Final answer:
The nurse should inform the client that pooling of lochia is normal when first getting out of bed post-delivery and offer reassurance (option A).
Step-by-step explanation:
The nurse should reassure the client that passing a large amount of lochia is not uncommon when getting out of bed for the first time after delivery. Lochia can indeed pool in the vagina while lying down, leading to a sudden gush when standing up. Uterine lining cells, erythrocytes, leukocytes, and other debris make up lochia, which evolves from lochia rubra to lochia serosa and finally to lochia alba during the postpartum period. The correct response for the nurse to provide would be option A, "Lochia can pool in the vagina while you lie in bed, which might explain the large amount you experienced upon standing," as this option offers a normal explanation and reassurance.
Hence, the answer is option A.