The Correlation Between Subclinical Hypothyroidism Before 20 Weeks Of Pregnancy And Miscarriage:A Meta Analysis

Purpose: The Correlation between subclinical hypothyroidism before 20 weeks of pregnancy and miscarriage are still conflicting.This meta-analysis was used to evaluate the association between subclinical hypothyroidism before 20 weeks of pregnancy and the risk of miscarriage.Methods: We searched the PubMed、EMbase、Cochrane Library、Web of Science、CNKI、WanFang、CBM databases through January 2018 to identify researches.Two reviewers independently screened literature,extracted data,and assessed the risk of bias of included studies.Quality of evidence was assessed per outcome,using GRADE.From the studies matched,the relative risk(RR)and corresponding 95% confidence interval(95% CI)were calculated to yield outcomes.And was performed with STATA 12.0 and RevMan5.3 software.Results: A total of 14 population-based studies including 33,640 participants were identified as eligible for this meta-analysis.A meta-analysis of 11 researches illustrated that non-treatment SCH was related to the risk for miscarriage(Relative Risk [RR]= 1.89,95%Confidence Interval [CI] 1.60–2.24,P < 0.05).In addition,according to the subclinical hypothyroidism were defined by 2 kinds of general diagnostic criteria(ATA diagnostic criteria and specific diagnostic criteria),SCH patients in the ATA diagnostic criteria group[RR=2.04,95%CI(1.66,2.51),P < 0.05] were more likely to suffer miscarriages than those in the specific diagnostic criteria[RR=1.60,95%CI(1.19,2.15),P < 0.05].Five researches illustrated SCH pregnant with treatment was also not related to the risk of miscarriage[RR=1.14,95%CI(0.82,1.57),P = 0.44].Compared to isolated SCH pregnant,SCH patients with thyroid autoimmunity(TAI)had a higher incidence of miscarriage[RR=2.69,95%CI(1.94,3.73),P < 0.05].Conclusions: SCH is a risk factor for abortion before 20 weeks of pregnancy and treatment can reduce the rate of abortion.According to the ATA diagnostic standard(serum TSH level >2.5 m IU / L),that can increase the rate of abortion.At present,the specific mechanism that subclinical hypothyroidism could increase the risk of abortion is not clear,and further studies are needed.