To investigate the association of pregnancy status with age at progressive multiple sclerosis (MS) onset.

Female sex is the most important risk factor for MS. However association of  pregnancy status with evolution of progressive MS has not been sufficiently investigated.

A progressive MS clinical series (n=202, 134 women, 68 men) was studied. Pregnancy (parity/para: number of pregnancies reaching viable gestational age) and age at progressive MS onset and relapsing-remitting MS (RRMS) onset were evaluated.

Nulliparous women (n=32) had earlier progressive MS (PMS) onset (41.4±12.6 yrs) than women with ≥1 parity (n=95; 47.1±9.7 yrs) (p=0.012). PMS onset age also increased by parity with a dose-effect trend (para 0: 41.4±12.6 yrs, para 1-3: 46.4±9.2 yrs, para ≥4: 52.6±12.9 yrs) (p=0.002). In the secondary progressive MS (SPMS) only subgroup, nulliparous women had earlier age at SPMS onset (n=19; 41.5±9.2 yrs) than women with ≥1 parity (n=57; 47.3±10.6 yrs) (p=0.049). RRMS onset age was also earlier in the same nulliparous group (27.5±7.0 yrs) than in women with ≥1 parity (33.0±9.4 yrs) (p=0.021). Dose effect trends were again observed by parity for age at SPMS onset (para 0: 41.5±9.2 yrs, para 1-3: 46.2±9.9 yrs, para ≥4: 52.6±12.9 yrs) (p=0.010) and age at RRMS onset (para 0: 27.5±7.0 yrs, para 1-3: 32.4±9.3 yrs, para ≥4: 35.8±9.8 yrs) (p=0.012).

Nulliparity seems to be associated with earlier evolution to progressive MS. There is further need for a larger study to understand whether pregnancy related factors lead to earlier development of progressive MS, or whether MS-associated factors lead to nulliparity either by choice or due to biological reasons.