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Low birth weight associated with higher TSH levels among newborns
Small for gestational age newborns had higher thyroid-stimulating hormone concentrations than appropriate for gestational age newborns, researchers in Spain reported.
“Due to fetal growth restriction and an immature metabolism at birth, [small for gestational age] has been associated with several development disorders, including an increased risk of congenital hypothyroidism,” Vicente M. Bosch-Giménez, MD, PhD, of the department of surgery, pediatrics, obstetrics and gynecology at the University of Murcia in Spain, and colleagues wrote. “Because thyroid hormones are crucial for growth and neurocognitive development, some studies have compared thyroid function in [small for gestational age] and [appropriate for gestational age] based on the hypothesis that TSH concentrations differ between these two population groups.”
The researchers analyzed data from 5,819 preterm infants who were part of the Neonatal Congenital Hypothyroidism Screening Program, a national program with a participation rate of 99.9% of newborns in Spain, from 2008 to 2012. All infants born in the province of Alicante whose parents gave consent and who had a negative result for congenital hypothyroidism screening were included.
Slightly more than half (53.8%) of the newborns were male, 23.3% were twins and 3.3% had underweight. Mean TSH concentrations were 2.16 µIU/mL for infants who were small for gestational age and 1.8 µIU/mL for those with appropriate weight for gestational age (P = .012). Bosch-Giménez and colleagues reported a negative correlation between TSH levels and z score for the newborns’ weight (P < .001).
Besides being small for gestational age (P < .001), a multivariate analysis using weight as a qualitative variable found that Latin American mothers (P = .029), days of life at extraction (P < .001) and gestational age up to 28 weeks (P < .001) were all associated with TSH level. When researchers used z score for birth weight as a qualitative variable, the associations with TSH level were North African origin (P = .042), days of life at extraction, gestational age up to 28 weeks and z score for weight (P < .001 for all).
“In conclusion, our study suggests that TSH concentrations are higher in [small for gestational age] than in [appropriate for gestational age], and this should be taken into account when establishing an appropriate reference interval for [small for gestational age] infants,” the researchers wrote. “The clinical relevance remains unknown, but avenues of research have been opened that may allow a better understanding of long-term morbidities of these newborns.” – by Andy Polhamus
Disclosure: The researchers report no relevant financial disclosures.