Final answer:
Indomethacin is contraindicated at 33 weeks of gestation due to the risk of causing premature closure of the ductus arteriosus, a vital fetal blood vessel.
Step-by-step explanation:
The contraindication mentioned for the use of indomethacin at 33 weeks of gestation is A. Potential for premature closure of the ductus arteriosus. The ductus arteriosus is a fetal blood vessel that closes soon after birth. If it closes prematurely during fetal development, often as a result of exposure to certain medications like indomethacin, it can cause serious complications including heart problems and reduced blood flow to the lungs. Indomethacin is a nonsteroidal anti-inflammatory drug (NSAID) that can cause this adverse effect by blocking prostaglandin synthesis, which is necessary to keep the ductus arteriosus open until the appropriate time after birth.