Researchers from Charles University in Prague, Czech Republic found that over one third of mothers who had a common autoimmune response in pregnancy went on to develop thyroid problems after birth.
About one in seven pregnant women suffer this immune response, suggesting about 5% of all mothers will later suffer thyroid disorders.
Researchers called for women who test positive for this immune response to be tested for thyroid function after delivery to detect disorders earlier.
Many tens of thousands of women in large European countries such as the UK may have thyroid problems caused by this response that could have been detected earlier with a simple test, they argued.
The team assessed 822 pregnant women with thyroid problems during the first trimester.
They measured levels of antibodies for thyroid peroxidase (TPO), a key enzyme involved with hormone production, as well as thyroid stimulating hormone (TSH) and other markers of thyroid function.
They found that 36% of women with antibodies for TPO had low TSH at the end of the study.
Researchers said current follow-up and treatment of these women were insufficient. They suggested that women with this antibody should be closely monitored after delivery even if they have normal thyroid function during pregnancy.