To investigate the influence of RA or preclinical RA on the risk of spontaneous abortion (SA) while taking age and duration of RA into consideration.
By linkage of data from Danish national registries, we established a nationwide cohort of pregnancies in Denmark from 1 January 1977 to 31 December 2014. We used multiple logistic regression to estimate; odds ratios (OR) for SA in women with RA or preclinical RA, compared with women without, and OR for SA by maternal age in women with RA or preclinical RA.
A total of 2 612 529 pregnancies were included. Women aged <35 years diagnosed with RA <5 years before pregnancy had an increased risk of SA (OR = 1.25 95% CI: 1.07, 1.48), compared with women without RA aged <35. Women at the same age diagnosed with RA ≥5 years before pregnancy had an OR of 1.14 (0.96-1.34), compared with women without. Among women with RA aged ≥35 years and women with preclinical RA at time of pregnancy, no increased risk of SA was found. The risk of SA increased by maternal age in both women with RA, preclinical RA and in women without.
Among women aged <35 years, the risk of SA was higher in women with RA compared with women without. After the age of 35 years, the risk of SA was no different from that among women without RA, even though the risk of SA increased with increasing age.