Thyroid function of twin-pregnant women in early pregnancy

Abstract

Background:Serum human chorionic gonadotrophin (hCG) is higher in twin than that in singleton pregnancies. As hCG stimulates the thyroid to produce more free thyroxine (FT4), which may lead to decreased thyroid-stimulating hormone (TSH) levels, the reference ranges of thyroid-related indicators may differ between singleton and twin pregnancies in the first trimester. This study aimed to establish reference ranges for thyroid-related indicators in early twin pregnancies and to compare them with singleton pregnancies.Methods:Data of 820 twin-pregnant women were extracted from the established database of all pregnant women who delivered at Peking University First Hospital from October 2013 to May 2018; 160 who met National Academy of Clinical Biochemistry criteria were included to establish TSH and FT4 reference ranges. We screened 480 (3:1 paired) women with singleton pregnancies from the same database as controls. The Mann-Whitney test for TSH and FT4 levels was applied for comparisons between singleton and twin pregnancies.Results:First-trimester reference ranges (4–12 gestational weeks) for twin pregnancies were: TSH 0.69 (0.01–3.35) mIU/L and FT4 16.38 (12.45–23.34) pmol/L. Median TSH was significantly lower at 7 to 12 gestational weeks than that at 4 to 6 gestational weeks (0.62 vs. 0.96 mIU/L, Z = −1.964, P = 0.049); FT4 was not significantly different between the two groups. Compared to singleton pregnancies, median TSH was significantly lower (0.69 vs. 1.27 mIU/L, Z = −6.538, P = 0.000), and FT4 was significantly higher (16.38 vs. 14.85 pmol/L, Z = −7.399, P = 0.000) in twin pregnancies in the first trimester.Conclusions:Specific reference ranges for thyroid-related indicators for twin pregnancies are needed to avoid a misdiagnosis of thyroid dysfunction. Moreover, establishment of separate reference ranges for 4 to 6 and 7 to 12 gestational weeks in twin pregnancies may be considered.

Method-dependent variation in TSH and FT4 reference intervals in pregnancy: A systematic review

“…Nineteen studies excluded women with antibodies to either thyroid peroxidase (TPOAb) or thyroglobulin (TgAb), 13,14,17–20,22,31,33,34,36,39,41,44,45,47,51,52,55 while 24 studies did not measure TgAbs and excluded women with positive TPOAb only. 15,16,21,23–25,27–30,32,35,37,38,40,42,43,46,48–50,53,54 The median age of patients ranged from 24 to 35 years with TSH and FT4 reference intervals determined during the first, second and third trimesters in 42, 28 and 26 studies, respectively. Studies that presented data separately for patients with different ethnicities and with multiple assay methods are presented separately.…”

Maternal thyroid function in multiple pregnancies – a systematic review

“…The comparison of TSH levels between SP and TP/MP in the 1 st trimester of pregnancy was available in 8 studies. In 5 cases, a lower TSH level in the 1 st trimester was found in SP compared to TP (25,36,37,39,40). Such a phenomenon was not confirmed by Grün et al, Sakaguchi et al and Ogueh et al, but their studies were characterized by the lowest number of participants among the included papers (33)(34)(35).…”

“…The implemented search strategy facilitated the identification of 12 eligible articles (25,30,31,(33)(34)(35)(36)(37)(38)(39)(40)(41). They were published between 1997 and 2022.…”

“…The number of examined women with MP ranged from 9 to 1 626 in individual studies. All the studies included TSH measurement results (25,30,31,(33)(34)(35)(36)(37)(38)(39)(40)(41), 11 out of 12 -FT4 results (25,30,31,(33)(34)(35)(37)(38)(39)(40)(41), and 2 out of 12 -FT3 results (34,38). Half of the studies concurrently examined HCG and/or its subunits (25, 33-35, 37, 38).…”

“…TSH examination was performed in 11 out of the studies (25,30,31,(33)(34)(35)(36)(37)(38)(39)(40). The comparison of TSH levels between SP and TP/MP in the 1 st trimester of pregnancy was available in 8 studies.…”