Thyroid disease has been linked to menstrual irregularity, infertility, and miscarriage (as well as many other medical problems). I think that anyone with difficulty conceiving, irregular menses, or a history of miscarriage or preterm delivery should have TSH, free T4, and thyroid peroxidase antibody levels checked. Be careful if your doctor or nurse says your TSH level is OK, because even levels in the high-normal range (greater than 2.5) probably need to be treated.
Iodine is necessary for normal thyroid function, and more than one third of reproductive-age women in the US don’t get enough iodine. In my opinion, all women attempting pregnancy should take a prenatal vitamin that contains at least 150 mcg of iodine (and 220 mcg may be better). The iodine in the vitamin should be not be derived from kelp, as the levels of iodine in kelp vary dramatically. I recently made a trip to the CVS pharmacy, and I was disappointed to see that fewer than half of the prenatal vitamins contained iodine, and some of ones that did listed kelp as the iodine source. The only over-the-counter prenatal vitamin I found at CVS that had 220 mcg of iodine was Centrum Specialist Prenatal. (I have no financial ties to the company that makes this vitamin.) By the way, prescription prenatal vitamins are no more likely to have iodine than over-the-counter brands.