Looking further at the issue, a study published in 2002 reported on Argentine researchers, who looked at 150 pregnancies among women ages 16 to 39 years who had a diagnosis of hypothyroidism while pregnant. Thirty-four percent of the women -- 51 pregnancies -- were hypothyroid when they conceived. Among them, 16 were overtly hypothyroid -- TSH more than 33.4 -- and 35 were subclinically hypothyroid -- TSH more than 12.9. A total of 99 pregnancies were conceived when the women were euthyroid -- normal TSH range -- and receiving thyroid treatment.
What the researchers found was that when treatment with levothyroxine was not sufficient -- meaning that the women had persistently elevated TSH levels -- the outcome of pregnancy was spontaneous abortion (miscarriage) in 60% of the overtly hypothyroid patients and in 71.4% of subclinically hypothyroid patients. Twenty percent of overtly hypothyroid patients and 7.2% of the subclinically hypothyroid had premature delivery. When treatment was sufficient and adequate, 100% of overtly hypothyroid patients and 90.5% of subclinically hypothyroid patients carried the pregnancies to term, with no miscarriages. Miscarriages, premature and term deliveries in patients who were euthyroid on levothyroxine at the time of conception were 4%, 11.1% and 84.9%.
Interestingly, another important finding of the researchers was that among patients taking levothyroxine for hypothyroidism prior to conceiving, Almost 70% had to increase their dose during pregnancy.
Overall, the researchers concluded that the success of a pregnancy doesn't depend on whether the hypothyroidism was overt or subclinical, but primarily on receiving adequate treatment.
Source:
Abalovich M, et. al. "Overt and subclinical hypothyroidism complicating pregnancy," Thyroid. 2002 Jan;12(1):63-8.
