MONDAY, Dec. 28, 2009 (HealthDay News) -- Low levels of a thyroid hormone in healthy pregnant women shortly before childbirth may be linked with fetal position problems that could require special care during delivery, new research finds.
"The link between thyroid dysfunction during pregnancy and difficulties during labor is well established," the lead author of the new study, Victor Pop, a research professor at the University of Tilburg in the Netherlands, said in a news release from the Society for Endocrinology. "However, to our knowledge, this is the first study to show an association between maternal thyroid hormone concentration during late gestation and fetal head position in healthy pregnant women with normal thyroid function."
At issue is whether thyroid hormone levels late in pregnancy are related to births in which the head of the baby is not in the normal delivery position, which is directed downward with the baby facing the mother's back at the start of labor. Other positions, including those in which the baby is facing the mother's belly, are considered abnormal delivery positions, the researchers explained.
The study looked at the thyroid levels of 960 healthy pregnant Dutch women and followed-up on their deliveries. The findings were published online Dec. 23 in Clinical Endocrinology.
Women with significantly higher levels of a specific thyroid hormone, called T4, at 36 weeks of pregnancy were more likely to present with a fetus in the normal delivery position, the study found. But women with lower levels of T4 at 36 weeks of gestation were more likely to need assisted delivery because of an abnormal fetal head position, it found.
"We believe that the relationship between thyroid hormone levels and fetal presentation at birth may be explained by recent findings that motor development in children is related to low maternal thyroid hormone concentration during pregnancy," Pop said. "It follows that impaired maternal thyroid function could also influence fetal motility and, therefore, rotation of the fetus during labor."
Further study is needed, he said, "to examine the relationship between maternal thyroid function and fetal presentation at birth in more detail."
The U.S. National Institutes of Health has more about the thyroid and pregnancy.