Mother's educational level and fetal growth: the genesis of health inequalities.

Background: Women of low socio-economic status (SES) give birth to lighter babies. It is unknown from which moment during pregnancy socio-economic differences in fetal weight can be observed, whether low SES equally affects different fetal-growth components, or what the effect of low SES is after taking into account mediating factors.

Methods: In 3545 pregnant women participating in the Generation R Study, we studied the association of maternal educational level (high, mid-high, mid-low and low) as a measure of SES with fetal weight, head circumference, abdominal circumference and femur length. We did this before and after adjusting for potential mediators, including maternal height, pre-pregnancy body mass index and smoking.

Results: In fetuses of low-educated women relative to those of high-educated women, fetal growth was slower, leading to a lower fetal weight that was observable from late pregnancy onwards. In these fetuses, growth of the head [-0.16 mm/week; 95% confidence interval (CI): -0.25 to -0.07; P = 0.0004], abdomen (-0.10 mm/week; 95% CI: -0.21 to 0.01; P = 0.08) and femur (-0.03 mm/week; 95% CI: -0.05 to -0.006; P = 0.01) were all slower; from mid-pregnancy onwards, head circumference was smaller, and from late pregnancy onwards, femur length was also smaller. The negative effect of low education was greatest for head circumference (difference in standard deviation score in late pregnancy: -0.26; 95% CI: -0.36 to -0.15; P < 0.0001). This effect persevered even after adjustment for the potential mediators (adjusted difference: -0.14; 95% CI: -0.25 to -0.03; P = 0.01).

Conclusions: Low maternal education is associated with a slower fetal growth and this effect appears stronger for growth of the head than for other body parts.