Postpartum urinary retention can be caused by: a. Stretching of the ureters during delivery b. Decreased sensitivity to bladder fullness c. Contraction of bladder muscles caused by oxytocin d. The effects of proteinuria and lactosuria on the bladder

a. Stretching of the ureters during delivery

Explanation:

Postpartum urinary retention is defined as the stretching if the uterus or the genitourinary tissue which occurs in most of the women during vaginal deliveries. The postpartum bladder is vulnerable to the urinary retention. This occurs due to the physiological changes in the pregnancy period. During delivery through vagina, the genitourinary tissues becomes edematous and also gets traumatized form the labor process and thus stretches the ureters during the delivery time. But it returns to normal after 4 to 6 days of diagnosis.

Hence the correct option is (a).