I had it too but only in my third pregnancy here at QEH, did they truly diagnose it as hyperthyroidism and treated me accordingly. I must say, that I suffered during the first 2 pregnancies. I had "morning sickness" for the first 2 trimesters and ended up in hospital a number of times due to dehydration. I lost anywhere between 5-10 kg in the pregnancies but since it was detected during the third pregnancy, I suffered less.
I went for bloody test with every check-up and was monitored closely. As a result to the condition, it was very hard for me to put on weight and I ended up having a c-section at 36 weeks for lake of weight gain. When my little girl was born, that was one of the things she was tested for because it seems that it can be passed on to them. Her levels were slightly elevated and they monitored her till she was 2 yrs to make sure that she did not have any form of thyroid problems. She went for blood test every 6 mths to make sure her levels were normal. Glad to say that she has just turned 2 and has a clean bill of health. My symptoms too disappeared after pregnancy.
I guess if you know before hand, it makes easier to manage the condition without the worry. I wished that I had been diagnosed much earlier so that I didn't have to suffer with my first 2 children.