[Pregnancy in women with thyroid cancer treated with suppressive doses of L-thyroxine]

The aim of the study was to estimate the dose of thyroxine required by pregnant women who had undergone total thyreoidectomy and radioiodine treatment for thyroid cancer. Material consisted of 4 pregnant women, aged mean 30.8 years. One of patients was studied during 2 consecutive pregnancies. The daily mean dose of thyroxine was 175 micrograms. The control group consisted of 7 women with primary hypothyroidism aged mean 33.5 years, who were treated with replacement doses of thyroxine. One of them was pregnant twice. The mean daily dose of thyroxine was 106.3 micrograms. The estimation of TSH, fT4 were repeated every 4 weeks.

In all cases natural deliveries took place. All infants were alive and had no congenital malformations and no clinical or biochemical thyroid dysfunction was found. Pregnant women treated for thyroid cancer needed to have optimized their suppressive therapy by increasing the dose of thyroxine by 26% at the first trimester, 27% at the second and 38% at the last one. Statistically significant increase was found at the 1st trimester of pregnancy and it remained at the same level till the delivery. Pregnant hypothyroid women needed to have optimized their replacement thyroxine therapy by increasing of the dose by 53% at the first trimester, by 49% at the second and by 53% at the last one. Similarly to the 1st group of patients, we noticed statistically significant increase at the 1st trimester of pregnancy.

In pregnant women who have been previously treated for thyroid cancer the suppressive dose of thyroxine needs to be increased by 26-38% which is slightly less than the increase of the replacement dose in hypothyroid pregnant women.