Twin pregnancies are regarded as high risk pregnancies. It results from the possibility of occurrence of numerous complications both like the ones in singleton pregnancies and those characteristic for multiple pregnancy only. The complication occurring exclusively in multiple pregnancies is discordant intrauterine growth of the fetuses.

The aim of this study was a response to the question if there a relationship between the type of afterbirth and twin birth weight discordance.

Material and methods: Material of the research consisted of 186 afterbirths derived from successful twin pregnancies. In the study the following were taken into consideration: evaluation of placenta/placentas types (mono- or dichorionic), place of umbilical cords insertion, and differences concerning birth weight of newborns.

Results: The birth weight discordance of less than 10% (Io) in the twins was noted in 52.7% of pregnancies (n = 98), discordance of 10-20% (IIo) was observed in 30.1% (n=56), and over 20% (IIIo) in 17.2% (n=32). The birth weight discordance of the third degree was observed significantly more often in dichorionic diamniotic pregnancies with fused placentas. The discordance of third degree (>20%) occurred in 38.2% of female-male pairs, in 35.7% of female-female ones and in 24.3% of male-male pairs. In case of coexistence of both normal umbilical cord insertions the birth weight discordance of third degree occurred in 17.8% of pregnancies, in case of co-occurrence of the abnormal insertion with the normal one – in 21,8% of cases, and in case of the two abnormal insertions – in 10.5%. No statistically significant differences were found.

Conclusions: There is a relationship between the type of afterbirth and birth weight in twins. The largest birth weight discordance between fetuses occurs in the following cases: in dichorionic pregnancies with fused placental discs, in case of co-existence of abnormal and normal umbilical cord insertions and in female-male pair of twins.