Final answer:
After the evacuation of a molar pregnancy, it typically takes about 4 weeks for the beta-hCG levels to become undetectable.
Step-by-step explanation:
After the evacuation of a molar pregnancy, it typically takes about 4 weeks for the beta-hCG levels to become undetectable. This is because molar pregnancies, also known as gestational trophoblastic diseases, result in an abnormal growth of cells in the uterus. The beta-hCG hormone is produced by these abnormal cells and is responsible for maintaining the pregnancy.