title: The relationship of preconception thyrotropin levels to requirements for increasing the levothyroxine dose during pregnancy in women with primary hypothyroidism.
abstract: BACKGROUND
  Most women with hypothyroidism require an increase in their dose of levothyroxine (LT4) after conception. To minimize fetal and maternal complications of maternal hypothyroidism, it is thought that women should be rapidly restored to the euthyroid state. The objectives of this study was to determine the percentage of hypothyroid women who would need to increase their dose of LT4 dose even if they had a preconception (pre-C) serum thyrotropin (TSH) of <2.5 mIU/L as recommended by the Endocrine Society's guidelines and to ascertain whether there was a relationship between the pre-C TSH value and the need to increase the LT4 dose during pregnancy.
  
  
  METHODS
  Fifty-three pregnant women with hypothyroidism on LT4 treatment in whom the pre-C serum TSH was <2.5 mIU/L, but which was within the normal range, within the 6 months before pregnancy were retrospectively studied. An additional selection criterion was that their LT4 dose at the time of their first prenatal visit was the same as that received pre-C.
  
  
  RESULTS
  Seventeen patients had to increase their LT4 dose during pregnancy, because their serum TSH was increased at the time of the first prenatal visit (Group 1); and 36 patients did not have to increase their dose of LT4 during pregnancy (Group 2). The pre-C TSH was significantly higher in Group 1 (1.55 ± 0.62 mIU/L) than in Group 2 (0.98 ± 0.67 mIU/L). When pre-C TSH range was 1.2-2.4 mIU/L, 50% of the patients required an increase in the LT4 dose during pregnancy. In contrast, when the pre-C TSH was <1.2 mIU/L, only 17.2% (p< 0.02) had to increase the LT4 dose during pregnancy.
  
  
  CONCLUSIONS
  We suggest that in women with hypothyroidism who are planning to become pregnant, serum TSH levels should be in the normal range but should not be greater than about 1.2 mIU/mL.
authors.affiliation: Endocrinology Division, Hospital Carlos Durand, Diaz Velez 5044, Buenos Aires, Argentina. mabalovich@yahoo.com.ar
authors.forename: Marcos
authors.initials: M
authors.lastname: Abalovich
authors.forename: Graciela
authors.initials: G
authors.lastname: Alcaraz
authors.forename: Jessica
authors.initials: J
authors.lastname: Kleiman-Rubinsztein
authors.forename: María Magdalena
authors.initials: MM
authors.lastname: Pavlove
authors.forename: Cecilia
authors.initials: C
authors.lastname: Cornelio
authors.forename: Oscar
authors.initials: O
authors.lastname: Levalle
authors.forename: Silvia
authors.initials: S
authors.lastname: Gutierrez
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000097:blood / Q000188:drug therapy*; D011247:Pregnancy; D011248:Pregnancy Complications / Q000097:blood* / Q000188:drug therapy*; D012189:Retrospective Studies; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000008:administration & dosage / Q000627:therapeutic use*
chemical_list: D013972:Thyrotropin; D013974:Thyroxine