Untreated hypothyroidism in pregnancy is associated with severe neurodevelopmental delay. Based on rodent experiments, maternal T3 is said not cross the placenta and to have little if any role in fetal brain development.Case report: A 36-year-old female with known hypothyroidism treated only with liothyronine (T3) 20 μg TDS. attended the antenatal clinic. It was suggested that she changed to treatment with levothyroxine (T4) or a combination of T3 and T4. However, she decided to continue on T3 only. Her booking thyroid function tests (TFTs) showed free T4 of 0.6, free T3 6.4 pmol/l and TSH 0.06 μ/l. In the second pregnancy the free T4 was 1.1, free T3 5.4 pmol/l and TSH 0.1 μ/l. Serial growth scans were normal throughout both pregnancies. Her first baby was forceps delivery with birth weight of 3065 g. Second baby was spontaneous vaginal delivery at term, with birth weight of 3685 g. Both children were euthyroid and were breast fed. Both children had normal physical and neurodevelopment as evidenced by normal growth scans during pregnancies, normal growth charts in the first years of life achieving all milestones for age and excellent school performances. Both siblings are currently progressing well in primary school.
Untreated hypothyroidism in pregnancy is associated with severe neurodevelopmental delay. Based on rodent experiments, maternal T3 is said not cross the placenta and to have little if any role in fetal brain development.
Conclusion: We were not able to identify any case where liothyronine was administered solely in all three trimesters. This case has shown normal neurodevelopment in both siblings. Maternal serum T3 concentrations were maintained within reference range while her serum T4 concentrations were very low i.e <2 pmol/l in both pregnancies. These pregnancies seem to challenge current dogma re thyroid hormone treatment during pregnancy.