In a new paper published in the journal Frontiers in Endocrinology, researchers assert that universal thyroid screening in early pregnancy holds promise for improving fetal and maternal outcomes.
Research has shown that maternal thyroid hormones are critical for a baby’s brain development. A fetus is completely reliant on thyroid hormones from its mother up to 16 weeks, a critical period for brain development.
Too much or too little can reduce later IQ, and increases the risk of premature birth, preeclampsia and other complications.
Unfortunately, thyroid levels are frequently abnormal in women of childbearing age. It is well-established that correcting symptomatic cases can protect both mother and baby from complications. And now, growing evidence shows that pregnant women with no symptoms could also benefit from thyroid screening.
“Fortunately, thyroid dysfunction is readily diagnosed with reliable blood tests and easily corrected with safe, inexpensive and available treatments,” says lead review author Dr. Peter Taylor of Cardiff University in the U.K.
“In fact, universal thyroid screening in early pregnancy fulfills most criteria for a beneficial and cost-effective screening program, and has already been implemented in countries like Spain, China and Poland.”
But other countries, including the U.K. and the U.S., opt instead for a “case-finding” approach. This means they screen only those women considered to be at high risk of thyroid dysfunction, based on clinical signs or symptoms, or a history of autoimmune diseases or preterm deliveries.
So why doesn’t everyone agree on universal thyroid screening in early pregnancy?
“Economic models show that universal screening is the most cost-effective approach, even if only obvious hypothyroidism (profoundly low thyroid hormone level) — which is often missed by case-finding — affects pregnancy and brain development,” said Taylor.
Overall, the debate hinges on the risks versus the benefits of treatment in cases where diagnosis is less certain; in women with abnormal or borderline thyroid tests, but who show no symptoms.
Unintentional overdiagnosis in borderline cases due to universal screening may lead to unnecessary patient anxiety and pressure on clinicians, as well as potential overtreatment which could negate benefits and has potential risks.
And although there is a strong link between mild hypothyroidism and acute negative outcomes such as pregnancy loss, there is a lack of high-quality trial evidence on the impact of thyroid hormone replacement in these cases.
One such trial showed that treatment of low-risk cases led to fewer pregnancy complications; two others found no effect on child IQ, but these initiated thyroid hormone replacement after the critical period for brain development, and therefore possibly too late to have had an impact.
What does this mean for pregnant women in case-finding countries like the U.S. and U.K?
“Universal thyroid screening in early pregnancy could improve child IQ and reduce complications of pregnancy. However, a consensus is unlikely to be reached without further controlled trials which recruit women pre-conception or as early as possible in pregnancy,” said Taylor.
“In the interim, the outcomes of existing universal screening programs will be crucial in gaining insights into the practicalities of this approach.”