The Evolving Biochemical Profile: From Low FT4/Low TSH to Isolated Hypothyroxinemia in Pregnancy
https://doi.org/10.15605/jafes.041.S1
- Author:
Wei Ton Wong
1
;
Muhammad Amir Arif Mohammad Nizam
1
;
Amila Syahida Rusli
1
Author Information
1. Internal Medicine Unit, Hospital Besut
- Publication Type:Journal Article
- MeSH:
Female;
Pregnancy;
Thyrotropin
- From:
Journal of the ASEAN Federation of Endocrine Societies
2026;41(S1):115-116
- CountryPhilippines
- Language:English
-
Abstract:
Introduction:Isolated hypothyroxinemia (IH) in pregnancy, characterized
by low free thyroxine 4 (FT4) with normal thyroidstimulating hormone (TSH), has a reported prevalence of
1.3–8%. We present a diagnostically challenging case that
initially mimicked central hypothyroidism before evolving
into classic IH.
Case:A 37-year-old G4P3 female at 22 + 3 weeks gestation
with β-thalassemia trait presented with palpitations and
tachycardia (150–184 bpm). A bedside echocardiogram
showed volume depletion. Her heart rate improved to 108–
116 bpm following a 1.5 L normal saline bolus. Incidentally,
thyroid function tests (TFTs) revealed both low FT4 6.04
pmol/L (7.86–14.41) and low TSH 0.009 mIU/L (0.38–5.33).
Anti-thyroid peroxidase antibody was markedly elevated
at 360 IU/mL (<35). At 24 + 4 weeks, TFTs showed persistently low FT4 (5.84
pmol/L) and TSH (0.022 mIU/L). Differential diagnoses
included central hypothyroidism or assay interference.
Tests were repeated using different platforms. Both the
Beckman system (FT4: 5.73 pmol/L, TSH: 0.086 mIU/L)
and Roche system (FT4: 8.83 pmol/L [12.0–22.0], TSH: 0.11
mIU/L [0.27–4.20]) confirmed low values, ruling out assay
interference. Following endocrinology consultation and
given her asymptomatic status, IH was considered most
likely, and a plan for close monitoring was initiated.
Serial follow-up demonstrated biochemical evolution. By
31 + 6 weeks, TFTs showed a low TSH (0.753 mIU/L) with
an FT4 level (5.86 pmol/L) within the normal reference
range, a pattern typical of IH in pregnancy. Repeat TFTs
6 weeks postpartum showed both TSH and FT4 within
normal range.
Conclusion:This case illustrates a rare and unexpected biochemical
progression of IH in pregnancy, initially presenting with
a pattern indistinguishable from central hypothyroidism.
It underscores that in an asymptomatic, fertile patient, IH
can manifest with an atypical pattern early in gestation. The
findings suggest that vigilant serial monitoring, rather than
immediate extensive pituitary workup, may be a prudent
initial approach in such scenarios, as the biochemical
profile can normalize toward the classic IH pattern as
pregnancy advances.
- Full text:2026080509212009148EP_A172.pdf
