Do any of my fellow preggers have an underactive thyroid and take medication?? I developed this as a result of my 1st pregnancy and that was 5 years ago. I have my levels checked regularly and actually just had them checked again just before I found out that I was pregnant. I have stayed at the same medication level for several years now which leads me to believe I have it well controlled. I read in a pregnancy book that a thyroid prob can cause mental retardation and low IQ???? Is anyone else dealing with this too???