Cited studies did not show relation between maternal anxiety and birth weight

Editor—Teixeira et al¹ state that “some studies have shown that babies of stressed or anxious mothers have a significantly lower than average birth weight for gestational age and tend to be born early” and then reference four papers, one of which is mine.² The St George's birthweight study was a large prospective study of pregnant women which measured anxiety and depression throughout pregnancy. We found no association between anxiety and depression and either prematurity² or low birth weight.³ Nor was any association found with life events as measured by Paykel's interview for recent life events.

Interestingly, having demonstrated that high anxiety levels are linked to an increased uterine artery resistance index, Teixeira et al note that the index is predictive of intrauterine growth retardation. Thus it is paradoxical that one of the largest cohort studies of anxiety, depression, and stress in pregnancy, which was also referenced, found no association between any of the above and intrauterine growth retardation.⁴ Although the results were based on a single psychosocial assessment at 26 weeks, like the St George's study, it found no relation between anxiety and depression and prematurity or low birth weight. There was, however, an association between increasing levels of stress and prematurity and low birth weight.

Finally, the Danish study of 5873 women that was cited found that women who had one or more life events that they perceived as being highly stressful had a risk of preterm delivery 1.76 times greater than those without stressful life events.⁵ This sounds impressive but equates to a decrease in length of gestation of 1.06 days, which is of no clinical importance.

The findings of Teixeira et al are interesting and warrant further study. However, caution has to be exercised in interpreting large epidemiological studies that confine psychological assessments of pregnant women to the beginning of the last trimester. Women at this stage may already be aware, through ultrasound assessments, fundal measurements,or blood pressure problems, that there is a problem with their pregnancy, which may induce stress and anxiety.