Widening of the inter-rectus distance (IRD) is highly prevalent among postpartum women and can lead to dysfunction of abdominopelvic muscles. The aim of this study was to evaluate the differences in IRD and abdominopelvic function between nulliparous, primiparous and multiparous women. A cross-sectional study was conducted on 75 women (25 nulliparous, 25 primiparous and 25 multiparous at 6 months postpartum). The participants underwent ultrasound assessment under three conditions (at rest, abdominal draw-in maneuver (ADIM) and curl-up) at two locations (2 cm above and 2 cm below the umbilicus). Furthermore, abdominopelvic muscle function was determined by prone, supine and side bridge tests. In all conditions and locations, the IRD were significantly higher (p < 0.05) in the primiparous and multiparous women than in the nulliparous. The multiparous women presented greater (p > 0.05) IRD at rest and during ADIM compared to the primiparous women. Regarding abdominopelvic muscle function, differences were only significant (p < 0.05) between the nulliparous with primiparous women in prone and supine conditions. These findings suggest that parity influences IRD: women at 6 months postpartum present greater IRD compared to nulliparous women; multiparous women present greater IRD at rest and during the activation of deep abdominal muscles than primiparous women; and primiparous women exhibit worse abdominopelvic muscle function than nulliparous women.