We don't know (anyone who says they know is lying) and you need to do what your doctor says is best and not worry about your sway. Thyroid issues are one of the main causes of non-chromosomal losses in pregnancy and so you must take every caution to get your thyroid functioning as it should prior to TTC. I have seen NO correlation with thyroid and gender conceived, I have pink and blue swayers with all kinds of thyroid stuff going on and if there's any trend there it is so minor that it's impossible even for me to spot.