Imprinting and Promoter Usage of Insulin-Like Growth Factor II in Twin Discordant Placenta.

Case reports from infant twins suggest that abnormal genomic imprinting may be one of the important causes of twin discordance, but it is unknown whether abnormal genomic imprinting occurs in the placenta. Therefore, we sought to determine the relationship between the imprinting of insulin-like growth factor II (IGF-II) in placenta and twin discordance. We analyzed the imprinting and promoter usage of IGF-II in placenta of normal twins (T0 group), weight discordance (T1 group), and phenotype discordance (T2 group). We found the incidence of loss of imprinting (LOI) for IGF-II was higher in the T2 group than that in the T0 and T1 groups, while there was no difference between T0 and T1 groups. The transcripts of promoter 3 were lower in the T2 group than in the T0 and T1 groups, and lower in the twin placenta with LOI than in those with normal imprinting. Our findings indicate that the promoter 3 specific LOI of the IGF-II gene may be closely related with phenotype discordance, not weight discordance.

[Characteristics of IGF-II gene imprinting in twin placentas].

OBJECTIVE: To compare insulin-like growth factor II (IGF-II) gene imprinting in twin placentas with singleton ones and to determine whether imprinting was influenced by assisted reproductive technology, zygosity and fetal sex. METHODS: One hundred and sixty cases of twin placentas and 42 cases of singleton ones were recruited. Allele-specific IGF-II expression was determined by reverse transcription-PCR combined with analysis of an Apa I-sensitive restriction fragment length polymorphism. RESULTS: Although the incidence of IGF-II imprinting loss was higher in normal twin placentas than in singleton ones (20.6% vs 8.7%), there was no statistical significance. There were no significant differences between twins conceived by assisted reproductive technology and those conceived spontaneously (17.9% vs 24.4%), and between dizygotic and monozygotic twins (22.4% vs 16.7%). The incidence of IGF-II imprinting loss in placenta of female twins was statistically higher than that of male ones (26.4% vs 9.8%). CONCLUSION: The risk of IGF-II gene imprinting loss is higher in female twins and has no relationship with assisted reproductive technology and zygosity.

[Perinatal outcome of discordant twin pregnancies].

OBJECTIVE: To discuss peripartum obstetrics events and perinatal outcomes of discordant twin pregnancies. METHODS: Discordant growth was defined as the intrapair difference in birth weight more than 20%. Ninety-six discordant twin pregnancies (observed group) and 349 concordant ones (control group) were compared in pregnant complications and perinatal outcomes. RESULTS: No difference of maternal age, chorionicity, methods of conception and fetal gender were found between two groups. Observed group had a higher incidence of late abortion (13.5% vs 4.3%, P < 0.05), polyhydramnios (22.9% vs 10.0%, P < 0.01), twin-twin transfusion syndrome (9.4% vs 1.4%, P < 0.01), placental abruption (5.2% vs 1.1%, P < 0.05), perinatal death (22.9% vs 4.4%, P < 0.01) and of fetal malformation (5.2% vs 1.3%, P < 0.01) than control group. In observed group, perinatal death was higher in smaller twin than in larger one (30.2% vs 15.6%, P < 0.05). The incidences of perinatal death were 4.4%, 11.0% and 41.9% and fetal malformation were 1.3%, 5.1% and 5.4% when the discordance was < or = 20%, 20%-30%, and > or = 30%, respectively (P < 0.05). CONCLUSIONS: Discordance places twins at increased risk for late abortion, premature delivery, polyhydramnios, twin-twin transfusion syndrome, placental abruption, perinatal death and fetal malformation. The smaller twin and great discordance are risk factors for poor outcomes. Chorionicity, methods of conception and fetal gender are not responsible for discordant growth.