Departments of Obstetrics and Gynecology, Lis Maternity Hospital and Tel Aviv Sourasky Medical Center, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
1 To whom correspondence should be addressed at: Sara Racine IVF Unit, Department of Obstetrics and Gynecology, Lis Maternity Hospital, Tel Aviv Sourasky Medical Center, 6 Weizman Street, Tel Aviv 64239, Israel. e-mail: azemf{at}tasmc.health.gov.il
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Abstract |
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Key words: failure/implantation/IVF-embryo transfer/thrombophilia
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Introduction |
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Materials and methods |
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The prevalence of thrombophilia was assessed in all 104 women. Determination of mutations in prothrombin genes, factor V Leiden and methylene tetrahydrofolate reductase (MTHFR), as well as deficiencies of protein C, protein S and antithrombin III (AT-III) were performed as described elsewhere (Kupfermine et al., 1999). Both total and free protein S assays were performed and repeated after 24 months in cases of abnormal findings. No false-positive results were found.
Since estrogen levels may alter protein S and AT-III, all thrombophilia testing was performed at least 2 months after hormonal therapy or delivery.
We routinely assess women for the presence of polycystic ovary syndrome (PCOS). The incidence of PCOS was 13%, in group A, comparable to the incidence in other patients in our unit.
None of the study participants had a history of thromboembolism.
Statistics
Statistical analysis was performed using the Pearson test, Fishers exact test and Students t-test. All test were two tailed. P < 0.05 was considered statistically significant. For sample size estimation, assuming the incidence of thrombophilias in the normal population is 16%, and assuming the rate in IVF failure patients is 40% (relative risk 2.5), with alpha of 0.05 and 80% power, 45 women are needed in each group. The data are given as mean values ± SD.
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Results |
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There were 13 cases of thrombophilia in the 21 (61.9%) women who comprised the subgroup of unexplained infertility (including four cases of homozygotic MTHFR). When comparing the prevalence of the thrombophilia in these 21 women with diagnosis of unexplained infertility without MTHFR (9/21, 42.8%) with group B (4/44), the difference was statistically significant (P = 0.002, Fishers exact test).
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Discussion |
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Several studies have shown an association between inherited thrombophilias and recurrent early pregnancy loss (Blumenfeld and Brenner, 1999; Reznikoff-Etievan et al., 2001
; Alonso et al., 2002
; Sarig et al., 2002
). There is, how ever, no consensus on the type of inherited thrombophilia associated with recurrent pregnancy loss. It was hypothesized Rey et al. (2003)
that the mechanism involved in recurrent pregnancy loss may be hypercoagulation at the implantation site, where successful connection between placenta and maternal blood should be established, thus resulting in miscarriage.
The current findings are in agreement with those of Grandone et al. (2001), who reported an association between IVF-embryo transfer failure and an increased incidence of thrombophilia. The same authors also reported that mutations of the factor V Leiden and prothrombin genes might play a role in implantation failure or in fetal loss after IVF (Grandone et al., 2001
). Bare et al. (2000)
described a higher risk of miscarriages or infertility problems in carriers of factor V Leiden. The risk of one miscarriage was 1.5-fold greater, and the risk of two or more miscarriages or infertility problems was 2.5-fold greater, for Leiden mutation carriers than for normal controls.
Finally, protein S deficiency and hypofibrinolysis were also implicated in recurrent loss and implantation failure (Glueck et al., 2000).
The precise mechanism by which thrombophilias affect recurrent pregnancy loss and implantation failure is as yet undetermined. Several studies have reported an association between hereditary thrombophilias and increased complications of pregnancy, such as severe preeclampsia, fetal growth restriction, stillbirth and abruptio placenta (Kupferminc et al., 1999; Grandone et al., 2001
). It has been suggested that thrombosis of maternal vessels and reduced perfusion to the intervillous space may contribute to these complications in association with thrombophilias (Kupferminc et al., 1999
). Invasion of maternal vessels by the syncythiotrobopblast may be affected by local microthrombosis at the site of implantation leading to implantation failure or pregnancy loss/miscarriage. It should be mentioned, however, that development of the intervillous space occurs only at 1112 weeks of gestation, making it somewhat difficult to explain implantation failure solely by thrombosis. Furthermore, Gopel et al. (2001)
showed higher ICSI success in motherchild pairs with a factor V Leiden, suggesting that a thrombotic tendency of carriers of the Leiden mutation has some advantage in fetal implantation. These latter data, however, are contrary to the recent meta analysis by Rey et al. (2003)
, which showed an association between recurrent first trimester loss and factor V Leiden.
It is unlikely that the difference in age (36.7 ± 5.9 versus 26 ± 2.3 years) between groups A and C attributed to the higher protein S deficiency rate in group A. Although protein S levels increase with age (Dykes et al., 2001), protein S deficiency was increased in the elderly patients (group A).
We analysed the data with and without MTHFR mutation, and the difference between women with IVF failure and controls was statistically significant in both cases. Although recent meta-analysis suggests that MTHFR may not be important in recurrent miscarriage (Rey et al., 2003), Nelen et al. (2000)
performed a meta-analysis to evaluate the relationship between recurrent early pregnancy loss and hyperhomocysteinaemia and the MTHFR C677T mutation. Overall, the pooled ORs for elevated homocysteine were 2.7 (95% CI 1.55.2), for afterload homocysteine 4.2 (95% CI 2.08.8) and for MTHFR 1.4 (95% CI 1.02.0). These data support hyperhomocysteinaemia as a risk factor for recurrent early pregnancy loss. Homozygosity for the MTHFR mutation represents a small increase in womens risk for recurrent pregnancy loss. Until more data emerge, the role of MTHFR is debatable. As far as AT-III, although Rey et al. (2003)
did not find an association between AT-III and fetal loss, this, as mentioned, may be due to a lack of data.
The main implication of our results, if confirmed, is that antithrombotic therapy should be evaluated in patients with IVF failure and thrombophilia.
Since thrombophilias are inherited, it is possible that fetal thrombophilia may also affect IVF-embryo transfer results. It is known that fetal thrombophilia may affect placental infarcts at a later stage of pregnancy (Dizon-Townson et al., 1997). However, with the current knowledge it is not known whether fetal thombophilia may also affect implantation.
Our findings suggest that inherited thrombophilias may play a role in the aetiology of repeated IVF-embryo transfer failure, particularly in a subgroup of women with infertility of unknown aetiology.
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Acknowledgements |
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References |
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Submitted on May, 13, 2003 ; accepted on October 7, 2003