Women with Recurrent Miscarriage Have Decreased Expression of 25-Hydroxyvitamin D3-1α-Hydroxylase by the Fetal-Maternal Interface

No evidence of a causal relationship between miscarriage and 25-hydroxyvitamin D: a Mendelian randomization study

STUDY QUESTION

Is there a causal relationship between 25-hydroxyvitamin D (25OHD) and miscarriage?

SUMMARY ANSWER

In this study, little evidence of a causal relationship was found between low serum 25OHD concentration or vitamin D deficiency and the risk of miscarriages.

WHAT IS KNOWN ALREADY

Associations between low vitamin D levels and increased risk of miscarriage have been reported, but causality is unclear.

STUDY DESIGN SIZE DURATION

The latest and largest genome-wide association studies (GWAS) for serum 25OHD concentration (n = 417 580), vitamin D deficiency (426 cases and 354 812 controls), miscarriage (16 906 cases and 149 622 controls), and the number of miscarriages (n = 78 700) were used to explore the causal association between serum vitamin D levels and miscarriage by two-sample Mendelian randomization analysis.

PARTICIPANTS/MATERIALS SETTING METHODS

This study was based on summary GWAS results from the FinnGen database and the UK Biobank. The random-effect inverse-variance weighted method was regarded as the primary analysis; MR-Egger, weighted median, weighted mode, simple mode, and MR-pleiotropy residual sum and outlier (MR-PRESSO) were further employed as complementary methods. MR-Egger intercept analysis and MR-PRESSO were employed to test pleiotropy, and Cochran's Q statistic and leave-one-out sensitivity analysis were used to determine the heterogeneity and robustness of the overall estimates, respectively.

MAIN RESULTS AND THE ROLE OF CHANCE

There was insufficient evidence of causal associations between serum 25OHD concentration and miscarriage (odds ratio (OR) = 0.995, 95% CI: 0.888 to 1.114, P = 0.927), or the number of miscarriages (β = -0.004, 95% CI: -0.040 to 0.032, P = 0.829). Furthermore, little evidence of causality between genetically determined vitamin D deficiency to miscarriage (OR = 0.993, 95% CI: 0.966 to 1.021, P = 0.624), or the number of miscarriages (β = 0.001, 95% CI: -0.009 to 0.011, P = 0.828), was observed. The results of the sensitivity analysis were robust, and no significant heterogeneity or horizontal pleiotropy was found.

LIMITATIONS REASONS FOR CAUTION

This study is limited by the absence of female-specific GWAS data and the limited amount of GWAS data available for this study, as well as the need for caution in generalizing the findings to non-European ethnic groups.

WIDER IMPLICATIONS OF THE FINDINGS

These findings enhance the current understanding of the intricate association between vitamin D and pregnancy outcomes, challenging prevailing beliefs regarding the strong association with miscarriage. The results provide a special perspective that may prompt further exploration and potentially offer insights for guiding future research and informing clinical guidelines pertaining to the management of miscarriage.

STUDY FUNDING/COMPETING INTERESTS

This project was supported by the Hubei Provincial Natural Science Foundation Program General Surface Project (2022CFB200), the Key Research & Developmental Program of of Hubei Province (2022BCA042), the Fundamental Research Funds for the Central Universities (2042022gf0007, 2042022kf1210), and the Interdisciplinary Innovative Talents Foundation from Renmin Hospital of Wuhan University (JCRCWL-2022-001, JCRCYG-2022-009). All authors have no conflicts of interest to declare.

TRIAL REGISTRATION NUMBER

N/A.

CPY27B1-related vitamin D deficiency contributes to the impaired function of CD4+T cells in Recurrent spontaneous miscarriage

The study aimed to explore the relationship between the expression of cytochrome P450 family 27 subfamily B member 1 (CYP27B1), vitamin D, and impaired T cell subsets in recurrent spontaneous miscarriage (RSM). A Total of 779 healthy women of childbearing age and 1031 women with a history of RSM were involved in this study. The results of flow cytometry showed that the proportion of Tregs was higher in healthy women than in the women with RSM. For cytokines, the levels of interleukin-17 (IL-17) and interferon-gamma (IFN-γ) were significantly higher in RSM patients than in healthy women, while IL-10 was notably lower in RSM patients. Furthermore, compared to healthy individuals, RSM patients had lower levels of serum 25(OH)D detected by chemiluminescence. The frequency of Tregs was negatively correlated with 25(OH)D. Specifically, for every 10 ng/ml increase in 25(OH)D, the percentage of Tregs increased by 0.58 as calculated. IL-17 and IFN-γ were inversely correlated with 25(OH)D, while the serum interleukin-10 (IL-10) level was positively correlated with 25(OH)D. CYP27B1 was found to be expressed in both cytotrophoblast and extracellular villi trophoblast cells. However, reduced expression of CYP27B1 was observed in the placenta with RSM. Notably, the level of 25(OH)D increased in the supernatant of CYP27B1 knockdown BeWo compared to normal cells, while human chorionic gonadotropin (hCG) was significantly reduced. The hCG secretion of CYP27B1 KO BeWo cells was partially restored after 1,25(OH)2D3 supplementation. In addition, 1,25(OH)2D3 treatment could induce more CD4+ T cells to convert to Foxp3+iTreg, which in turn inhibited the secretion of IL-17, IFN-γ. In summary, this research unveiled a connection between reduced CYP27B1 and vitamin D deficiency in RSM. Our study underscores the potential benefits of vitamin D treatment supplementation in the context of RSM. However, it is important to note that further research is imperative to validate these observations.

Altered vitamin D metabolism is involved in the dysregulation of γδT cell function and their crosstalk with trophoblasts in recurrent pregnancy loss

BACKGROUND

Recurrent pregnancy loss (RPL) is a common disease characterized by immune dysfunction and vitamin D deficiency. This study aimed to investigate vitamin D metabolism and γδT cell phenotypes at the maternal-fetal interface in women with early normal pregnancy (NP) and RPL and to determine the effects of vitamin D on the functions of γδT cells and their crosstalk with trophoblasts.

METHODS

The levels of 25-(OH)VD₃ , the expression of vitamin D metabolic enzymes in the villi, and the proportion of γδT cells in the decidua were detected in women with NP and RPL. After treatment with different concentrations of vitamin D, the mRNA expression of the vitamin D receptor (VDR), cytokines, and transcription factors was detected in Vδ2⁺ γδT cells. In addition, the proliferation, migration, and invasion of HTR-8/SVneo trophoblasts were determined by co-culturing them with vitamin D-treated Vδ2⁺ γδT cells and their supernatants.

RESULTS

In women with RPL, the level of 25-(OH)VD₃ in the villi was increased; however, that of CYP27B1 (enzyme converting 25-(OH)VD₃ into 1,25-(OH)₂ VD₃ ) was decreased. In addition, the proportion of Vδ2⁺ γδT cells increased, whereas that of Foxp3⁺ Vδ2⁺ γδT cells decreased in the decidua of women with RPL. An in vitro study showed that vitamin D increased the expression of VDR mRNA and Foxp3, but decreased the expression of IFN-γ mRNA, in Vδ2⁺ γδT cells. Finally, vitamin D-treated Vδ2⁺ γδT cells promoted trophoblast migration and invasion.

CONCLUSIONS

Abnormal vitamin D metabolism and γδT cell proportions were present at the maternal-fetal interface in women with RPL. Under normal pregnancy conditions, vitamin D can induce the differentiation of decidual Vδ2⁺ γδT cells toward an anti-inflammatory phenotype (Treg-like γδT cells) and modulate the crosstalk between Vδ2⁺ γδT cells and trophoblasts. This article is protected by copyright. All rights reserved.

Glucose/insulin metabolism and vitamin D in women with recurrent pregnancy loss

OBJECTIVE

Glucose/insulin metabolism has been related to recurrent pregnancy loss (RPL) through mechanisms not really clarified. Also, vitamin D deficiency seems to be associated to RPL. The purpose of our study was to evaluate the correlation between glucose/insulin metabolism parameters and vitamin D levels in women with history of RPL.

STUDY DESIGN

Observational retrospective study on RPL women. The correlation among vitamin D levels and fasting glucose (FG), fasting insulin (FI), Homeostatic model assessment of insulin resistance (HOMA-IR) index, area under glucose curve (AUC-Glyc) and area under insulin curve (AUC-Ins), was evaluated.

RESULTS

One-hundred and twenty-seven RPL women were classified into three subgroups (0-1-2) according to the levels of FI. We found a statistically significant linear Pearson correlation between FI and HOMA-IR (r = .840; P = .001). An, inverse, but non-significant correlation both between vitamin D and FI (R = -.202, ns) and vitamin D levels and AUC-Ins (R = -.288, ns) was observed. The variables vitamin D, HOMA-IR and AUC-Ins were statistically significant in the considered subgroups (Vitamin D: ANOVA + Bonferroni test: 0 vs. 1; P = .001; 0 vs. 2; P = .010; 1 vs. 2; P = .657; HOMA-IR: ANOVA + Bonferroni test: 0 vs. 1; P = .014; 0 vs. 2; P = .001; 1 vs. 2; P = .001; AUC-Ins: ANOVA + Bonferroni test: 0 vs. 1; P = .010; 0 vs. 2; P = .206; 1 vs. 2; P = .980).

CONCLUSIONS

Vitamin D might play additional roles in the pathogenesis of RPL, beyond its well known immunomodulatory role.

Vitamin D receptor gene polymorphisms and haplotypes in the etiology of recurrent miscarriages

A few years ago it was shown that disturbed metabolism of the vitamin D/receptor (VD/VDR) complex may be important in the etiology of spontaneous abortion, as well as in the etiology of recurrent miscarriages (RM). The goal of this study was to investigate the association between four maternal VDR polymorphisms as well as haplotypes settings and RM occurrence in a Polish population of women in reproductive age. A total of 230 women were recruited to this study (110 with RM, 120 consecutively recruited age-matched healthy women with at least two full-term pregnancies and with no history of miscarriages). DNA samples were genotyped for VDR polymorphisms: FokI (rs2228570), BsmI (rs1544410), ApaI (rs7975232) and TaqI (rs731236). Significant differences in genotype distributions and allele frequencies between case and control groups were observed in VDR BsmI polymorphism (GG vs. GA and AA, OR = 0.56, p = 0.036 and OR = 1.49, p = 0.035, respectively). The best evidence of an association with RM prevention was observed for the TTGT haplotype, which was more frequent among controls than cases even after permutation test (0.09 vs. 0.017, p = 0.0024). Other haplotypes were also significantly more frequent in the control group: TGT (rs7975232, rs1544410, rs2228570), TG (rs7975232, rs1544410), TTG (rs731236, rs7975232, rs1544410), TT (rs731236, rs7975232). Our research indicated the possible role of VDR BsmI genetic polymorphism in RM etiology, suggesting at the same time the active role of maternal VD metabolism and its influence on pregnancy outcome. The significant influence of several maternal haplotypes was shown to prevent RM occurrence.

SNP rs12794714 of CYP2R1 is associated with serum vitamin D levels and recurrent spontaneous abortion (RSA): a case-control study

PURPOSE

Vitamin D (VD) deficiency seems to be associated with the risk of recurrent spontaneous abortion (RSA). Vitamin D receptor (VDR) and cytochrome P450 family 2 subfamily R member 1 (CYP2R1) are two genes which are vital for VD metabolism and actions. However, whether single-nucleotide polymorphisms (SNPs) in these genes are correlated with the risk of RSA are poorly understood. Therefore, we aimed to characterize the relationships among VDR SNPs, CYP2R1 SNPs and RSA.

METHODS

This case-control study enrolled 75 RSA patients and 83 controls. Serum VD and some cytokines were detected with LC-MS/MS and flow cytometry, respectively. Genotyping for three SNPs of CYP2R1 (rs10741657, rs10766197 and rs12794714) and five SNPs of VDR (rs7975232, rs1544410, rs2189480, rs2228570 and rs2239179) was done with polymerase chain reaction (PCR) and high-throughput sequencing. All the data were analyzed with appropriate methods and in different models.

RESULTS

The results revealed a significant correlation between the AG genotype of CYP2R1 rs12794714 and VD levels (OR 0.686; 95% CI 0.49-0.96; p = 0.028). Besides, the AG and GG genotypes of CYP2R1 rs12794714 were markedly related to the risk of RSA (OR 52.394, 59.497; 95% CI 2.683-1023.265, 3.110-1138.367; p = 0.009, 0.007, respectively).

CONCLUSION

Our results indicate that CYP2R1 rs12794714 might be a risk factor for RSA. Hence, early screening of pregnant women for CYP2R1 rs12794714 is necessary to warrant proactive counseling and treatment against RSA.

Regulatory T Cells in Pregnancy: It Is Not All About FoxP3

In pregnancy, the semi-allogeneic fetus needs to be tolerated by the mother's immune system. Regulatory T cells (Tregs) play a prominent role in this process. Novel technologies allow for in-depth phenotyping of previously unidentified immune cell subsets, which has resulted in the appreciation of a vast heterogeneity of Treg subsets. Similar to other immunological events, there appears to be great diversity within the Treg population during pregnancy, both at the maternal-fetal interface as in the peripheral blood. Different Treg subsets have distinct phenotypes and various ways of functioning. Furthermore, the frequency of individual Treg subsets varies throughout gestation and is altered in aberrant pregnancies. This suggests that distinct Treg subsets play a role at different time points of gestation and that their role in maintaining healthy pregnancy is crucial, as reflected for instance by their reduced frequency in women with recurrent pregnancy loss. Since pregnancy is essential for the existence of mankind, multiple immune regulatory mechanisms and cell types are likely at play to assure successful pregnancy. Therefore, it is important to understand the complete microenvironment of the decidua, preferably in the context of the whole immune cell repertoire of the pregnant woman. So far, most studies have focused on a single mechanism or cell type, which often is the FoxP3 positive regulatory T cell when studying immune regulation. In this review, we instead focus on the contribution of FoxP3 negative Treg subsets to the decidual microenvironment and their possible role in pregnancy complications. Their phenotype, function, and effect in pregnancy are discussed.

Vitamin D Effects on the Immune System from Periconception through Pregnancy

Vitamin D is a well-known secosteroid and guardian of bone health and calcium homeostasis. Studies on its role in immunomodulatory functions have expanded its field in recent years. In addition to its impact on human physiology, vitamin D influences the differentiation and proliferation of immune system modulators, interleukin expression and antimicrobial responses. Furthermore, it has been shown that vitamin D is synthesized in female reproductive tissues and, by modulating the immune system, affects the periconception period and reproductive outcomes. B cells, T cells, macrophages and dendritic cells can all synthesize active vitamin D and are involved in processes which occur from fertilization, implantation and maintenance of pregnancy. Components of vitamin D synthesis are expressed in the ovary, decidua, endometrium and placenta. An inadequate vitamin D level has been associated with recurrent implantation failure and pregnancy loss and is associated with pregnancy-related disorders like preeclampsia. This paper reviews the most important data on immunomodulatory vitamin D effects in relation to the immune system from periconception to pregnancy and provides an insight into the possible consequences of vitamin D deficiency before and during pregnancy.

Vitamin D Receptor Polymorphisms Associated with Autism Spectrum Disorder

Vitamin D is endowed with a number of biological properties, including down-regulation of inflammation, and might contribute to the pathogenesis of autism spectrum disorders (ASD). Vitamin D binds to the vitamin D Receptor (VDR); the biological activity of the ensuing complex depends on VDR FokI, BsmI, ApaI, and TaqI gene polymorphisms. We evaluated such Single Nucletoide Polymorphismsm (SNPs) in a cohort of 100 Italian families with ASD children. FokI genotype distribution was skewed in ASD children compared with their healthy sibs (P_c = 0.03 2 df) and to a group of 170 Italian healthy women (HC) (P_c = 0.04 2 df). FokI genotype and allelic distribution skewing were also observed in mothers of ASD children compared to HC (P_c = 0.04 2 df). Both Transmission Disequilibrium Test for single loci and haplotype analysis distribution revealed a major FokI (C) allele-mediated protective effect, which was more frequently transmitted (73%) than not transmitted to healthy sibs (P = 0.02). A protective FokI-, BsmI-, ApaI-, and TaqI (CCAG) haplotype was more frequently carried by healthy sibs than by ASD children (P = 1 × 10^-4 ; OR: 0.1, 95% CI: 0.03-0.4) too. Finally, a strong gene-dose association of FokI (T) allele with both higher Childhood Autism Rating Scale score (P_c = 0.01) and, particularly, with hyperactivity behavior (P_c = 0.006) emerged in ASD children. Because the protein produced by the FokI (T) allele is transcriptionally less active than that produced by the FokI (C) allele, the reduced biological activity of the vitamin D/VDR complex prevalent in ASD could favor ASD- and maternal immune activation- associated inflammation. Vitamin D supplementation might be useful in preventative and rehabilitation protocols for ASD. Autism Res 2020, 13: 680-690. © 2020 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: Vitamin D deficiency and Vitamin D receptor (VDR) polymorphisms are associated with structural and functional brain abnormalities and behavioral disorders. We analyzed the association of VDR gene polymorphisms in a cohort of 100 Italian families with ASD children. A strong correlation between one of the VDR polymorphisms and hyperactivity behavior was evidenced in ASD children. In healthy mothers, the same VDR polymorphism was also correlated with an increased risk of giving birth to children with ASD.

Altered decidual and placental catabolism of vitamin D may contribute to the aetiology of spontaneous miscarriage

INTRODUCTION

Vitamin D catabolizing enzymes, along with vitamin D receptor (VDR) and vitamin D binding protein (DBP) are expressed in the decidua and placenta during pregnancy and capable of synthesizing active vitamin D. Vitamin D plays roles in immunoregulation and trophoblast invasion, key features of a successful pregnancy. Epidemiological data suggests that vitamin D deficiency is associated with both spontaneous and recurrent miscarriage but few studies have investigated the expression of the key vitamin D catabolizing enzymes in miscarriage.

METHODS

Placenta and decidua were collected after termination of apparently normal pregnancies (controls, n = 22) or spontaneous miscarriage (n = 20). Immunohistochemical staining, Western Blot and qRT-PCR were performed for CYP27B1, CYP24A1, CYP2R1, VDR and DBP (not qRT-PCR). HTR-8/SVneo cells were cultured in CoCL₂ (hypoxic mimetic) or LPS (bacterial infection mimetic) for 24 h, RNA extracted and qRT-PCR performed for CYP27B1, CYP24A1, CYP2R1 and VDR.

RESULTS

In spontaneous miscarriage, placental and decidual expression of CYP27B1 was reduced, while expression of CYP24A1, VDR and DBP was increased. When a trophoblast cell line was treated with CoCL₂ expression of CYP27B1 was increased and CYP24A1 was reduced, while LPS induced expression of VDR.

DISCUSSION

This is the first report of altered utero-placental vitamin D catabolism in spontaneous miscarriage. It is becoming accepted that women who are undergoing assisted reproductive technologies should ensure they have sufficient vitamin D levels prior to pregnancy, these data support that all women should ensure they are vitamin D replete before planning to get pregnant.

Endocrine causes of recurrent pregnancy loss

OBJECTIVE

To review the available data on endocrine disorders and recurrent pregnancy loss.

FINDINGS

Our group found that most endocrine disorders do not seem to be correlated with a diagnosis of recurrent pregnancy loss (RPL). The exception to this is testing for thyroid stimulating hormone and thyroid antibodies, which is recommended due to a strong correlation with recurrent pregnancy loss and positive anti-thyroid peroxidase antibodies.

CONCLUSION

The available literature supports testing thyroid function and antibodies in women with RPL. Testing for other endocrine disorders is only warranted if otherwise clinically indicated, independent from a history of recurrent pregnancy loss.

Recurrent pregnancy loss and vitamin D: A review of the literature

Recurrent pregnancy loss (RPL) affects approximately 1%-2% of reproductive women. Auto- and cellular immune responses seem to be associated with RPL. Vitamin D (VD) has been shown to play a role in the modulation of the immune system. Effects of VD deficiency (VDD) in pregnancy have been associated with preeclampsia, gestational diabetes, fetal growth restriction, preterm labor, and sporadic spontaneous abortion (SA). We systematically reviewed articles that studied women with 2 or more SA and its association with VD. Eleven studies were included. Studies reported a high prevalence of VD insufficiency (VDI) or VDD in women with RPL and suggested that this could be associated with immunological dysregulation and consequently with RPL. Immunological benefits were reported in the peripheral blood of women with RPL after VD exposure. Thus, it is possible to speculate a beneficial role for VD supplementation in RPL. It seems that there are not differences in the vitamin D receptor (VDR) and CYP27B1 expression in endometrium of women with RPL but, in villous and decidual tissues, RPL women seem to have a decreased expression of VDR and, perhaps, a decreased expression of CYP27B1. Further randomized controlled studies are required to investigate the association between VDD or VDI and RPL.

Vitamin D, autoimmunity and recurrent pregnancy loss: More than an association

Recurrent pregnancy loss (RPL) affects close to 1% of couples; however, the etiology is known in only about 50% of the cases. Recent studies show that autoimmune dysregulation is a probable cause of RPL, which in some cases may be overlooked. In order for a pregnancy to proceed to term, early modulation of immunologic response is required to induce tolerance to the semi-allogenic fetus. Certain subsets of both the innate and adaptive immune responses play a role in the induction of fetomaternal tolerance. A relatively predominant T-cell helper (Th) 2 and T regulatory (Treg) cell population seem to favor a better pregnancy outcome, whereas Th1 and Th17 cell populations appear to have an opposite effect. Lately, the role of vitamin D in the modulation of immune response was established. Vitamin D has been shown to promote a more favorable environment for pregnancy through various mechanisms, such as enhancement of the shift toward Th2 cells and regulation of immune cell differentiation and cytokine secretion. Therefore, it seems that vitamin D deficiency sways the balance toward a worse outcome and may play a part in recurrent pregnancy loss. This review sheds light on the immunologic changes, which occur in early pregnancy and the regulatory role vitamin D has in the maintenance of this delicate balance.

Effects of micronutrients on placental function: evidence from clinical studies to animal models

Micronutrient deficiencies are common in pregnant women due to low dietary intake and increased requirements for fetal development. Low maternal micronutrient status is associated with a range of pregnancy pathologies involving placental dysfunction, including fetal growth restriction (FGR), small-for-gestational age (SGA), pre-eclampsia and preterm birth. However, clinical trials commonly fail to convincingly demonstrate beneficial effects of supplementation of individual micronutrients, attributed to heterogeneity and insufficient power, potential interactions and lack of mechanistic knowledge of effects on the placenta. We aimed to provide current evidence of relationships between selected micronutrients (vitamin D, vitamin A, iron, folate, vitamin B12) and adverse pregnancy outcomes, combined with understanding of actions on the placenta. Following a systematic literature search, we reviewed data from clinical, in vitro and in vivo studies of micronutrient deficiency and supplementation. Key findings are potential effects of micronutrient deficiencies on placental development and function, leading to impaired fetal growth. Studies in human trophoblast cells and rodent models provide insights into underpinning mechanisms. Interestingly, there is emerging evidence that deficiencies in all micronutrients examined induce a pro-inflammatory state in the placenta, drawing parallels with the inflammation detected in FGR, pre-eclampsia, stillbirth and preterm birth. Beneficial effects of supplementation are apparent in vitro and in animal models and for combined micronutrients in clinical studies. However, greater understanding of the roles of these micronutrients, and insight into their involvement in placental dysfunction, combined with more robust clinical studies, is needed to fully ascertain the potential benefits of supplementation in pregnancy.

Vitamin D, the placenta and early pregnancy: effects on trophoblast function

Pregnancy is associated with significant changes in vitamin D metabolism, notably increased maternal serum levels of active vitamin D, 1,25-dihydroxyvitamin (1,25(OH)₂D). This appears to be due primarily to increased renal activity of the enzyme 25-hydroxyvitamin D-1α-hydroxylase (CYP27B1) that catalyzes synthesis of 1,25(OH)₂D, but CYP27B1 expression is also prominent in both the maternal decidua and fetal trophoblast components of the placenta. The precise function of placental synthesis of 1,25(OH)₂D remains unclear, but is likely to involve localized tissue-specific responses with both decidua and trophoblast also expressing the vitamin D receptor (VDR) for 1,25(OH)₂D. We have previously described immunomodulatory responses to 1,25(OH)₂D by diverse populations of VDR-expressing cells within the decidua. The aim of the current review is to detail the role of vitamin D in pregnancy from a trophoblast perspective, with particular emphasis on the potential role of 1,25(OH)₂D as a regulator of trophoblast invasion in early pregnancy. Vitamin D deficiency is common in pregnant women, and a wide range of studies have linked low vitamin D status to adverse events in pregnancy. To date, most of these studies have focused on adverse events later in pregnancy, but the current review will explore the potential impact of vitamin D on early pregnancy, and how this may influence implantation and miscarriage.

Immunological function of vitamin D during human pregnancy

The well-established classic role of vitamin D is implicated in the regulation of the balance between calcium and phosphorus. Furthermore, vitamin D is also involved in many non-classic physiological processes, mainly including the regulation of cell proliferation, differentiation, apoptosis and immune function, participation in the inflammatory response and maintenance of genome stability function. During pregnancy, vitamin D receptor and its metabolic enzymes are expressed at the placenta and decidua, indicating the potential role in the mechanism of immunomodulation at the maternal-fetal interface. The insufficiency or deficiency of vitamin D may affect the mother directly and is related to specific pregnancy outcomes, such as preeclampsia, gestational diabetes, and recurrent miscarriage. This article reviews the effects of vitamin D on immune regulation during pregnancy.