The Role of NK Cells in the Autoimmune Thyroid Disease-associated Pregnancy Loss

Innate Immunity in Autoimmune Thyroid Disease during Pregnancy

Autoimmune thyroid disease (AITD) is the most common organ-specific autoimmune disorder clinically presented as Hashimoto thyroiditis (HT) and Graves' disease (GD). The pathogenesis of AITD is caused by an inappropriate immune response related to genetic, non-genetic, and environmental factors. Pregnancy is one of the factors that have a great influence on the function of the thyroid gland because of the increased metabolic demand and the effects of hormones related to pregnancy. During pregnancy, an adaptation of the maternal immune system occurs, especially of the innate immune system engaged in maintaining adaptive immunity in the tolerant state, preventing the rejection of the fetus. Pregnancy-related hormonal changes (estrogen, progesterone, hCG) may modulate the activity of innate immune cells, potentially worsening the course of AITD during pregnancy. This especially applies to NK cells, which are associated with exacerbation of HD and GD. On the other hand, previous thyroid disorders can affect fertility and cause adverse outcomes of pregnancy, such as placental abruption, spontaneous abortion, and premature delivery. Additionally, it can cause fetal growth retardation and may contribute to impaired neuropsychological development of the fetus. Therefore, maintaining the thyroid equilibrium in women of reproductive age and in pregnant women is of the highest importance.

Molecular and Cellular Insights: A Focus on Glycans and the HNK1 Epitope in Autism Spectrum Disorder

Autism Spectrum Disorder (ASD) is a synaptic disorder with a GABA/glutamate imbalance in the perineuronal nets and structural abnormalities such as increased dendritic spines and decreased long distance connections. Specific pregnancy disorders significantly increase the risk for an ASD phenotype such as preeclampsia, preterm birth, hypoxia phenomena, and spontaneous miscarriages. They are associated with defects in the glycosylation-immune placental processes implicated in neurogenesis. Some glycans epitopes expressed in the placenta, and specifically in the extra-villous trophoblast also have predominant functions in dendritic process and synapse function. Among these, the most important are CD57 or HNK1, CD22, CD24, CD33 and CD45. They modulate the innate immune cells at the maternal-fetal interface and they promote foeto-maternal tolerance. There are many glycan-based pathways of immunosuppression. N-glycosylation pathway dysregulation has been found to be associated with autoimmune-like phenotypes and maternal-autoantibody-related (MAR) autism have been found to be associated with central, systemic and peripheric autoimmune processes. Essential molecular pathways associated with the glycan-epitopes expression have been found to be specifically dysregulated in ASD, notably the Slit/Robo, Wnt, and mTOR/RAGE signaling pathways. These modifications have important effects on major transcriptional pathways with important genetic expression consequences. These modifications lead to defects in neuronal progenitors and in the nervous system's implementation specifically, with further molecular defects in the GABA/glutamate system. Glycosylation placental processes are crucial effectors for proper maternofetal immunity and endocrine/paracrine pathways formation. Glycans/ galectins expression regulate immunity and neurulation processes with a direct link with gene expression. These need to be clearly elucidated in ASD pathophysiology.

Anti-thyroid antibodies and underlying generalized immunologic aberrations in patients with reproductive failures

The link between autoimmune thyroid diseases and reproductive failures, including implantation failure and pregnancy loss, has been attracted a great deal of attention in the last two decades. In this regard, a considerable progress has been achieved in understanding the etiopathogenesis of the adverse pregnancy consequences related to the presence of anti-thyroid antibodies, however, the exact action mechanisms of these antibodies are not fully comprehended. Thyroid peroxidase antibodies (TPOAbs), thyroglobulin antibodies (TgAbs) and TSH receptor antibodies (TRAbs) are the anti-thyroid antibodies which are present in autoimmune thyroid disorder (AITD) patients, such as Hashimoto's thyroiditis. In this condition, the thyroid hormones production, which are essential for normal implantation and pregnancy, are disrupted, and compromise the embryo or fetus development. In addition, a hypothesis suggests that there is underlying generalized immune abnormalities behind the presence of these antibodies. On the other hand, similar immunologic aberrations have been observed in thyroid autoimmunity and reproductive complications, which are postulated to be the proper answer for the scientists who seek for the pathophysiology behind the presence of these antibodies. Elevated inflammatory responses and decreased immunoregulatory actions, seem to be the main interfering pathologic factors in maternal tolerance toward fetus. In addition, cross reactivity of these antibodies with antigenic determinants of egg, embryo and placenta is another suggested mechanism, causing implantation and pregnancy complications. The ability of anti-thyroid antibodies in passing through the placental barrier and affecting the fetal thyroid gland, makes them more threatening for maintenance of a pregnancy.

Endocrine Autoimmunity in Pregnancy

Human gestation leads to a number of physiological alterations which peak at the development of placentta known for, among many other functions, being a transient but highly potent endocrine organ. Hormonal activity of placenta is marked by its ability to continuously produce and secrete high levels of progesterone. Progesterone guards the well-being of the fetoplacental unit throughout the gestation and one of the proposed mechanisms of this principle involves the development of local and systemic immune tolerance mainly due to impediment of CD4+ lymphocyte activation. However, though these alterations are present and well-established, autoimmunity is not entirely rare and a wide spectrum of diseases can continue, or develop de novo, throughout the gestation or even after the delivery. Up-to-date data supports the existence of a relationship between the clinical course of chosen autoimmune diseases and levels of circulating sex steroids.

The most common autoimmune endocrinopathies in pregnant women are Hashimoto’s disease, Graves’ disease, and, more rarely, primary adrenal insufficiency in the form of Addison’s disease. Gestation can influence the clinical course of these endocrinopathies in patients who were diagnosed before conception. Multiple particles, like TSH-receptor stimulating antibodies, thyroid hormones, glucocorticoids, and anti-thyroid medications, can cross the placental barrier and evoke biological action in fetal tissues. Thyroid pathology in the form of postpartum thyroiditis is particularly prevalent in patients with positive anti-thyroperoxidase and anti-thyroglobulin antibodies. Certain populations are more at risk of developing numerous gestational complications and require regular follow-up. In our paper, we would like to address physiological, physiopathological, and clinical aspects of endocrine autoimmunity throughout human gestation, as well as special circumstances to consider in pregnant women.

Thyroid autoimmunity and its negative impact on female fertility and maternal pregnancy outcomes

Thyroid autoimmunity (TAI) is commonly defined as the presence of thyroperoxidase antibodies (TPOAbs) and/or thyroglobulin antibodies (TgAbs), which predisposes an individual to hypothyroidism. TAI affects nearly 10% of women of reproductive age and evokes great interest from clinicians because of its potentially negative impact on female fertility and pregnancy course. In this mini-review, we review the current literature concerning the influence of TPOAb or TPOAb/TgAb positivity without thyroid dysfunction on reproduction. TAI may negatively affect female fertility; several studies have found an increased prevalence of TAI in infertile women, especially in those with unexplained infertility and polycystic ovary syndrome. According to some observations, TAI might also be connected with premature ovarian insufficiency and endometriosis. The relationship between TAI and an increased risk of pregnancy loss is well documented. The pathophysiological background of these observations remains unclear, and researchers hypothesize on the direct infiltration of reproductive organs by thyroid antibodies, co-existence of TAI with other autoimmune diseases (either organ specific or systemic), immunological dysfunction leading to inhibition of immune tolerance, and relative thyroid hormone deficiency. Interestingly, in the current literature, better outcomes of assisted reproductive technology in women with TAI have been reported compared with those reported in earlier publications. One plausible explanation is the more widespread use of the intracytoplasmic sperm injection method. The results of randomized clinical trials have shown that levothyroxine supplementation is ineffective in preventing adverse pregnancy outcomes in women with TAI, and future research should probably be directed toward immunotherapy.

The Role of Cell and Gene Therapies in the Treatment of Infertility in Patients with Thyroid Autoimmunity

There is a rising incidence of infertility worldwide, and many couples experience difficulties conceiving nowadays. Thyroid autoimmunity (TAI) is recognized as one of the major female infertility causes related to a diminished ovarian reserve and potentially impaired oocyte maturation and embryo development, causing adverse pregnancy outcomes. Growing evidence has highlighted its impact on spontaneously achieved pregnancy and pregnancy achieved by in vitro fertilization. Despite the influence of thyroid hormones on the male reproductive system, there is insufficient data on the association between TAI and male infertility. In past years, significant progress has been achieved in cell and gene therapies as emerging treatment options for infertility. Cell therapies utilize living cells to restore healthy tissue microenvironment and homeostasis and usually involve platelet-rich plasma and various stem cells. Using stem cells as therapeutic agents has many advantages, including simple sampling, abundant sources, poor immunogenicity, and elimination of ethical concerns. Mesenchymal Stem Cells (MSCs) represent a heterogeneous fraction of self-renewal, multipotent non-hematopoietic stem cells that display profound immunomodulatory and immunosuppressive features and promising therapeutic effects. Infertility has a genetic component in about half of all cases, although most of its genetic causes are still unknown. Hence, it is essential to identify genes involved in meiosis, DNA repair, ovarian development, steroidogenesis, and folliculogenesis, as well as those involved in spermatogenesis in order to develop potential gene therapies for infertility. Despite advances in therapy approaches such as biological agents, autoimmune disorders remain impossible to cure. Recent research demonstrates the remarkable therapeutic effectiveness of MSCs in a wide array of autoimmune diseases. TAI is one of many autoimmune disorders that can benefit from the use of MSCs, which can be derived from bone marrow and adipose tissue. Cell and gene therapies hold great potential for treating autoimmune conditions, although further research is still needed.

Thyroid Autoimmunity in Adverse Fertility and Pregnancy Outcomes: Timing of Assisted Reproductive Technology in AITD Women

Thyroid autoimmunity (TAI) is prevalent in women of live-birthing age and has independently been associated with complications of fertility and pregnancy, in the case of spontaneous conception or after assisted reproductive technology (ART) treatment. However, it remains challenging to identify causation between infertility and TAI, even interventional trials looking at the impact of levothyroxine (LT4) treatment on fertility and pregnancy outcomes due to differences among study results which related to small scales, impropriate study designs, enrollment criteria of infertility cause and titer/hormone concentration measurements. Furthermore, many questions remain unsettled in ART management in AITD infertile women attempt pregnancy. Therefore, further observational and interventional trials are needed more comprehensive multiple-center, double blinded, and randomized.

Recent insights into the impact of immune dysfunction on reproduction in autoimmune thyroiditis

Autoimmune thyroiditis (AIT) is a common organ-specific autoimmune disease with a high incidence among women of childbearing age. Recent studies have reported that women with AIT are more susceptible to infertility, miscarriage and preterm birth. It has been investigated that abnormal changes in maternal immune system and maternal-fetal interface can dampen the immune tolerance between mother and fetus, which underlie the pathogenesis of adverse pregnancy outcomes. Hence, we summarize the immunological changes related to adverse reproductive outcomes in AIT and highlight the respective contributions of both humoral and cellular immune dysfunctions to pregnancy failures. Moreover, the direct impacts of AIT on maternal-fetal immune activation and biological influences to trophoblasts are discussed as well. All these associations require confirmation in larger studies, and the pathogenic mechanisms need to be better understood, which might provide useful information for clinical diagnosis and therapy of AIT.

The exploration of Hashimoto's Thyroiditis related miscarriage for better treatment modalities

Hashimoto's thyroiditis (HT) is the most prevalent autoimmune thyroid disease (ATD) worldwide and is strongly associated with miscarriage and even recurrent miscarriage (RM). Moreover, with a deepening understanding, emerging evidence has shown that immune dysfunctions caused by HT conditions, including imbalanced subsets of CD4+ T-helper cells, B regulatory (Breg) cells, high expression levels of CD56dim natural killer (NK) cells, and cytokines, possibly play an important role in impairing maternal tolerance to the fetus. In recent years, unprecedented progress has been made in recognizing the specific changes in immune cells and molecules in patients with HT, which will be helpful in exploring the mechanism of HT-related miscarriage. Based on these findings, research investigating some potentially more effective treatments, such as selenium (Se), vitamin D3, and intravenous immunoglobulin (IVIG), has been well developed over the past few years. In this review, we highlight some of the latest advances in the possible immunological pathogenesis of HT-related miscarriage and focus on the efficacies of treatments that have been widely introduced to clinical trials or practice described in the most recent literature.

Thyroxine replacement for subfertile women with euthyroid autoimmune thyroid disease or subclinical hypothyroidism

BACKGROUND

Thyroid disease is the second most common endocrine disorder affecting women of reproductive age. Subclinical hypothyroidism is diagnosed by an elevated thyroid-stimulating hormone concentration with a normal concentration of free thyroxine hormone. Autoimmune thyroid disease (ATD) is diagnosed by the presence of thyroid autoantibodies, regardless of thyroid hormone levels. Thyroxine may be a useful treatment for subfertile women with these two specific types of thyroid disease for improving pregnancy outcomes during assisted reproduction.

OBJECTIVES

To evaluate the efficacy and harms of levothyroxine replacement in subfertile women with subclinical hypothyroidism or with normal thyroid function and thyroid autoimmunity (euthyroid autoimmune thyroid disease, or euthyroid ATD) undergoing assisted reproduction.

SEARCH METHODS

We searched the Cochrane Gynaecology and Fertility (CGF) Group specialised register, CENTRAL, MEDLINE, Embase, PsycINFO, CINAHL and two trials registers together with reference checking and contact with study authors and experts in the field to identify studies. We searched for all published and unpublished randomised controlled trials (RCTs) comparing thyroxine with no treatment or placebo, without language restrictions, from inception to 8 April 2019, and in consultation with the Cochrane CGF Information Specialist.

SELECTION CRITERIA

We included women undergoing assisted reproduction treatment, meaning both in vitro fertilisation and intracytoplasmic sperm injection, with a history of subfertility and with subclinical hypothyroidism or with euthyroid ATD. We excluded women with a previously known clinical hypothyroidism or already taking thyroxine or tri-iodothyronine. RCTs compared thyroxine (levothyroxine) with either placebo or no treatment.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane. Our primary review outcomes were live birth and adverse events of thyroxine; our secondary outcomes were clinical pregnancy, multiple pregnancy and miscarriage.

MAIN RESULTS

The review included four studies with 820 women. The included studies were of overall low risk of bias. Using GRADE methodology, we assessed the quality of evidence for the primary outcomes of this review to be very low- to low-quality evidence. Evidence was downgraded for imprecision as it was based on single, small trials with wide confidence intervals (CI). We were able to include data from three of the four included studies.In one study of women with both subclinical hypothyroidism and positive or negative anti-TPO antibodies (autoimmune disease), the evidence suggested that thyroxine replacement may have improved live birth rate (RR 2.13, 95% CI 1.07 to 4.21; 1 RCT, n = 64; low-quality evidence) and it may have led to similar miscarriage rates (RR 0.11, 95% CI 0.01 to 1.98; 1 RCT, n = 64; low-quality evidence). The evidence suggested that women with both subclinical hypothyroidism and positive or negative anti-TPO antibodies would have a 25% chance of a live birth with placebo or no treatment, and that the chance of a live birth in these women using thyroxine would be between 27% and 100%.In women with normal thyroid function and thyroid autoimmunity (euthyroid ATD), treatment with thyroxine replacement compared with placebo or no treatment may have led to similar live birth rates (risk ratio (RR) 1.04, 95% CI 0.83 to 1.29; 2 RCTs, number of participants (n) = 686; I2 = 46%; low-quality evidence) and miscarriage rates (RR 0.83, 95% CI 0.47 to 1.46, 2 RCTs, n = 686, I2 = 0%; low-quality evidence). The evidence suggested that women with normal thyroid function and thyroid autoimmunity would have a 31% chance of a live birth with placebo or no treatment, and that the chance of a live birth in these women using thyroxine would be between 26% and 40%.Adverse events were rarely reported. One RCT reported 0/32 in the thyroxine replacement group and 1/32 preterm births in the control group in women diagnosed with subclinical hypothyroidism and positive or negative anti-TPO antibodies. One RCT reported 21/300 preterm births in the thyroxine replacement group and 19/300 preterm births in the control group in women diagnosed with positive anti-TPO antibodies. None of the RCTs reported on other maternal pregnancy complications, foetal complications or adverse effects of thyroxine.

AUTHORS' CONCLUSIONS

We could draw no clear conclusions in this systematic review due to the very low to low quality of the evidence reported.

Does severe vitamin D deficiency impact obstetric outcomes in pregnant women with thyroid autoimmunity?

Purpose: Vitamin D plays an important role in the modulation of the immune system and anti-autoimmune activities. Autoimmune thyroid diseases related to endocrine disorders are associated with poor obstetric outcomes in pregnancy. Herein, we aimed to investigate the contribution of vitamin D hypovitaminosis to poor pregnancy outcomes in pregnant women with the positive autoimmune antibody.Materials and methods: This was a prospective case-control study that enrolled pregnant women at their first trimester. The pregnant women were divided based on thyroid antibody (TA) status (TA-positive pregnant group (TAs (+)) and negative group (TAs (-)). Vitamin D status was categorized as sufficient, insufficient, and deficient (severe and moderate).Results: A total of 283 pregnant women were enrolled in this study. A total of 219 pregnant women were assigned to the TAs (-) group and 64 to the TAs (+) group. The rate of vitamin D insufficiency was 8.7, and 7.8% in the pregnant with TAs (-), and the pregnant with TAs (+) groups, respectively. Vitamin D deficiency was highly prevalent in all groups. Specifically, the prevalence rate was 91 and 92% in the pregnant with TAs (-) and the pregnant with TAs (+) groups, respectively. Admission to the neonatal intensive care unit (NICU) was more prevalent in the pregnant with TAs (+) group than in the pregnant with TAs (-) group (40.6 versus 25%; p = .0187; effect size (ES) = 0.134). The rate of gestational diabetes mellitus (GDM) was significantly higher in the pregnant women with TAs (+) group than that in the pregnant women with TAs (-) group (12.5 versus 4.1%; p = .03; ES =0.13). The rate of NICU admission and GDM was significantly higher in the severe vitamin D-deficient pregnant group with TAs (+) than that in the severe vitamin D-deficient pregnant group with TAs (-) (47 versus 23%; p = .007; ES =0.207 and 19.4% versus 4.1%; p = .006; ES =0.214, respectively).Conclusions: Severe vitamin D deficiency may contribute to increase the prevalence of GDM and need for NICU admission in pregnant women with positive TA.

Autoimmune thyroid disease during pregnancy

Understanding of changes in thyroid function and the consequences of thyroid disease during pregnancy has rapidly grown in the past two decades, and revised American Thyroid Association guidelines on this topic were published in 2017. This Review explores the association between thyroid autoimmunity and complications during and after pregnancy. Thyroid autoimmunity refers to the presence of antibodies to thyroperoxidase or thyroglobulin, or thyroid-stimulating hormone receptor antibodies (TRAbs), or a combination of these, and is present in up to 18% of pregnant women. Thyroid antibodies in pregnant women with normal functioning thyroids (ie, euthyroid) have been associated with several complications, including miscarriage and premature delivery. Treatments to improve pregnancy outcomes are being studied. Whether thyroid antibodies are associated with infertility and assisted reproductive technology outcomes is unclear; although, treatment with low doses of levothyroxine, which is usually used to treat hypothyroidism, can be considered in such situations. Additionally, thyroid antibodies have been associated with other neonatal and maternal complications. All these associations require confirmation in larger prospective studies, and their pathogenic mechanisms need to be better understood. Post-partum thyroiditis is substantially more frequent in women who have thyroid antibodies during pregnancy than in those who do not have thyroid antibodies; however, whether treatment can prevent post-partum thyroiditis in women who are or have been antibody positive is unknown. Finally, TRAbs cross the placenta from the mother to the fetus and can cause fetal or neonatal hyperthyroidism. Therefore, women who are positive for TRAbs during pregnancy should be monitored.

Innate Immune System at the Maternal-Fetal Interface: Mechanisms of Disease and Targets of Therapy in Pregnancy Syndromes

The maternal-fetal interface is an immunologically unique site that allows the tolerance to the allogenic fetus and maintains host defense against possible pathogens. Balanced immune responses are required for the maintenance of successful pregnancy. It has been demonstrated that innate immune disturbances may be responsible for some adverse pregnancy outcomes such as preeclampsia (PE); hemolysis, elevated liver enzymes, low platelets (HELLP) syndrome; intrauterine growth restriction (IUGR); and recurrent spontaneous abortion (RSA). Observational studies suggest that immunomodulatory treatments in pregnancy-specific complications may improve both the hematological/biochemical features in the mother and the perinatal outcomes. The following review will discuss how recent and relevant findings in the field of the innate immunity have advanced our understanding of the role of inflammation and innate immune system in the pathogenesis of pregnancy failure and will discuss the therapeutic outcomes of the existing studies and clinical trials in light of these new insights.

Peripheral blood natural killer cells and mild thyroid abnormalities in women with reproductive failure

Abnormalities in peripheral blood natural killer (NK) cells have been reported in women with primary infertility and recurrent spontaneous abortion (RSA) and several studies have been presented to define cutoff values for abnormal peripheral blood NK cell levels in this context. Elevated levels of NK cells were observed in infertile/RSA women in the presence of thyroid autoimmunity (TAI), while no studies have been carried out, to date, on NK cells in infertile/RSA women with non-autoimmune thyroid diseases. The contribution of this study is two-fold: (1) the evaluation of peripheral blood NK cell levels in a cohort of infertile/RSA women, in order to confirm related data from the literature; and (2) the assessment of NK cell levels in the presence of both TAI and subclinical hypothyroidism (SCH) in order to explore the possibility that the association between NK cells and thyroid function is not only restricted to TAI but also to SCH. In a retrospective study, 259 age-matched women (primary infertility [n = 49], primary RSA [n = 145], and secondary RSA [n = 65]) were evaluated for CD56+CD16+NK cells by flow cytometry. Women were stratified according to thyroid status: TAI, SCH, and without thyroid diseases (ET). Fertile women (n = 45) were used as controls. Infertile/RSA women showed higher mean NK cell levels than controls. The cutoff value determining the abnormal NK cell levels resulted ⩾15% in all the groups of women. Among the infertile/RSA women, SCH resulted the most frequently associated thyroid disorder while no difference resulted in the prevalence of TAI and ET women between patients and controls. A higher prevalence of women with NK cell levels ⩾15% was observed in infertile/RSA women with SCH when compared to TAI/ET women. According to our data, NK cell assessment could be used as a diagnostic tool in women with reproductive failure and we suggest that the possible association between NK cell levels and thyroid function can be described not only in the presence of TAI but also in the presence of non-autoimmune thyroid disorders.

Molecular basis of thyrotropin and thyroid hormone action during implantation and early development

BACKGROUND

Implantation and early embryo development are finely regulated processes in which several molecules are involved. Evidence that thyroid hormones (TH: T4 and T3) might be part of this machinery is emerging. An increased demand for TH occurs during gestation, and any alteration in maternal thyroid physiology has significant implications for both maternal and fetal health. Not only overt but also subclinical hypothyroidism is associated with infertility as well as with obstetric complications, including disruptions and disorders of pregnancy, labor, delivery, and troubles in early neonatal life.

METHODS

We searched the PubMed and Google Scholar databases for articles related to TH action on ovary, endometrium, trophoblast maturation and embryo implantation. In addition, articles on the regulation of TH activity at cellular level have been reviewed. The findings are hereby summarized and critically discussed.

RESULTS

TH have been shown to influence endometrial, ovarian and placental physiology. TH receptors (TR) and thyrotropin (thyroid-stimulating hormone: TSH) receptors (TSHR) are widely expressed in the feto-maternal unit during implantation, and both the endometrium and the trophoblast might be influenced by TH either directly or through TH effects on the synthesis and activity of implantation-mediating molecules. Interestingly, due to the multiplicity of mechanisms involved in TH action (e.g. differential expression of TR isoforms, heterodimeric receptor partners, interacting cellular proteins, and regulating enzymes), the TH concentration in blood is not always predictive of their cellular availability and activity at both genomic and nongenomic level.

CONCLUSIONS

In addition to the known role of TH on the hormonal milieu of the ovarian follicle cycle, which is essential for a woman's fertility, evidence is emerging on the importance of TH signaling during implantation and early pregnancy. Based on recent observations, a local action of TH on female reproductive organs and the embryo during implantation appears to be crucial for a successful pregnancy. Furthermore, an imbalance in the spatio-temporal expression of factors involved in TH activity might induce early arrest of pregnancy in women considered as euthyroid, based on their hormonal blood concentration. In conclusion, alterations of the highly regulated local activity of TH may play a crucial, previously underestimated, role in early pregnancy and pregnancy loss. Further studies elucidating this topic should be encouraged.

Thyroid autoantibodies in pregnancy: their role, regulation and clinical relevance

Autoantibodies to thyroglobulin and thyroid peroxidase are common in the euthyroid population and are considered secondary responses and indicative of thyroid inflammation. By contrast, autoantibodies to the TSH receptor are unique to patients with Graves' disease and to some patients with Hashimoto's thyroiditis. Both types of thyroid antibodies are useful clinical markers of autoimmune thyroid disease and are profoundly influenced by the immune suppression of pregnancy and the resulting loss of such suppression in the postpartum period. Here, we review these three types of thyroid antibodies and their antigens and how they relate to pregnancy itself, obstetric and neonatal outcomes, and the postpartum.

Pathogenesis of infertility and recurrent pregnancy loss in thyroid autoimmunity

Thyroid autoimmunity is the most prevalent autoimmune state that affects up to 4% of women during the age of fertility. A growing body of clinical studies links thyroid autoimmunity as a cause of infertility and adverse pregnancy outcomes that includes miscarriage or preterm deliveries. Importantly, these adverse effects are persistent in euthyroid women. In the current review we elaborate on the pathogenesis that underlies infertility and increased pregnancy loss among women with autoimmune thyroid disease. Such mechanisms include thyroid autoantibodies that exert their effect in a TSH-dependent but also in a TSH-independent manner. The later includes quantitative and qualitative changes in the profile of endometrial T cells with reduced secretion of IL-4 and IL-10 along with hypersecretion of interferon-γ. Polyclonal B cells activation is 2-3 time more frequent in thyroid autoimmunity and is associated with increased titers of non-organ specific autoantibodies. Hyperactivity and Increased migration of cytotoxic natural killer cells that alter the immune and hormonal response of the uterus is up to 40% more common in women with thyroid autoimmunity. Lack of vitamin D was suggested as a predisposing factor to autoimmune diseases, and was shown to be reduced in patients with thyroid autoimmunity. In turn, its deficiency is also linked to infertility and pregnancy loss, suggesting a potential interplay with thyroid autoimmunity in the context of infertility. In addition, thyroid autoantibodies were also suggested to alter fertility by targeting zona pellucida, human chorionic gonadotropin receptors and other placental antigens.

Management of hypothyroidism in pregnancy

PURPOSE OF REVIEW

Examine recent studies on the assessment of thyroid status in pregnancy, approach to thyroid testing, the spectrum of hypothyroidism in pregnancy, and strategies for thyroid replacement in women with known hypothyroidism.

RECENT FINDINGS

Trimester-specific references range for thyroid-stimulating hormone (TSH) and free thyroxine in pregnancy must take into account iodine and thyroid autoantibody status, race, BMI, as well as other factors. Thyroid testing of only those pregnant women at increased risk for thyroid disease, case finding, will miss 30-80% of women with thyroid disease. Subclinical hypothyroidism is associated with an increasing number of adverse effects including infertility, miscarriage, preterm delivery, and breech presentation at birth. Many pregnant women with known hypothyroidism have an out-of-range TSH at the time of confirmed pregnancy. A variety of strategies are effective at keeping serum TSH normal during pregnancy including preconception increase in thyroxine, increase in thyroxine dose at the time pregnancy is confirmed, or making adjustments based on serum TSH monitoring.

SUMMARY

Evaluation of thyroid status in pregnancy requires an understanding of pregnancy-associated changes in thyroid function tests and how they vary by trimester. The spectrum of hypothyroidism in pregnancy includes isolated thyroid peroxidase antibody positivity, isolated hypothyroxinemia, subclinical and overt hypothyroidism. These patterns, in some situations, may be related to iodine status, selenium status, or underlying thyroid disease. There are a variety of approaches to management of thyroxine replacement in known hypothyroid women at the time of pregnancy that are all effective at maintaining a normal range during pregnancy.

Reproductive immunology: current status and future directions (part I)

Extensive research work over the past couple of decades has indicated a series of intricate relations between immune and reproductive systems. A range of reproductive immunology topics including the roles of adoptive and innate immunity in infertility and pregnancy, the immune system's role in induction of labor and preterm delivery, and immuno-modulatory effects of the female sex hormones will be discussed in this and the next issue of the Journal. The implications of this research on the development of novel therapeutic approaches are also addressed.