I also have never heard of a cord accident happening twice. Regarding luteal phase estrogen, or supplemental estrogen after a positive pregnancy test, there is not a great deal of convincing evidence that adding estrogen in the luteal phase or after a positive pregnancy test helps. Why not at least mention it to your RE and work with him/her to decide what you feel is the best thing? I would not be in favor of estrogen in the luteal phase - it might suppress LH hormone secretion from the pituitary gland, and LH is what drives the ovary to make progesterone, which in turn is important in maintaining a pregnancy.