This study described the response of the bladder base (BB) by transabdominal ultrasound in primiparous women during movements that activate the abdominopelvic cavity musculature and cause variations in intra-abdominal pressure (IAP). A descriptive cross-sectional study was conducted in 64 primiparous women at eight weeks after uncomplicated delivery. BB displacement was measured using a 5-MHz convex transducer in a suprapubic position. Participants were asked to perform the isolated contraction of pelvic floor musculature (PFM) and transverse abdominis (TrA), cough at high lung volume and trunk flexion with and without maximal voluntary contraction of PFM. PFM contraction elevated the BB in all but one participant, whereas TrA contraction caused the BB to ascend in 56% of the women and descend in the rest; their combined contraction rose the BB in 65% of the women although the effect was greater with only PFM contraction (p < 0.01). The BB descended in all participants during coughing and trunk flexion although the descent was inferior with the joint maximal voluntary contraction of PFM (p < 0.01). In conclusion, TrA contraction must be assessed individually in puerperal women since its effect on the BB varies among subjects. During movements increasing IAP, such as coughing or curl-ups, the anticipatory contraction of PFM reduces bladder descent although not sufficiently to counteract bladder displacement.