The combination of weight discordance and prematurity implies a high perinatal morbidity and mortality for the affected twins. Several pathomechanisms may be responsible for the weight difference in twins including a different genetic growth potential in dizygotic twins, placenta insufficiency in one twin, and chronic feto-fetal transfusion (CFFT). Little is known about neonatal morbidity and mortality of discordant twins. Therefore, a retrospective, case-controlled study on preterm discordant twins up to 34 weeks gestation was carried out. Twenty-seven (27,3%) of 99 twin pairs born in our clinic had a birth weight difference of more than 20%. The control group consisted of 27 non-discordant twins matched for gestational age. Discordant twins showed a significantly higher mortality (19%) than the control twins (2%). Severe intracranial haemorrhage (ICH) and persistent ductus arteriosus Botalli (PDA) were found more often in discordant twins than in the control group. The increased mortality and morbidity of discordant twins compared with concordant twins matched for gestational age indicates that the increased morbidity and mortality of preterm weight discordant twins is not only due to prematurity, but is also related to the discordance itself. Thirteen (48.1%) of the weight discordant twin pairs fulfilled the criteria for CFFT. Twins with CFFT differed significantly from controls with respect to the incidence of mortality and the rate of severe ICH, PDA, and the necessity of postnatal cardiopulmonary resuscitation. By contrast, no significant differences were found between discordant twins without CFFT and controls. Thus, CFFT appears to be a major contributing factor for increased mortality and morbidity of weight discordant twins. Intra-twin pair analysis revealed a higher rate of postnatal hypoglycaemia in the smaller twins only, probably caused by insufficient glycogen storage due to intra-uterine malnutrition. Mortality was the same for both the larger and the smaller twins. It may be concluded that neonatal outcome of smaller twins who have survived intra-uterine malnutrition is the same as in larger twins. Intra-twin pair analysis in twins with CFFT revealed no significant differences except for a higher rate of ICH grade 2-4 in the larger twins which might be explained by hypervolaemia of the recipient.
Conclusion: Morbidity and mortality of weight discordant twins are increased. CFFT appears to be a major contributing factor for the increased mortality and morbidity. Postnatal mortality was the same in acceptor and donor; however, the acceptor had a higher postnatal morbidity.