Chart 2. Laboratory evaluation in the investigation of hypothyroidism in pregnancy.

	TSH	T4L	Diagnosis	ATPO
HYPOTHYROIDISM DIAGNOSED PRIOR TO PREGNANCY	≤2.5 mUI/L	Do not request (Result will not change management)	Properly treated hypothyroidism during pregnancy	Do not request (Result will not change management)
	>2.5 mUI/L		Hypothyroidism not properly treated during pregnancy
HYPOTHYROIDISM DIAGNOSED IN PREGNANCY	>10.0 mUI/L	Do not request (Result will not change management)	Overt hypothyroidism	Do not request (Result will not change management)
	>4.0 and ≤10.0 mUI/L	Within reference values informed by the laboratory	Subclinical hypothyroidism	Do not request (Proposed management in subclinical hypothyroidism is independent of ATPO)
	>4.0 and ≤10.0 mUI/L	Below the lower limit of reference informed by the laboratory	Overt hypothyroidism	Do not request (Result will not change management)
	>2.5 until ≤4.0 mUI/L	Within reference values informed by the laboratory	Euthyroidism	ATPO positive case (above the upper limit of reference informed by the laboratory), consider treatment
	≤2.5	Do not request (Result will not change management)	Euthyroidism	Do not request (Result will not change the proposed management for the first trimester in most patients)

TSH: thyroid stimulating hormone; FT4: free thyroxine; ATPO: antithyroperoxidase antibody; SCH: subclinical hypothyroidism.

Source: Prepared by the Working Group for Thyroid Dysfunctions in Pregnancy (CNEGAR and Brazilian Society of Endocrinology and Metabology – SBEM).