Endocrine Abstracts

Evidence on whether neonatal thyroid screening results are dependent on maternal thyroid function is limited.

Objectives: To study the relationship between iodine status and maternal thyroid function in pregnancy, and neonatal screening results in a Northern Spanish population.

Methods: Prospective, longitudinal study of 297 pregnant women recruited in 2 obstetric centers of Pamplona (Spain) at the first antenatal visit, and their neonates. Serum thyrotropin (TSH), free thyroxine (fT4) and thyroid antibodies were measured in the three trimesters of pregnancy, and urinary iodine concentration (UIC) was measured in the first one. Neonatal TSH screening was performed in heel-puncture blood samples collected on filter paper, at 48–72 hours after birth. We analyzed the association between neonatal TSH values, and maternal UIC and thyroid function through pregnancy.

Results: Most pregnant women were caucasian (92.9%), mean age was 33.5±4.0 years-old, and 48.8% were nulliparous. Thyroid autoantibodies were positive in 63 women (21.2%). The maternal UIC in the first trimester was 243 mcg/L (133.5–395.5). The mean neonatal TSH was 1.7±1.4 mUI/L with 1.7% of neonates having TSH>5 mUI/L. Newborn TSH was higher in boys, and in offspring from older women (>30 year-old). Neonatal TSH values were correlated with maternal TSH only in the second trimester (P=0.043), and with maternal age (P=0.007). We found no association between neonatal TSH values and maternal thyroid function in the first and third trimester, maternal UIC, BMI, parity, birth weight or gestational age at delivery. We found no statistical differences in neonatal TSH values according to maternal iodine status, or according to thyroid autoimmunity.

Conclusions: In our population, only maternal TSH values in the second trimester correlated with newborn TSH. Maternal UIC was not associated with neonatal TSH at screening.