Acute urinary retention during pregnancy is rare. Retention secondary to an impacted, gravid uterus is an emergency. Retroversion of the uterus, a history of pelvic inflammatory disease, and large fibroids are predisposing factors. The enlarging gravid uterus and uterine fibroids may trap the uterus inside the pelvic ring, preventing it from ascending into the abdominal cavity; furthermore, a history of inflammatory disease may trap the fundus of the uterus within scar tissue that also may prevent the enlarging, gravid uterus from ascending into the abdominal cavity. The impacted uterus should be manually replaced in the anterior position. Clean intermittent catheterization and placement of a vaginal pessary are temporizing measures. A knowledge of the causes of urinary retention during pregnancy can help prevent spontaneous abortion and other devastating consequences that can arise as a result of a delay in the diagnosis.