Objective:To investigate the multi-sites high frequency ultrasound features of rectus diastasis (RD) in early postpartum women and their relationships with different delivery modes.Methods:Total of 571 primiparas who gave birth in the Obstetrics and Gynecology Hospital Affiliated to Zhejiang University Medical College from March to May 2020 and underwent 6-week postpartum examination were chosen, they were divided into vaginal delivery group (336 cases) and the cesarean section group (235 cases). The inter-rectus distance(IRD) of five loci (umbilical on 4.5 cm, umbilical on 3 cm, umbilical edge, edge of umbilical, umbilical down 3 cm) at resting state and two loci (umbilical edge, edge of umbilical) at curling state as well as the rectus thickness on the right side of umbilical level were observed by high frequency ultrasound. The impacts of the two delivery modes on IRD at each site and the changes of IRD under the two conditions were analyzed. Spearman correlation analysis was used to evaluate the correlation between the thickness of rectus abdominis and IRD at each site.Results:The incidence of early postpartum RD was 79.7% (455/571), most of which occurring at 3 cm above the umbilicus and the umbilicus levels. At resting state, the IRDs at the 5 loci of vaginal delivery group were (1.62±0.79)cm, (2.03±0.84)cm, (2.65±0.94)cm, (2.09±0.93)cm, and 0.54(0.00, 1.13)cm respectively, while the IRDs at 5 loci of the cesarean section group were (1.75±0.85)cm, (2.26±0.99)cm, (2.99±1.14)cm, (2.57±1.21)cm, and 1.00(0.41, 1.59)cm, with statistical differences at all the levels between groups ( P<0.05). Under the curling state, the IRDs at the 2 loci of vaginal delivery group were (2.10±0.84)cm and (1.66±0.86)cm respectively, while the IRDs at the 2 loci of cesarean section group were (2.28±0.87)cm and (1.91±0.87)cm, with statistical differences between groups( P<0.05). The incidences of increased IRD when compared between resting and curling states at the upper and lower umbilicus in the vaginal delivery group were 16.1% and 26.5%, with 17.4% and 20.4% in the cesarean section group. At the resting state, there was a significant difference in the thickness of rectus abdominis between the vaginal delivery and cesarean section groups [(0.74±0.12)cm vs (0.67±0.12)cm, P<0.05]. At the curling state, the difference between two groups was statistically significant [(1.11±0.23)cm vs (0.99±0.22)cm, P<0.05]. The thickness of rectus abdominis was negatively correlated with IRD(all the 5 loci at resting state, rs=-0.116, -0.140, -0.185, -0.143, -0.144, all P<0.01; and the upper umbilical loci at curling state, rs=-0.091, P<0.05). There was no significant correlation between the thickness of rectus abdominis and IRD at the lower umbilical edge at the curling state ( P>0.05). Conclusions:High frequency ultrasound can evaluate the morphological characteristics of the abdominal rectus muscle in early postpartum stage. Compared with vaginal delivery, rectus abdominis thickness, the IRD is larger in cesarean section primiparas, but less affected by the curling state.