The ___ returns to its pre-pregnant size after delivery.

• A. Placenta
• B. Uterus
• C. Ovaries
• D. Urethra

Answer: (B)

After delivery, the uterus undergoes involution, shrinking back to its nonpregnant size. This happens as the myometrium contracts forcefully to compress blood vessels and autolyzes the excess decidual tissue left from pregnancy. The process is aided by oxytocin, which is released during breastfeeding and also produced naturally after birth, producing “afterpains” as the uterus contracts. Over the next several weeks, the uterus moves down from the abdomen into the pelvis and progressively returns to its pre-pregnant size, typically within about six weeks.

This is specific to the uterus. The placenta is expelled after birth and does not return to its pre-pregnant size. The ovaries resume normal function postpartum but are not described as returning to a pre-pregnant size in the same rapid, involutionary way. The urethra does not undergo a postpartum-size change related to involution.