Hello! I have gone carefully through your problem. As your all relevant tests are normal, you need not be so worried! Remember, abortion
does occur whenever the fetus is having congenital abnormality or is improperly developed, although there are many other causes as well.
I would suggest you to follow the advice given by your eminent gynecologist.
Serum FSH test is a hormonal
analysis of the important hormone 'Follicular stimulating hormone' & you should go for it & follow further instructions by your gynecologist. The results will be definitely positive & you should be relaxed now, as it does not seem to be a serious problem, especially when you are being under follow up of a competent gynecologist.
Thanks & take care of yourselves!