Excess thyroid hormone associated with increased rates of miscarriage

August 10, 2004

CHICAGO - High levels of thyroid hormone in pregnant women can have a direct toxic effect on fetal development, according to a study in the August 11 issue of JAMA, the Journal of the American Medical Association.

According to background information in the article, thyroid hormone (TH) plays an important role in the development of the embryo and maturation of the fetus. Maternal hypothyroidism (an underactive thyroid gland) and hyperthyroidism (an overactive thyroid gland) have deleterious effects on the outcome of pregnancy. While the effects of TH deprivation on the fetus, independently from that on the mother, can be studied in infants with congenital hypothyroidism, this is not the case in those with fetal thyrotoxicosis (an overactive thyroid gland).

João Anselmo, M.D., of Hospital Divino Espírito Santo, Ponta Delgada, Azores-Portugal, and colleagues from the University of Chicago Hospitals studied the effects of TH excess on fetuses carried by mothers who, because of their resistance to TH (RTH) are normal despite high TH levels but who may carry normal fetuses that have been exposed to high maternal hormone levels. The study included 167 members of an Azorean family with RTH. Affected individuals had the RTH phenotype.

Thirty-six couples with complete information belonged to 1 of 3 groups: affected mothers (n=9), affected fathers (n=9), and unaffected relatives (n=18). "Mean miscarriage rates were 22.9 percent, 2.0 percent, and 4.4 percent, respectively. Affected mothers had an increased rate of miscarriage. They had marginally higher than expected numbers of affected offspring, i.e., 20 affected and 11 unaffected children, while affected fathers had 15 affected and 12 unaffected children. Unaffected infants born to affected mothers were significantly smaller than affected infants ...," the authors write. "Our data show a 3- to 4-fold increase in the rate of miscarriage in affected mothers compared with that of spouses of affected fathers or unaffected first-degree relatives ..."

"The data presented herein show, for the first time in humans, that high levels of TH can exert a direct toxic effect on fetal development. This is manifested by an increased rate of miscarriages and a lower birth weight of unaffected infants born to euthyroid mothers with high levels of TH. As expected, fetuses harboring a mutation that reduces the sensitivity to TH are protected from this toxic effect of TH excess.

Given the established importance of providing TH replacement to even mildly hypothyroid pregnant women, it is important to recognize that overreplacement appears to be equally detrimental," the authors conclude.
(JAMA. 2004;292:691-695. Available post-embargo at JAMA.com)

Editor's Note: This work was supported in part by grants from the National Institutes of Health. Dr. Refetoff is Academic Associate for Quest Diagnostics Inc.
-end-
For More Information: Contact the JAMA/Archives Media Relations Department at 312-464-JAMA (5262) or email: mediarelations@jama-archives.org.

Media Advisory: To contact corresponding author Samuel Refetoff, M.D., call John Easton at 773-702-6241.

The JAMA Network Journals

Related Infants Articles from Brightsurf:

Most infants are well even when moms are infected by COVID-19
Infants born to women with COVID-19 showed few adverse outcomes, according to the first report in the country of infant outcomes through eight weeks of age.

Probiotic may help treat colic in infants
Probiotics -- or 'good bacteria' -- have been used to treat infant colic with varying success.

Deaf infants' gaze behavior more advanced than that of hearing infants
Deaf infants who have been exposed to American Sign Language are better at following an adult's gaze than their hearing peers, supporting the idea that social-cognitive development is sensitive to different kinds of life experiences.

Initiating breastfeeding in vulnerable infants
The benefits of breastfeeding for both mother and child are well-recognized, including for late preterm infants (LPI).

Young infants with fever may be more likely to develop infections
Infants with a high fever may be at increased risk for infections, according to research from Penn State College of Medicine.

Early term infants less likely to breastfeed
A new, prospective study provides evidence that 'early term' infants (those born at 37-38 weeks) are less likely than full-term infants to be breastfeed within the first hour and at one month after birth.

Infants are more likely to learn when with a peer
Researchers at the University of Connecticut and University of Washington looked at the mechanisms involved in language learning among nine-month-olds, the youngest population known to be studied in relation to on-screen learning.

Allergic reactions to foods are milder in infants
Majority of infants with food-induced anaphylaxis present with hives and vomiting, suggesting there is less concern for life-threatening response to early food introduction.

Non-dairy drinks can be dangerous for infants
A brief report published in Acta Paediatrica points to the dangers of replacing breast milk or infant formula with a non-dairy drink before one year of age.

Infants can't talk, but they know how to reason
A new study reveals that preverbal infants are able to make rational deductions, showing surprise when an outcome does not occur as expected.

Read More: Infants News and Infants Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.