What happens to the baby if the father is hypothyroid and the mother is hyperthyroid?

During pregnancy?: Do you mean during the pregnancy? The risk of preterm labor is higher if mom if hyperthyroid. If her thyroid antibodies are high, baby can be temporarily hyperthyroid at birth. Meds used for hyperthyroid can sometimes cause birth defects. If you mean long term effects on baby, having 2 parents with thyroid disease increases the likelihood baby will someday get it too.

Hard to predict: First, I agree with Dr Young's answer, and recommend very close followup for you thyroid condition during pregnancy. As far as the baby's chances for having thyroid problems, it would be nice if the hypo from dad & hyper from mom canceled each other out, but that is not how it works. Most likely both parents make antibodies targeting thyroid proteins, (continued)