RESUMEN
Objective To study the mechanism of marcosomia by investigating insulin-like growth factor 2(IGF_2)imprinting status,expression level and the promoter usage in the placenta of macrosomia. Methods We selected heterozygous cases for Apa Ⅰ polymorphism in exon 9 of IGF_2 gene and then analyzed its imprinting status in 168 placentas of macrosomia and normal pregnancies.IGF_2 transcription levels and promoter usages in macrosomic and normal placenta were evaluated by using semi-quantitative RT- PCR assay.Results Thirty specimens of macrosomic placenta and 30 of normal placenta were identified as heterozygous for IGF_2.All of the heterozygous specimens showed maintenance of imprinting.The expression of placental IGF_2 mRNA(2.2?1.2)was significantly higher in macrosomia than that of normal weight group (1.6?0.6,P 0.05).Conclusion It is possible that over expression of IGF_2 in placenta contributes to macrosomia while the promoter usage and imprinting status are not associated with macrosomia.