Table 2.
Basic characteristics of the retrieved studies.
| Authors, year and country of publication | Main aim of the study | Population of pregnant women | Data on thyroid function | Parameters | Time-points |
|---|---|---|---|---|---|
|
Grün, Meuris et al.
1997 Belgium |
To examine the thyrotropic role of HCG in early TP | 17 SP 13 TP All after IVF |
No history of thyroid disease, no ATA | HCG, α-HCG, β-HCG, TSH, FT4, ATA | GWs: 6, 8, 9, 10, 11, 15, 19, 22, 32 |
|
Sakaguchi, Yoshimura et al.
1998 Japan |
To evaluate thyroid function and the thyrotropic action of HCG in MP |
27 SP (age 23-38) 9 MP (6 TP, 3 TrP) (age 26-37) |
No history of thyroid disease | HCG, α-HCG, β-HCG, TSH, FT3, FT4, TSA |
Trimesters: 1st, 2nd, 3rd |
|
Ogueh, Hawkins et al.
2000 the United Kingdom |
To examine maternal TSH, FT4 and HCG in MP before and after embryo reduction |
group 1
(12 SP, 12 TP after IVF-ET) group 2 (39 MP (3-8 fetuses)) undergoing fetal reduction to TP) |
No data | TSH, FT4, HCG | GWs: 10–12 (before fetal reduction), 4 weeks after, 8 weeks after |
|
Dashe, Casey
et al. 2005 the United States of America |
To estimate the reference range for TSH in SP and TP | 13 599 SP (89% aged 18-35) 132 TP (90% aged 18-35) |
No data | TSH | 42% by 12 GWs, 69% by 20 GWs, 95% by 37 GWs |
|
Ashoor, Muto
et al. 2013 the United Kingdom |
To establish reference ranges of maternal serum TSH and FT4 at 11–13 GWs of TP |
235 TP
(177 DC; (median age 33.7), 58 MC with normal outcomes (median age 33.6), 19 MC complicated by severe TTTS (median age 32.6) |
No history of overt thyroid disease; 84.3% negative TPOAb and TgAb |
β-HCG, TSH, FT4, TPOAb, TgAb | GWs: 11-13 DC & MC median 13.0 TTTS median 12.5 |
|
Hanaoka, Arata et al.
2015 Japan |
To study the relationship between maternal serum HCG and thyroid function in TTTS |
131 TP
All with TTTS = MC |
No data | HCG, TSH, FT3, FT4 | GWs: 16-26 (before operation) 2 weeks after, 4 weeks after |
|
Rosner, Fox et al.
2017 the United States of America |
To determine if the treatment of overt hypothyroidism in TP reduced the adverse outcomes |
612 TP
Hypothyroid (n = 85; mean age 35.3) Healthy n = 527 (mean age 34.0) |
13.9% of overt hypothyroidism at treatment initiation, all treated until TSH reached <2.5 IU/ml | TSH, FT4 | At the beginning of prenatal care (not specified) |
|
Šálek, Dhaifalah et al.
2018 the Czech Republic |
To establish maternal TSH reference ranges for 1st trimester screening from 11 + 0 to 13 + 6 GWs | 10 592 SP (median age 29) 201 TP (median age 31) |
No history of thyroid disease Adequate iodine supply assumed (iodized salt in the Czech Republic since 1947) |
TSH, FT4, TPOAb | SP median 12 GWs + 4 days TP median 12 GWs + 5 days |
|
Šálek, Dhaifalah et al.
2019 the Czech Republic |
To determine the prevalence of maternal hypothyroidism at 11-14 GWs and to compare the rates for SP and TP | 4 965 SP (median age 30) 109 TP (median age 31) |
TSH, FT4, TPOAb | SP & TP median 12 GWs + 5 days |
|
|
Jiang, Sun et al.
2019 China |
To establish reference ranges for thyroid-related indicators in early TP and to compare with SP | 480 SP (median age 30) 160 TP (median age 31) • n = 21 at 4-6 GWs • n = 139 at 7-12 GWs |
No history of thyroid disease or thyroid-interfering medications, IVF, TPOAb positivity, adequate iodine supply assumed basing on (42, 43) |
TSH, FT4, TPOAb | SP & TP median 9 GWs |
|
Chen, Yang et al.
2021 China |
To evaluate thyroid function in TP and compare with SP | 46 834 SP (median age 30) 1 208 TP (median age 31) |
No history of thyroid disease, TPOAb positivity, SP - 10.3% TP - 10.8% |
HCG, TSH, FT4, TPOAb | Early GWs: 8-14 Late GWs: 28-35 |
|
Liu, Su et al.
2022 China |
To study the association of TH and birth weight in TP |
1 626 TP
(81.1% <35 years) 72.4% DC 27.6% MC |
No history of thyroid disease or taking thyroid-interfering medications, TTTS or ART | TSH, FT4, TPOAb | 64.1% in the 1st trimester 32.8% in the 2nd trimester 3.1% in the 3rd trimester |
ART, assisted reproductive techniques; ATA, anti-thyroid antibodies; DC, dichorionic; GW, gestational week; HCG, human chorionic gonadotropin; IVF-ET, in vitro fertilization and embryo transfer; FT3, free triiodothyronine; FT4, free thyroxine; MC, monochorionic; MP, multiple pregnancies; SP, single pregnancies; TFT, thyroid function test; TgAb, anti-thyroglobulin antibodies; TH, thyroid hormones; TP, twin pregnancies; TPOAb, anti-thyroid peroxidase antibodies; TSA, thyroid stimulating activity; TSH, thyroid stimulating hormone; TTTS, twin-to-twin transfusion syndrome.