter (95% CI -22.1 to 24.3, P=0.4). The strongest confounder appeared to be smoking. The coefficient following adjustment for gender, maternal age and gestation was -25.9 (95% CI -49.9 to -2.02), this dropped to -1.0 (95% CI -24.9 to 22.9) following additional adjustment for smoking. Using anxiety as the exposure variable we found similar results (details available from the authors).

Following adjustment, there was no effect restricted to those with higher symptom scores; mothers scoring >=16 on the EPDS at 18 weeks of pregnancy had babies that were 22.5 g lighter (95% CI -12.5 to 57.4, P=0.207) than those scoring <13.

We repeated these analyses with the outcome categorised into low birth weight at term according to the traditional definition of <2500 g) (Fig. 1). The drop in the estimated odds ratio was greatest following adjustment for smoking. The odds ratio following adjustment for gender, gestation and maternal age was 1.57 (95% CI 1.08-2.29), dropping to 1.38 (95% CI 0.94-2.01) after adjustment for smoking.

With anxiety as the exposure variable we found very similar results to those seen for depression (details available from the authors). We found a weak association with prolonged exposure to depressive symptoms. Those scoring >12 on the EPDS at both 18 and 32 weeks of pregnancy had babies that were 40.2 g lighter (95% CI 3.8-76.6, P<0.05) than those with an EPDS score <13 at both times. This association diminished and was no longer statistically significant following adjustment.

The British Journal of Psychiatry (2007) 191: 84-85. doi: 10.1192/bjp.bp.105.016568
Jonathan Evans, MRCPsych, MD
Academic Unit of Psychiatry, University of Bristol

Jon Heron, PhD
Avon Longitudinal Study of Parents and Children, Department of Community Based Medicine, University of Bristol

Roshni R. Patel, MRCOG, PhD
Division of Obstetrics and Gynaecology, University of Bristol

Nicola Wiles, PhD
Academic Unit of Psychiatry, University of Bristol, UK

Correspondence: Dr Jonathan Evans, Academic Unit of Psychiatry, University of Bristol, Cotham House, Cotham Hill, Bristol BS6 6JL, UK. Email: .(JavaScript must be enabled to view this email address)

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