Expectant mothers should be tested for thyroid issues to reduce their child’s risk of developing autism and other complications, experts say.  

New research published in the Annals of Neurology shows that mothers with low levels of the thyroid hormone T4, or throxine, are four times more likely to give birth to a child with autism. The more throxine deficient a mother is, the more pronounced her child’s symptoms can be, researchers said. 

Scientists from the Houston Methodist Neurological Institute and Erasmus Medical Centre came to this conclusion after studying 4,000 Dutch mothers and their children. This finding coincides with previous research that shows a mother’s throxine levels influence a child’s neurological development.

“It is increasingly apparent to us that autism is caused by environmental factors in most cases, not by genetics,” lead author Dr. Gustavo Román, a neurologist and neuroepidemiologist who directs the Nantz National Alzheimer Center, said in a press release. “That gives me hope that prevention is possible.”

Researchers say the most common cause of thyroid deficiency is a shortage of iodine in the diet. Because the U.S. introduced iodized table salt in the 1920s, only about one in seven Americans has hypothyroidism. Globally, one in seven people has low levels of throxine, according to the World Health Organization.

“If you are planning to become pregnant, have your doctor measure urine iodine and thyroid function beforehand,” Román advised. “If you have just become pregnant, have your doctor measure urine iodine, thyroid function, and begin using prenatal vitamins, making sure iodine is present.”

Other Perils of Low Hormone Levels in Pregnancy

While a child’s increased risk of autism due to a mother’s hypothyroidism, or low thyroid hormone levels, is a new consideration, experts have been aware of other complications related to the condition for some time.

A widely-cited 1988 study of complicated pregnancies showed that a mother’s untreated hypothyroidism can lead to several birth complications. These include preeclampsia, anemia, low birth weight, placental abruption, postpartum bleeding, and even the death of the baby.

Other studies of expectant mothers with hypothyroidism suggest correcting the imbalance with a synthetic version of thyroxine. One Swedish study monitoring throxine supplements in pregnant women advised doctors to begin with a low dose and increase it as needed, with regular monitoring, to ensure the best results.

However, no woman should begin taking any supplements while pregnant without first consulting her doctor.

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