To evaluate the normal range of inter-recti distance (IRD) 42-60 days postpartum, and then make the preliminary decision when the treatment for postnatal diastasis recti abdominis should be given.

A total of 126 women at 42-60 days postpartum were continuously collected to perform transabdominal sonography from August 2019 to August 2020 at the Affiliated Suzhou Hospital of Nanjing Medical University. IRD measurements were made at the upper margin of the umbilicus, 3 cm above the umbilicus, 5 cm above the umbilicus, and 3 cm below the umbilicus in the supine, flexion, and standing positions. Two independent sample rank-sum tests were used to compare differences in rectus ventral spacing at different umbilical levels between the transvaginal delivery and cesarean delivery and between first and non-first birth groups. The 20th and 80th percentiles were used to define the reference range of postpartum IRD.

The differences of IRDs between the vaginal delivery group (n=89) and the cesarean section group (n=89) were statistically significant (P＜0.05), but there were no significant differences in IRDs between the first (n=72) and non-first birth groups (n=54) (P＞0.05). The postpartum IRDs had a skewed distribution in the vaginal delivery group, with a percentile interval of 20%-80%; the IRDs at the four measurement points (3 cm above the umbilicus, 3 cm above the umbilicus, 5 cm above the umbilicus, and 3 cm below the umbilicus) in different positions were as follows: supine position (mm): 19.60-38.30, 15.10-28.80, 11.00-21.50, and 2.70-15.50; flexion position (mm):16.70-30.90, 12.90-26.30, 9.20-19.90, and 1.90-12.00; standing position (mm): 19.00-39.10, 15.90-35.50, 11.20-28.50, and 0.00-8.60, respectively. In the cesarean section group, there was a percentile interval of 20%-80%, and the IRDs at the four measurement points in different positions were: supine position (mm): 25.92-44.04, 19.78-32.44, 14.94-28.76, and 7.78-24.88; flexion position (mm): 20.12-36.68, 17.20-28.44, 13.38-26.24, and 4.08-18.62; standing position (mm): 28.80-45.68, 21.18-40.38, 18.04-33.70, and 0.00-18.62, respectively.

As the inner edge of the rectus abdominis is the easiest to be distinguished in the flexion position, it is suggested that the maximum space between the rectus abdominis in flexion position be more than 30.90 mm (vaginal delivery) and 36.68 mm (caesarean delivery), and when the measured value exceeds the postpartum IRD of 80% women, a treatment is suggested.