RELATIONSHIP BETWEEN MODE OF DELIVERY AND NEONATAL THYROID HORMONE LEVELS AT BIRTH: A NARRATIVE REVIEW

Thyroid hormones are essential for normal development of fetus. After birth changes in thyroid hormone enable the neonate to be adapted for postnatal life. Accordingly, attention to the level of neonatal thyroid hormones at birth is important. Several maternal and environmental factors influence this adaption. Various studies have shown the association of different neonatal, maternal, and pregnancy-related factors with TSH in neonates. This review study was performed to investigate the relationship between delivery mode and labor pains with neonatal thyroid hormone levels at birth. In this narrative review, the PubMed, Web of Science and Scopus, as well as SID, Irandoc, and Magiran (Persian databases) were searched with appropriate keywords for the English and Persian related articles. In this narrative review that was conducted up to December 2019, of 67 records retrieved through primary searching databases, 14 eligible studies were evaluated. The majority of the studies (9 studies out of 13 studies) revealed that vaginal deliveries (instrumental or natural) lead to higher levels of cord TSH compared to elective cesarean section. It seems that stress during vaginal delivery may lead to elevated TSH in cord blood. These adaptations may act as a stimulus for rising the thyroid hormones in the first hours after the birth of neonates. This assumption needs to be evaluated by further comprehensive well-designed studies.