Look at effect of mild hypothyroidism in first and third trimester on maternal and pregnancy outcomes.
You have to dig a bit more on this one to get the goodies , but here they looked at mild hypothyroidism, so only one of TSH (Thyroid Stimulating Hormone) or T4 (serum-free thyroxine) being off while the other one is in normal limits. Low TSH in 3rd trimester leads to greater risk of pre-term labour, pre-eclampsia and fetal demise. Low T4 in both 1st and 3rd can lead to more pre-eclampsia and babys over 4500 g. Low 1st trimester T4 can lead to an increased rate of c-sections.
Link to Research