Doubts and Concerns about Isolated Maternal Hypothyroxinemia

Table 1

Biochemical criteria used to define isolated maternal hypothyroxinemia and its epidemiological impact.

Author (reference number) (year) Country	Lower FT4 percentile (pmol/liter)	Manufacturer’s FT4 reference range (pmol/liter)	Upper TSH limit (mU/liter)	Manufacturer’s TSH reference range (mU/liter)	Prevalence of isolated hypo-thyroxinemia (%)	Gestational age of hypo-thyroxinemia assessment
Pop et al. [5] (1999); The Netherlands	10th; (1st tr. 10.4)	8.8–18.0^a	2.0	0.15–2.0	NR
Pop et al. [6] (2003); The Netherlands	10th; (1st tr. 12.4)	8.7–19.6^a	2.0	0.15–2.0	NR
Kooistra et al. [7] (2006); The Netherlands	10th; (NR)	8.7–19.6^a	2.0	0.15–2.0	NR
Casey et al. [10] (2007); USA	2.5th; (GW 6-20 11.1)	11.2–24.7^b	3.0	NR	1.3%	1st half of gestation
Vaidya et al. [11] (2007); UK	2.5th; (1st tr. 10.6)	12.0–23.0^c	3.0	0.27–4.2	1.6% (7.8%*)	1st trimester
Cleary-Goldman et al. [13] (2008); USA	2.5th; (1st tr. 9.3; 2nd tr. 9.3)	10.3–24.4^b	1st trim 4.28. 2nd trim. 3.93	NR	2.1%; 2.3%	1st trimester 2nd trimester
Moleti et al. [12] (2009); Italy	2.5th; (1st tr. 11.9; 2nd tr. 10.4; 3rd tr. 10.3)	11.7–22.0^d	1st tr. 2.3; 2nd tr. 2.8; 3rd tr. 3.0	0.4–4.0	3.2%; 12.7%; 9.5%	1st trimester 2nd trimester 3rd trimester
Berbel et al. [8] (2009); Spain	10th (10.5)	9.1–23.8^e	4.8	0.38–4.8	23.9%; 20.6%; 26.5%	1st trimester 2nd trimester 3rd trimester
Shan et al. [14] (2009); China	2.5th; (GW 4 14.1; GW 8 11.9; GW 12 11.4; GW 16 12.3; GW 20 11.6)	10.3–24.5^b	GW 4 4.38; GW 8 3.8; GW 12 2.96; GW 16 3.29; GW 20 3.88	0.3–4.8	2.2% (0.4%*)	1st half of gestation
Henrichs et al. [9] (2010); The Netherlands	10th; (11.76); 5th (10.96)	11.0–25.0^f	2.5	NR	8.5% (<10th); 4.3% (<5th)	GW 13 (median)

*According to manufacturer’s FT4 reference range; GW: gestational week; NR: not reported.
^aEnhanced chemiluminescence immunoassay, Amerlite-MAB (Kodak Clinical Diagnostics, Amersham, UK); ^bchemiluminescent immunoassay, Immulite 2000 Analyzer (Diagnostic Products Corporation, Los Angeles, CA); ^celectrochemiluminescent immunoassay, Modular E 170 Analyzer (Roche Diagnostics Ltd., Lewes UK); ^delectrochemiluminescence immunoassay, Modular E 170 Analyzer (Roche Diagnostics GmbH, Mannheim, Germany); ^echemiluminiscence immunoassay, ADVIA Centaur-XP immunoassay system (Siemens Medical Solutions Diagnostics Ltd., Llamberis, UK); ^fenhanced chemiluminescent immunoassay, Vitros ECI Immunodiagnostic (ORTHO Clinical Diagnostics, Rochester, NY).