Thyroid hormone levels that are "normal" but not optimal can be problematic to fertility. Sub-clinical thyroid issues are one of the most common factors affecting hormones and fertility, as research has shown.
Too often I hear of those having their thyroid tested and then told it is normal, so they think that it could not be affecting them at all... only come to find out that they did not have all the necessary testing done or the levels are not where they should be to help their fertility.