Neonatal thyrotropin concentration and iodine nutrition status of mothers: a systematic review and meta-analysis

Low maternal iodine intake disturbs the thyroid function of neonates transiently or permanently.

To our knowledge, we conducted one of the first systematic reviews and meta-analyses aimed at exploring the association of neonatal thyrotropin concentrations and iodine status of mothers during pregnancy and early postpartum periods.

Data were collected through literature searches for studies published between 1969 and 2015 with the use of electronic databases. Mean or median maternal urinary iodine and neonatal thyrotropin concentrations, along with other relevant data, were extracted from eligible studies. The quality and risk of bias of each study was assessed.

A random-effects model was used for the analysis. Of 110 studies identified, 25 trials were shown to be eligible for inclusion in the meta-analysis. Mean (95% CI) thyrotropin concentrations of neonates born to mothers with iodine deficiency were higher than in neonates born to mothers with iodine sufficiency during pregnancy in both heel blood samples [1.79 mIU/L (95% CI: 1.61, 1.97 mIU/L) compared with 1.75 mIU/L (95% CI: 1.68, 1.82 mIU/L), respectively] and cord blood samples [11.91 mIU/L (95% CI: 6.67, 17.14 mIU/L) compared with 6.15 mIU/L (95% CI: 4.30, 8.01 mIU/L), respectively]. There were no significant differences in neonatal thyrotropin concentrations of heel samples between mothers with iodine deficiency and those with sufficiency during the early postpartum period; however, the values of thyrotropin in cord samples of neonates born to mothers with iodine deficiency were significantly higher than in neonates born to mothers with iodine sufficiency [11.62 mIU/L (95% CI: 10.47, 12.77 mIU/L) compared with 7.40 mIU/L (95% CI: 6.21, 8.59 mIU/L)].

Our findings reveal that, compared with heel blood samples, neonatal thyrotropin in samples collected from the cord are more sensitive to the iodine status of mothers; however, further investigations are required in this regard.