The aim of this cross-sectional study in Jordan was to estimate the prevalence of hypothyroidism among women during early pregnancy and to assess the association of risk factors with hypothyroidism. According to internationally adopted thyroid stimulating hormone (TSH) and thyroxine (T 4 ) pregnancy reference ranges (TSH ≥ 2.6 mIU/L and T 4 10.6-20.4 pmol/L), 67 of 322 (20.8%) women were diagnosed with sub-clinical hypothyroidism. When the general laboratory criteria were applied (TSH ≥ 4.6 mIU/L and T 4 < 10.6 pmol/L) the prevalence dropped to 4.3%. No cases of overt hypothyroidism were diagnosed using either diagnostic criterion. Younger age and being in gestational weeks 1-8 were significant risk factors for hypothyroidism. It is suggested that the reference criteria need revision, and that pathology laboratories should adopt appropriate pregnancyspecific reference intervals.