To quantitatively evaluate diastasis recti abdominis in postpartum women by high frequency ultrasound, investigate the appropriate diagnostic threshold, and identify the factors related to diastasis recti abdominis.

From April to July 2019, 51 women at 6-30 months after delivery at Third Hospital of Peking University were recruited. Age, height, weight, body mass index, postpartum time, mode of delivery, and delivery times were collected. Abdominal circumference was measured. Subcutaneous fat thickness and maximum rectus abdominis distance during relaxation and contraction were evaluated by ultrasound. Pearson correlation analysis was used to explore the relationship between rectus abdominis distance and age, postpartum time, height, and physique. Point biserial correlation analysis was used to explore the correlation between delivery mode or delivery times and rectus abdominis distance. Independent sample t test was used to compare the difference of rectus distance in relaxation or contraction state between cesarean section and natural delivery women.

The average maximum distance of the rectus abdominis was (2.88±1.04) cm in relaxation and (2.45±1.15) cm in contraction. When 75% of the rectus abdominis distance deviated from the normal population was set as the diagnostic cut-off value, the diagnostic cut-off values of diastasis recti abdominis during relaxation and contraction were 3.0 cm and 2.8 cm, respectively. There was a linear correlation between rectus abdominis distance during relaxation and contraction (r=0.899, P＜0.001). There was no significant correlation between the distance of the rectus abdominis and age, height, weight, body mass index, postpartum time, abdominal circumference, subcutaneous fat thickness, or delivery times. Only the mode of delivery had a weak correlation with the distance of the rectus abdominis during contraction (r=0.369, P=0.008). There was no significant difference in the distance of the rectus abdominis between the first and second births. The distance of the rectus abdominis in women with a caesarean section was significantly larger than that of women with a natural delivery [(3.16±1.31) cm vs (2.58±0.47) cm, t=-2.082, P=0.038; (2.85±1.35) cm vs (2.00±0.64) cm, t=-2.828, P=0.007].

High frequency ultrasound can accurately and quantitatively evaluate diastasis recti abdominis, and the measurement of rectus abdominis distance in relaxation or contraction state has similar value. High frequency ultrasound can provide useful information for exploring the mechanism of diastasis recti abdominis and related influencing factors.