Intrauterine hypoxia -- a phenomenon peculiar to the second twin.

During a 5-year period twin births occurring at the university hospital were investigated for the presence of clinical and biochemical symptoms of intrauterine hypoxia. It appears that intrauterine hypoxia, when detectable, is limited to the second twin. Some factors which may influence the oxygenation of the second twin have been analysed, i.e., the mode of delivery, the time interval between deliveries, and the duration of gestation. No single explanation for the genesis of the hypoxia seems to be valid.