Data Safety and Monitory Board interim review (March 17, 1999) The DSMB reported that the transmission rate in the longest arm (long treatment of both mother and baby), was significantly lower than that in the shortest arm (short treatment of both the mother and the baby) and this discrepancy was larger than the previously agreed on difference which, if found, would call for changing the study design. In addition, the transmission rates in the remaining two arms of the study were similar to that in the longest arm. The difference that was found could not be explained by any baseline characteristics of the participants, such as maternal age, gestational age at delivery, birth weight, cesarean section rate, or any others.