Preterm birth increases the child's risk of cerebral palsy. Observational studies as well as randomized studies find that magnesium sulphate given to women in preterm birth decreases such risk. A Cochrane meta-analysis of the randomized studies shows no change in mortality, whereas some observational studies find a mortality decrease. It is important to identify the neuroprotective mechanism and to decide whether these results are relevant in the current Danish obstetrical practice. Should we use magnesium sulphate now or should questions about doses, time of administration and maternal side effects be answered first?