Thyroid antibody titer and avidity inpatients with recurrent miscarriage

Rhoda Wilson, Ph.D.,* Huang Ling, Ph.D.,* Marjorie A. MacLean, M.D.,*John Mooney, Ph.D.,*† Denis Kinnane, M.D.,*† James H. McKillop, M.D., andJames J. Walker, M.D.‡

Glasgow Royal Infirmary and Glasgow Dental Hospital, Glasgow; and St. James University Hospital,Leeds, United Kingdom

Objective: To determine whether the titer and avidity of the thyroid peroxidase antibody differs betweenpregnant women in their first trimester who have a history of recurrent miscarriage and whose pregnanciescontinue to term and those whose pregnancies fail again later in the first trimester.

Design: Controlled clinical study.

Setting: Healthy volunteers in an academic research environment.

Patient(s): Pregnant women in their first trimester who had a history of recurrent miscarriage ($3 miscar-riages) and who were known to be positive for the thyroid peroxidase antibody.

Intervention(s): None of the patients received any medication.

Main Outcome Measure(s): Thyroid peroxidase antibody titer and avidity (i.e., the net binding strengthbetween antibody and antigen).

Result(s): At the time of presentation, thyroid peroxidase antibody titer and avidity was significantly higherin those women who later miscarried compared with those whose pregnancies continued. In those whosepregnancies continued to term, titer and avidity declined as the pregnancy progressed.

Conclusion(s): Autoimmunity plays a role in recurrent miscarriage. Among a group of patients who had hadrecurrent miscarriages, there appeared to be differences in the humoral response to the pregnancy betweenthose whose pregnancies continued to term and those whose pregnancies failed again. (Fertil Sterilt 1999;71:558–61. ©1999 by American Society for Reproductive Medicine.)

Key Words: Recurrent miscarriage, autoimmunity, thyroid peroxidase antibody

The causes of recurrent miscarriage are notyet fully understood, but previous studies havesuggested that immunologic and/or autoim-mune mechanisms may be involved (1, 2).Pregnancy loss seems to occur with increasedfrequency in the presence of abnormal autoim-mune function. This association first was madewith reference to lupus anticoagulant and otherphospholipid antibodies (3).

There now have been several reports in theliterature of an increased incidence of thyroidantibodies in the sera of women with a historyof recurrent miscarriage (4, 5), and it has beensuggested that thyroid antibodies may serve asa marker for women at risk for miscarriage. Wealso recently reported an increased incidence ofthe antibody that produces B-cell subsetCD5/20 in women with a history of recurrentmiscarriage (6).

The aim of this study was twofold: to com-pare the titer of thyroid microsomal antibodiesin pregnant women with a history of recurrentmiscarriage who had successful pregnancieswith those whose pregnancies were not suc-cessful and to examine antibody avidity (i.e.,the net binding strength between antibody andantigen). Avidity has been shown to be a usefulindicator of the biologic function of antibodiesin autoimmunity and B-cell activation (9, 10).

MATERIALS AND METHODS

PatientsThis study was approved by our ethics com-

mittee.

Fifteen pregnant women (6.66 1.8 weeks’gestation) with a history of recurrent miscar-riage ($3 previous miscarriages) were enrolled

Received March 6, 1998;revised and acceptedNovember 10, 1998.Reprint requests: RhodaWilson, Ph.D., Departmentof Medicine, GlasgowRoyal Infirmary, 10Alexandra Parade,Glasgow G31 2ER, UnitedKingdom (FAX: 0141-211-2953.* University Department ofMedicine, Glasgow RoyalInfirmary.† Department ofPeriodontology, GlasgowDental Hospital.‡ Department of Obstetricsand Gynaecology, St.James University Hospital.

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in the study. All of them were negative for antinuclear andantiphospholipid antibodies. Of the 15 patients, 7 miscarriedlater in the first trimester (group 1) and 8 carried theirpregnancy to term (group 2). Patients in group 1 had a mean(6SD) age of 29.46 3.4 years and had had a mean (6SD)of 4.1 6 1.5 previous miscarriages. Patients in group 2 hada mean (6SD) age of 20.76 2.7 years and had had a meanof 4.6 6 2.2 previous miscarriages. All the women werepositive for thyroid peroxidase (TPO) antibodies and allwere euthyroid at the time of sampling.

MethodsSamples were tested for thyroid microsomal antibodies as

described previously (6) with the use of ELISA kits (RSRLtd, Cardiff, Wales, UK). Briefly, positive controls, stan-dards, and patient samples were run in duplicate. Sampleswith values of.1 U/mL were considered positive for thy-roid antibodies.

Thyroid avidity studies were performed according to themethod of Mooney et al. (7). Briefly, after incubation of theserum in 96-well microtiter plates, the wells were treatedwith increasing concentrations of ammonium thiocyanate(0.2–8 M) and the concentration required to dissociate 50%of the bound antibody was determined by linear regressionanalysis.

RESULTS

The results (Fig. 1) showed that in women with a historyof recurrent miscarriage who were positive for the TPOantibody, the antibody titer was significantly higher(P,.03) at thetime of presentation in those who miscarriedlater in the first trimester (group 1) than in those who carriedtheir pregnancy to term (group 2). There was no correlationbetween the number of miscarriages and the antibody titer.In those women whose pregnancies did continue to term(group 2), the antibody titer decreased significantly through-out the remainder of the pregnancy (Fig. 2).

Antibody avidity studies revealed that TPO avidity alsowas increased significantly (P,.006) in women with ahistory of recurrent miscarriage whose pregnancies againfailed later in the first trimester compared with those whosepregnancies continued to term (Fig. 1). Antibody avidity,which was low in all women with successful pregnancies,increased in the second trimester before decreasing again inthe third trimester (Fig. 2).

DISCUSSION

In recent years, interest in the role of autoimmune thyroiddisease in pregnancy has increased. We studied patients who

F I G U R E 1

Thyroid peroxidase avidity (A) and titer (B) in group 1 and group 2 patients. *P,.006. The difference in thyroid peroxidase aviditybetween groups 1 and 2 was statistically significant. 1P,.03. The difference in thyroid peroxidase titer between groups 1 and2 was statistically significant.

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were known to be positive for the TPO antibody. The levelof this antibody was significantly higher in women whosubsequently miscarried than in those who carried theirpregnancies to term. These findings are in agreement withthose of previous studies.

In one of the largest studies of its type, Stagnaro-Green etal. (8) tested 552 women and found that 20% of them werepositive for thyroid antibodies. Of these antibody-positivewomen, 17% miscarried, compared with only 8.4% of theantibody-negative women. Unlike in our study, however,these investigators did not consider whether the women whomiscarried were doing so for the first time or whether theyhad a history of miscarriage. Singh et al. (4) studied thyroidantibody status in 487 pregnant women and found that 22%of them were positive for TPO, antithyroglobulin antibodies,or both. They concluded that thyroid antibodies may be auseful marker for identifying women at risk for clinicalmiscarriage. Similar conclusions were drawn in the smallerstudy by Bussen and Steck (5), who again found the inci-dence of thyroid antibodies to be significantly increased inwomen with recurrent miscarriage.

In an earlier study, Pratt et al. (11) investigated theincidence of thyroid antibodies before and after pregnancy in42 nonpregnant women with a history of recurrent miscar-riage. They found that 31% of the women were positive for

thyroid antibodies before becoming pregnant, and that 67%of these women subsequently miscarried again.

It is possible that the presence of thyroid antibodies maysimply indicate abnormal T-cell function in these womenand that it is this abnormal function, and not the antibodies,that is responsible for the loss. This is in keeping with theresults of previous studies in which we found increasedlevels of interleukin-2 receptor in the serum of women whomiscarried. Levels of interleukin-2 receptor are known to beindicators of increased immunologic activity.

Although this study showed that the antibody titer wassignificantly higher in patients who miscarried, it alsoshowed that in patients whose pregnancies continued, theantibody titer decreased as the pregnancy progressed. To ourknowledge, no previous study has examined changes inantibody titer throughout the course of a continuing preg-nancy. Kwak et al. (12) evaluated levels of antiphospholipidantibodies and found that they remained stable in patientswhose pregnancies continued but rose in patients whosepregnancies failed.

Significantly increased avidity was found in the womenwho miscarried. Since antibody avidity is related to thebiological function of the antibody, it would appear that theimmune system had been activated in the women who mis-carried.

The results of this study suggest that immunologic andautoimmune mechanisms play a role in recurrent miscar-riage. However, the study did not distinguish between causeand effect, although it did suggest that thyroid antibodiesmay be a marker for at-risk pregnancies. These changes wereobserved early in the first trimester of the pregnancy. It is notclear why, in a group of unselected and untreated patientswith recurrent miscarriage, approximately 50% should mis-carry and 50% should have a successful pregnancy. It ap-pears that in those whose pregnancies continued, there wasdown-regulation of antibody production.

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F I G U R E 2

Changes in thyroid peroxidase avidity and titer during preg-nancy. *P,.02. The difference in thyroid peroxidase avidity(dashed line) versus titer (solid line) in group 1 versus group 2was statistically significant. Results are expressed asmeans 6 1 SD.

560 Wilson et al. Communications-in-brief Vol. 71, No. 3, March 1999

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