Background The influence of pregnancy on Multiple Sclerosis (MS) has been extensively studied but such influence on Latin American women with MS has not been characterized. Our objective was to describe the course of pregnancy and birth outcome in Argentinean MS patients and the evolution of MS during pregnancy and after delivery. Method We used a retrospective design in eight MS centers in Argentina and administered a survey to women with definite MS (Mc Donald) with pregnancies during or after MS onset. We contacted 355 women of which 81 met inclusion criteria. We recorded 141 pregnancies. Results Involuntary abortion was observed in 16% of pregnancies (95% CI = 10–23). Thirty five women received immunomodulatory therapy (IMT) before 42 pregnancies. Twenty three (55%) out of 42 pregnancies were exposed to IMT. The mean time of IMT discontinuation before conception in 19 (45.2%) pregnancies without exposure, was 104 days (95% CI = 61.0–147.0). There were 103 deliveries: 79% full term. Birth defects were detected in 19% of pregnancies exposed to IMT (95% CI = 4–46) and in 2% of non-exposed (95% CI = 0.3–8.0). The mean relapse rate was: pre-pregnancy year: 0.22 (95% CI = 0.12–0.32); pregnancy: 0.31 in 1st (95% CI = 0.10–0.52), 0.19 (95% CI = 0.03–0.36) in 2nd, and 0.04 in 3rd trimester (95% CI = –0.04–0.12); 1st trimester post delivery: 0.82 (95% CI = 0.42–1.22). Conclusion We observed a higher rate of birth defects among infants exposed to immunomodulators in utero than those not exposed. The reduction in MS relapses during 2nd and 3rd trimester of pregnancy and its increase during postpartum is consistent with previous reports.