Women with inflammatory polyarthritis have babies of lower birth weight

To assess the effect on fetal outcome, and development of the child over the first 8 months of life, of rheumatoid arthritis (RA) during pregnancy.

Women with RA or undifferentiated inflammatory polyarthritis (IP) were recruited from throughout the UK and followed prospectively from late pregnancy to 8 months postpartum. Matched controls were obtained from general practitioners. The babies' health at birth and development at 8 months were monitored by the weight, head circumference, and length. Potential confounding variables were noted.

One hundred thirty-three women with RA or undifferentiated IP took part in the study. There were 5 (4%) admissions for hypertension during pregnancy and no cases of preeclampsia. Cesarean section was common (23%). Matched controls were found for 103 (77%) subjects. There were no significant differences between groups in head circumference or length at birth. Babies born to women with arthritis had lower mean birth weight than controls [3.3 kg (standard deviation 0.5) compared to 3.5 kg (0.4); p = 0.004], even after adjustment for potential confounding factors. Within the patient group those whose arthritis was in remission had significantly heavier babies than those with active disease [mean 3.5 kg (0.5) compared with 3.3 kg (0.5); p = 0.04]. This trend was still apparent at 8 months, but differences were no longer statistically significant.

This is the first relatively large prospective study of the effects on mother and baby of RA during pregnancy. The results suggest that, although disease improves in most women during pregnancy, it is still sufficiently active to have a modest negative effect on birth weight.