3.1 Characteristics of the study group
Description and comparison of the maternal and neonatal characteristics between SC-MCDA, SC-DCDA and ART-DCDA twins are displayed in Table S1 . Women in advanced maternal age accounted for 15.5% among SC-MCDA twins, 19.5% in SC-DCDA twins and 24.2% in ART-DCDA twins (p <0.001). Maternal prepregnancy body mass index showed significant differences only between SC-MCDA and ART-DCDA twins (p <0.05). In addition, the proportion of nulliparous women in ART-DCDA twins were higher than those in SC-MCDA twins (p <0.05). SC-MCDA twins had a shorter gestational age than SC-DCDA and ART-DCDA twins (p <0.05). Meanwhile, SC-MCDA twins were significantly lighter in birthweight and shorter in birth length than SC-DCDA and ART-DCDA twins (2468.82g vs 2643.62g and 2637.71g; 47.21cm vs 47.82 and 47.89cm; all p <0.05). The description of singleton and comparison with twins are displayed in Table S2 .