Is the reason a married woman is currently unable to conceive due to her vow to deprive herself of childbearing if she were to return to committing the sin from which she repented, and will this deprivation continue?

This might be a bad omen due to violating the Prophet's — peace and blessings be upon him — prohibition against supplicating against oneself, one's children, and one's wealth, because that might coincide with a time of answered prayers. Therefore, the woman should seek forgiveness, strive in supplication, take the necessary means, and have a good opinion of Allah so that He may bless her with righteous offspring.