Thyroid Hormone Levels in Apparently Healthy Term Neonates at Birth and 72 Hours of Life in Abakaliki, Nigeria

Background. Congenital hypothyroidism (CH) is a major cause of preventable intellectual disability. The world incidence of CH is 1 in 4,000. Its incidence has increased over the past decades from 1:4,100 to 1:2,350. Undiagnosed cases, when severe, have serious effects such as severe impairment of linear growth, delayed puberty, irreversible neurological problems, and permanent intellectual disability. There is a need for a timely diagnosis at birth as well as timely treatment to avert the attendant irreversible brain damage. Neonatal thyroid function is influenced by the physiological TSH surge; hence, the timing of testing is vital for clear-cut screening. This study assessed thyroid hormone levels in apparently healthy term neonates at birth and 72 hours of life in Abakaliki, Nigeria. Methods. A prospective cross-sectional study of 168 consecutively delivered, apparently healthy term neonates was conducted. Serum thyroid-stimulating hormone (TSH), free thyroxine (fT4) and free triiodothyronine (fT3) were assayed at birth and 72-hours using Enzyme Linked Immuno- -Sorbent Assay. Congenital Hypothyroidism was defined as TSH > 10uIU/ml (ultra-sensitive ELISA) or fT4 < 10.3nmol/L (competitive ELISA). Results. Of the 168 neonates, 88 (52.4%) were females, and 80 (47.6%) were males. All were term and apparently healthy. Overall mean (standard deviation (SD)) Gestational age was 38.38 ± 0.77 (weeks). The cord blood and the venous blood mean (SD) serum concentrations of fT4 at birth and 72-hours were 16.89 ± 20.73 nmol/l and 20.91 ± 13.38nmol/l, the cord blood and the venous blood mean (SD) serum concentrations for fT3 at birth and 72-hours were 1.98 ± 1.13 pg/mL and 2.36 ± 1.80 pg/mL, while the cord blood and the venous blood mean (SD) serum concentrations for TSH at birth and 72-hours were 7.38 ± 4.96 mU/L and 3.82 ± 4.01 mU/L respectively. The 72-hour mean serum fT4 and fT3 were significantly higher than the cord blood levels (p = 0.001, 0.02), whereas TSH at 72 hours was significantly lower than the cord blood levels (p < 0.001). However, Low fT4 was found in 99 (58.9%) at birth and 19 (11.3%) at 72 hours. Median TSH was significantly higher at birth than at 72 hours (p < 0.001). Thyroid-stimulating hormone was greater than 7.0 uIU/mL in 68 subjects at birth and 32 (19.0%) subjects at 72 hours, respectively. However, 32 (19.0%) of these subjects had TSH values above 10.0 uIU/mL at birth, and 12 (7.2%) had values above 10.0 uIU/mL at 72 hours of birth, which suggests primary hypothyroidism. Hence, the prevalence of congenital hypothyroidism was 19.0% at birth and 7.2% at 72 hours. Conclusion. Thyroid-stimulating hormone levels were significantly higher at birth; however, declined considerably by 72 hours, reflecting the physiological neonatal TSH surge. Screening at 48–72 hours rather than at birth is more precise to reduce false positives. Locally validated neonatal reference intervals and confirmatory testing are crucial for the correct diagnosis of CH in Nigeria.