I did a little research on Turner’s syndrome. It is a serious chromosomal disorder where a woman ends up with a single X chromosome instead of the normal XX. According to what I read, they have to take hormones in order to develop like women. Women with Turner’s syndrome almost universally cannot produce eggs. The only way for them to have a baby is to use an egg from another female donor. This is against Church teaching, too. It sounds like it wouldn’t be an option anyway, since pregnancy is dangerous for this woman.
I also read that 99% of fetuses who have Turner Syndrome are spontaneously aborted through miscarriage. So I guess women with this syndrome should be consider it miraculous that they are alive!
I wonder if the real question is whether or not the person who started this thread would be happy marrying a woman who can’t give him any children. Birth control would probably not even be an issue. It would be the same as if he married someone who had a hysterectomy or who was past the age of menopause. There is no moral problem and no problem with the validity of the marriage.
For those who are afraid that taking hormones cause early abortions, I think it is obvious that the hormones are necessary for women with this syndrome. If there is no egg to fertilize, there will obviously be no early abortion.
If there is any chance that this woman could get pregnant, I would think that under the circumstances, she has an extremely serious reason to avoid pregnancy. It would probably be smart to go to an NFP class and learn all of the signs and symptoms, just in case. If there is no chance of pregnancy, there would be no reason to practice NFP (or any other method of birth control).