Final answer:
The most likely cause of a late postpartum hemorrhage is D. Uterine subinvolution, which occurs when the uterus doesn't properly contract to reduce bleeding.
Step-by-step explanation:
The complication most likely responsible for a late postpartum hemorrhage is D. Uterine subinvolution. Postpartum hemorrhage that occurs 24 hours to 12 weeks after delivery is characterized as late or secondary. One of the main causes is when the uterus does not contract strongly enough to compress the blood vessels where the placenta was attached, which is known as uterine subinvolution.
During the postpartum period, the uterus should contract and return to its pre-pregnancy size through a process called involution. This process helps to prevent excessive bleeding by compressing the blood vessels in the uterine lining. Breastfeeding can aid in this process, as it stimulates the release of oxytocin, a hormone that triggers uterine contractions. However, if parts of the placenta remain in the uterus, they can interfere with uterine contractions and involution, leading to hemorrhage. Therefore, obstetricians must ensure that the expelled placenta and fetal membranes are intact to prevent this complication.
Cervical and perineal lacerations, though potential causes of immediate postpartum hemorrhage, are less likely to be the cause of late postpartum hemorrhage. Clotting deficiencies can contribute to hemorrhage, but they are not as directly related to late postpartum hemorrhage as uterine subinvolution is.