Women with multiple sclerosis (MS) want to enjoy life to the full, including giving birth to and raising children. MS, in itself, has little impact on the course of pregnancy. It is well established that disease activity is considerably reduced during the last two trimesters of pregnancy. 1 Breast-feeding has a neutral effect on MS course. We have reported that pregnancy may hasten transition to secondary progression. 2 Family planning for a woman with MS must consider the following: a 3-5% risk of MS transmission to the child, treatment cessation, a post-partum relapse rate of around 30%, resumption of disease-modifying therapies (DMT), and the possibility of a lessened capacity to take care of the child. The only demonstrated effects of standard DMTs on pregnancy outcomes are a slightly decreased child birth weight and length, and an increased rate of spontaneous abortions with interferons. 3 Uncertainty remains over some possible long-term effects of treatments on the child. Women are generally unwilling to take any DMT during pregnancy, so that treatment is almost always deferred. DMT interruption carries the risk of disease reactivation, so that it is now advised to continue DMTs until a pregnancy test is positive. There is still, though, a high percentage of unplanned pregnancies. Natalizumab (NZB) is highly effective in reducing clinical and magnetic resonance imaging (MRI) manifestations of MS. Its use as a 4-weekly IV infusion is convenient, and is well tolerated in the short term. Alpha4-integrin, which is the target of NZB, plays an active role in fertilization, implantation, placental and cardiac development. When antagonized with NZB in pregnant animals, severe birth defects have been reported. Risks associated with NZB exposures during pregnancy and potential adverse effects on the developing fetus have therefore been expected.There are some reports of NZB exposure during pregnancy. In the manufacturer's (Biogen-Idec) registry on 364 pregnancies on NZB, mostly after very short and early exposure, 30 children (8%) had birth defects, mostly mild. The rate of major defects rate was the same as in the general population and there was no increased abortion rate. In this issue, Ebrahimi et al. 4 report on 101 women who were exposed to NZB around conception time and who experienced 102 deliveries. They had received an average of 18 NZB infusions before becoming pregnant. Only one of these women was exposed during the third trimester of pregnancy. The others 100 were exposed shortly before conception, or during the first few weeks of pregnancy. Ebrahimi et al.'s data uncover a higher miscarriage rate and lower birth weights in NZBtreated women, when compared with healthy controls. Amongst the non-live births, three fetuses had genetic anomalies. Rates of major malformations, low birth weight, and premature birth were not different from those found in the general population. Twentyone women experienced a relapse during pregnancy that required at least one course of steroid treatment. There is no mention of ...