We report the case of a 26 years old pregnant woman at 17 weeks amenorrhea, suffering from multiple sclerosis (MS) for 6 years, hospitalized for a relapse. Treatment of MS relapses is based on high dose corticosteroid infusions, A current infection would represent a contra-indication to this treatment. In our patient, C-reactive protein (CRP) levels were moderately increased (38 mg/L). This raised the question of the physiological CRP levels in pregnant woman. After reviewing the literature, we noticed that increased CRP levels may be found in normal pregnancy, however no consensual cut-off value is admitted up to date. Procalcitonin measurement may contribute to therapeutical decision, even if increased levels have also been reported during normal pregnancy.