To compare the clinical outcomes of infertile patients with and without syphilis after in vitro fertilization and embryo transfer (IVF-ET), in this case-control study, 320 infertile couples were enrolled and divided into syphilis (n = 160) and control groups (n = 160). The primary IVF outcomes were the clinical pregnancy rate and the birth of a healthy baby. All syphilis patients received the standard anti-syphilis treatment before undergoing IVF/ICSI. Our results showed that the endometrial thickness of the syphilis group was greater than that of the control group following hCG injection (16.9±5.4 vs. 13.0±4.7 mm, P<0.001). The numbers of normally fertilized eggs and normally cleaved fertilized eggs and the implantation rate were 6.8±4.8, 6.3±4.7 and 24.2%, respectively, for the syphilis group and 8.3±4.6, 8.1±4.6 and 34.4%, respectively, for the control group, and these values were significantly different between the groups. The clinical pregnancy rate was lower in the syphilis group compared with that in the control group (43.8% vs. 55.6%, P = 0.03). Lower offspring birth weight was observed in the infected male group compared with those in the infected female (2.7±0.4 vs. 3.0±0.4 kg, P = 0.01) and infected couple groups (2.7±0.4 vs. 3.1±0.5 kg, P = 0.007). Therefore, syphilis infection reduces the clinical pregnancy rate after IVF/ICSI.
Citation: Wang J, Zhao X, Yuan P, Fang T, Ouyang N, Li R, et al. (2015) Clinical Outcomes of In Vitro Fertilization among Chinese Infertile Couples Treated for Syphilis Infection. PLoS ONE 10(7): e0133726. https://doi.org/10.1371/journal.pone.0133726
Editor: Norbert Gleicher, Center for Human Reproduction, UNITED STATES
Received: January 7, 2015; Accepted: June 16, 2015; Published: July 24, 2015
Copyright: © 2015 Wang et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Data Availability: Data are available upon request due to ethical restrictions protecting patients' privacy. The ethics committee of the Sun Yat-sen Memorial Hospital can be reached at the following telephone number: 86-020-81332371. Readers can also contact the corresponding author (Wenjun Wang, e-mail:firstname.lastname@example.org) to request data from the ethics committee.
Funding: This study was funded by The National Science Technology Research Projects of China(81100402) and The Specialized Research Funds for New Teachers Program of the Chinese Ministry of Education(20110171120083). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
Syphilis is a sexually transmitted disease (STD) caused by Treponema pallidum, and it is primarily spread through sexual intercourse[1,2], blood transfusion or maternal-neonatal transmission. The incidence rate of syphilis has risen rapidly in China since 1978[5,6], and it has become the most common STD in economically developed regions. Syphilis infection of the reproductive tractcan cause inflammatory disease and infertility. Reproductive tract infection and inflammation cause 8% and 35% of all cases of male infertility, respectively. In women, it can result in fallopian tube obstruction[11,12] and endometritis. Approximately 72.4 million people worldwide have infertility problems. In vitro fertilization (IVF) may be the last resort for couples attempting to overcome infertility[14,15]. The relationship between syphilis and infertility has been rarely reported in the literature. One previous report on the effects of syphilis on IVF outcome has shown lower fertilization and implantation rates due to infection of the male parent with latent syphilis compared with the rates in those without syphilis infection. However, women with syphilis were not included in the study. Therefore, we performed retrospective analysis of patients who received IVF/intra-cytoplasmic sperm injection (ICSI) to evaluate the effects of syphilis on IVF-embryo transfer (ET) outcome.
Materials and Methods
All patients in this study provided written informed consent for the use of their medical records. The Ethics Committee of the Sun Yat-Sen Memorial Hospital approved this study.The ethics committee approval of the Sun Yat-sen Memorial Hospital  Record of ethics committee No. (02) Reproductive medicine centre: After censored by the medical ethics committee of the Sun Yat-sen Memorial Hospital, the clinical research project of your department “The effect of syphilis infection to outcomes of IVF: a retrospective case-control study” was approved to be carried out based on the retrospective study according with the requirements of medical ethics. Medical Ethics Committee 16 January 2014. In this retrospective case-control study, clinical data were obtained from 320 infertile couples presenting to Sun Yat-Sen Memorial Hospital between January 2008 and March 2014. The patients were divided into a syphilis group(n = 160) and a control group(n = 160)(age-matched at a ratio of 1:1). The syphilis group was divided into the following three subgroups: the infected male group (couples in which the male was anti-syphilis antibody-positive and the female was healthy, n = 69), the infected female group (couples in which the female was anti-syphilis antibody-positive and the male was healthy, n = 65), and the infected couple group (both partners were infected, n = 26). No interventional treatments were performed.
Couples who failed to conceive after at least 1 year of intercourse without contraception were considered to be infertile. Infertility was caused by fallopian tube dysfunction and/or male-related factors (a diagnosis of asthenozoospermia and/or asthenoteratozoospermia or azoospermia according to the WHO Laboratory Manual for the Examination and Processing of Human Semen[17,18]). All patients underwent fresh ET during the first cycle and did not receive any medication for 3 months prior to IVF/ICSI. Patients were excluded if they had hysteromyoma, adenomyosis, ovarian tumor, endometriosis, polycystic ovarian syndrome (PCOS), hyperprolactinemia, thyroid disease, adrenal disease, diabetes, or a chromosomal aberration(determined by karyotype). Women with a reproductive tract abnormality or uterine malformation and those with a sperm or egg donor were also excluded.
Ovarian function was examined, and peripheral blood samples were collected on days 2–4 of menstruation to examine the basic follicle-stimulating hormone (bFSH), basic luteinizing hormone (bLH), and estrogen (E2) levels. Ultrasonography was performed to determine the antral follicle count (AFC). Routine semen and sperm morphology tests were conducted. All participants received laboratory serologic examinations (the rapid plasma reagin [RPR] and/or Treponema pallidum particle agglutination [TPPA] tests) to test for the presence of syphilis infection prior to the IVF/ICSI treatment.
All serum samples were first assessed using a non-Treponema pallidum antigen serologic (RPR) test to screen for syphilis, and then a Treponema pallidum antigen serologic (TPPA) test was conducted to confirm the syphilis-positive samples identified by the screening test[19,20,21]. For the RPR test, cardiolipin is used as an antigen to detect anti-cardiolipin antibodies in the serum. All serum samples for the RPR test were progressively diluted (1:1 to 1:32) in normal saline for titer determination. In the TPPA test, gelatin granules sensitized to Treponema pallidum bind to anti-Treponema pallidum antibodies in human serum. The combination of the RPR and TPPA tests is widely used for the maximal detection of syphilis during all phases of the disease with adequate sensitivity and specificity.
The patients were divided into the syphilis and control groups based on the laboratory serologic results. The patients in the syphilis group with a history of syphilis treatment (according to medical records) but no history of re-exposure did not receive syphilis treatment in this study. An anti-syphilis treatment (penicillin G20) was administered to the patients without a history of syphilis infection and with positive RPR or TPPA results. A 4-fold (2 dilutions) or greater decrease in the anti-Treponema pallidum antibody titer was indicative of treatment efficacy. This titer remained stable over a long period of time in the few patients who received the standard anti-syphilis treatment, a phenomenon known as “fixed serology”, if the patients without clinical signs of relapse were not treated with anti-syphilis therapy. The patients received IVF/ICSI treatment at one month after the disappearance of their clinical syphilis symptoms or after their Treponema pallidum antigen serologic test results became negative. Some patients remained positive for Treponema pallidum-specific antibody after the anti-syphilis treatment. Couples were included in the control group if both patients showed negative RPR and TPPA results.
Controlled ovarian hyperstimulation
The mid-luteal long protocol was employed as follows : a 1.87 mg dose of long-acting GnRH-a (Diphereline; Ipsen Pharma Biotech, Signes, France) was administered during the prior mid-luteal menstrual cycle to promote pituitary downregulation, as determined byblood E2 <50 ng/L, LH <5 IU/L, FSH <5 IU/L, and ultrasound-detected vaginal endometrial thickness <5 mm. Gonadotropin (Gn) was administered at 14 days after downregulation to promote follicle development. The Gn dosage was determined based on patient age, the basal FSH level, BMI, and the AFC, and 150–300 IU/d recombinant human FSH (Gonal-F; Merck Serono, Geneva, Switzerland) was administered. During ovarian hyperstimulation, the blood E2, progesterone, and LH levels were measured, and follicle development was monitored by transvaginal ultrasound (ALOKA 3500, Japan). When three follicles with ≥16 mm diameters, two follicles with ≥17 mm diameters, or one follicle with a ≥18 mm diameter was detected on ultrasound, 10,000 IU human chorionic gonadotropin (hCG) (Livzon, Zhuhai, China) was administered on that evening. Ultrasound-guided transvaginal oocyte retrieval was conducted at 34 to 36 hours after hCG injection, and a sperm sample was concurrently collected and subjected to density gradient centrifugation. The fertilization regimen and traditional IVF and ICSI fertilization protocols used were selected based on the concentration and motility of the washed sperm. No special ovulation or sperm washing procedures were performed for the antibody-positive patients without a recent syphilis reinfection.
Embryo grading and transfer
Embryo morphology evaluations were conducted by monitoring the pronuclei for 17±1 hours after fertilization. Embryo cleavage and development were monitored for 44±1 hours and 68±1 hours after fertilization, respectively. Optimal embryos that met the quality screening criteria did not exhibit multiple pronuclei; rather, they showed 4–5 blastomeres of homogenous sizes with an accumulation of <5% cell debris by day 2 and 7–9 blastomeres of homogenous sizes with an accumulation of <5% cell debris by day 3. Ultrasound-guidedET was conducted on day 3 after oocyte retrieval. When available, two embryos were transferred into the women who were <35 years old, and three embryos were transferred into those who were ≥35 years old.
Luteal support was achieved via daily intramuscular injections of progesterone (60 mg/day) (Progesterone Injection, Xian Ju Pharmaceutical Co., Zhejiang, China) following oocyte retrieval for up to 14 days after ET. Serum β-hCG was tested on day 14 after ET, and progesterone administration was continued for 12 weeks after diagnosis of pregnancy. Ultrasonography was conducted at 35 days after ET, and clinical pregnancy was diagnosed via the presence of an intrauterine gestational sac, fetal bud, and fetal heartbeat; otherwise, biochemical diagnosis was performed.
We reviewed the patients’ medical records to obtain information about their hospital and telephone follow-up assessments.
The collected data were analyzed using SPSS 21.0. A total of 3,275 couples with no history of syphilis infection were included. We selected 160 patients from the 3,275 couples to form the control group. First, the 3,275 couples were divided into 20 groups based on age (range of 24–43 years), according to the age range of the syphilis group, and then random patient numbers were generated for each age group using SPSS 21.0 with the seed set to (1,100) and inclusion of four decimal places in the random numbers. According to the number of patients in each syphilis age group, 160 patients were extracted  from the randomly generated numbers in ascending order by stratified random sampling to form the control group. The t-test was used to perform between-group comparisons of the normally distributed quantitative datasets with homogeneous variances, and the results are presented as the mean ± standard deviation. The Mann-Whitney test was conducted to analyze the non-normally distributed datasets, and the results are presented as medians with ranges. Analysis of variance was applied to compare the means of the three quantitative subgroups when that data for each sample was normally distributed with a homogeneous variance. The least significant difference (LSD) test was used to perform pairwise comparisons between any two of the three groups, and the results are presented as the mean ± standard deviation. The Kruskal-Wallis test was conducted to assess non-normally distributed data among the three subgroups or those that did not exhibit homogeneous variances, and the results are presented as medians with ranges. The chi-square test was carried out to assess the qualitative data, and the results are reported as percentiles. Binary analyses were conducted using logistic regression, and factors were introduced into the regression equation using the Enter method. All results were considered significant (two-tailed) at P<0.05.
Clinical characteristics of the syphilis and control groups
No significant differences were found in female age (P = 0.99), duration of infertility (P = 0.50), BMI (P = 0.15), or the basal FSH (P = 0.12), basal LH (P = 0.59) or basal E2 level (P = 0.81) between the syphilis and control groups. Endometrial thickness on the hCG injection day was significantly higher for the syphilis group compared with the control group (16.9±5.4 vs. 13.0±4.7 mm, P<0.001). Syphilis infection likely affected endometrial thickness (Table 1).
Laboratory parameters and clinical outcomes of the syphilis and control groups
The number of normal fertilizations (6.8±4.8 vs. 8.3±4.6, P = 0.004), number of oocytes with normal cleavage (6.3±4.7 vs. 8.1±4.6, P = 0.001) and implantation rate (24.2% vs. 34.4%, P = 0.003) significantly differed between the syphilis and control groups. The clinical pregnancy rate was significantly lower in the syphilis group compared with the control group (43.8% vs. 55.6%, P = 0.03), and the biochemical pregnancy rate was higher in the syphilis group (7.5% vs. 0.6%, P = 0.002) (Table 2).
Clinical characteristics, laboratory parameters, and clinical outcomes of the three subgroups
No significant differences in age (P = 0.25), the duration of infertility (P = 0.23), basal FSH level (P = 0.52), basal E2 level (P = 0.31), total dosage of Gn (P = 0.79), number of retrieved oocytes (P = 0.38), or early miscarriage rate (P = 0.81) were found among the infected women, infected men, and infected couple subgroups. Fetal birth weight (P = 0.006) significantly differed among the three subgroups. Furthermore, the LSD test revealed that the fetal birth weight was significantly lower for the offspring of the infected males compared with those of the infected females (2.7±0.4 vs. 3.0±0.4 kg, P = 0.01) and couples (2.7±0.4 vs. 3.1±0.5 kg, P = 0.007). The average gestational period was also shorter in the infected male group compared with the infected female (36.5±1.4 vs. 37.9±1.5 kg, P<0.001) and couple groups (36.5±1.4 vs. 38.1±1.6 kg, P = 0.003). Fetal birth weight at delivery <37 weeks was significantly higher in the couple group compared the infected female (3.3±0.3 vs. 2.7±0.4 kg, P = 0.01) and infected male groups (3.3±0.3 vs. 2.4±0.2 kg, P = 0.001). No differences in the clinical pregnancy rate were detected among the subgroups (women: 43.1% vs. men: 44.9% vs. couples: 42.3%, P = 0.96) (Table 3).
Logistic regression analysis of the clinical pregnancy rate
Logistic regression analysis was performed to evaluate the confounding factors for the clinical pregnancy rate. We found that the presence of syphilis (OR: 0.615, 95% CI: 0.382–0.991, P = 0.046), female age (OR: 0.895, 95% CI: 0.838–0.955, P = 0.001), and BMI (OR: 1.124, 95% CI: 1.023–1.235, P = 0.015) all influenced this rate (Table 4).
Age is related to ovarian response as well as the quality and quantity of embryos. Increased age appears to be a key predictor of worse assisted reproductive therapy (ART) outcome. In our study, we matched the ages of the subjects in the control and syphilis groups to avoid the confounding influence of age on the results. Our results showed that on the day of hCG injection, the mean endometrial thickness of the syphilis group was significantly higher than that of the control group. Moreover, the clinical pregnancy rate of the syphilis group was significantly lower than that of the control group. These results imply that the endometrial thickness of the syphilis group on hCG injection day was not conducive to pregnancy. Studies have shown that a triple-line pattern combined with an optimal endometrial thickness (7–14 mm) is associated with a positive pregnancy outcome. Okohue JE et al. have reported that the pregnancy rate is significantly higher in women with an endometrial thickness of 7–14 mm compared with those with a thickness of >14 mm. They suggested that endometrial thickness affects the clinical pregnancy rate, potentially due to infection and inflammation caused by endometrial damage. Syphilis (as an STD) can cause pelvic inflammatory diseases, which can lead to endometrial damage. Furthermore, this damage results in repeated repair and regeneration processes, which may thicken the endometrial lining and lead to abnormal endometrial functioning and reduced endometrial receptivity, resulting in infertility[33,34]. In addition, the numbers of normally fertilized oocytes and normally cleaved oocytes as well as the implantation rate were significantly lower for the syphilis group compared with the control group, and these findings may be related to pelvic inflammation, which may reduce the implantation rate. Improvements in endometrial receptivity may increase the clinical pregnancy rate achieved by ART. Therefore, physicians should assess the endometrium of infertile syphilis patients. Appropriate examinations and treatments for endometrial thickness or morphological abnormalities should be performed to improve clinical outcome.
The objective of IVF is to produce a healthy live born baby. In our study, one deformity was detected in the offspring of the subjects in the syphilis group, while none were observed in those of the subjects in the control group; however, due to the limited sample size, there were no significant differences between the two groups, further study is necessary to better characterize the deformity rate. Syphilis can cause miscarriage, but our results did not show significant differences in early miscarriage and the average fetal gestational period between the syphilis and control groups. These results may have been due to the systemic and standard anti-syphilis treatments that the syphilis patients had received prior to IVF treatment. Importantly, the number of mature oocytes and the rates of clinical pregnancy, biochemical pregnancy, and early miscarriage did not significantly differ among the subgroups, indicating that the IVF-related clinical outcomes of the couples with a positive history of syphilis were not influenced by whether the woman, man, or both were infected. Positive serology in the male group was associated with a lower offspring birth weight and shorter average gestational period compared with that in the female and couple groups; however, the reason for this finding is currently unclear.
Because most patients do not show clinical symptoms and are not aware of their syphilis infection, the CDC recommends that individuals with multiple sexual partners should undergo a syphilis screening at least once per year. All women should be tested for Treponema pallidum during their first prenatal examination and again late in pregnancy. ART patients should receive routine syphilis serology testing. If the results are positive, the couples should receive standard anti-syphilis treatment, and be informed of the unfavorable IVF pregnancy outcome due to the infection. If the embryos require cryopreservation, a closed loading device should be used to avoid iatrogenic cross-infection in the hospital.
In addition, anti-cytokine antibodies (ACAs) and cytokines may also affect the fecundity of syphilis patients to a certain extent. ACAs are often found in the serum of these patients and can inhibit the differentiation of cytotrophoblasts into syncytiotrophoblasts, thereby damaging cultivated blastocysts. Cytokines are closely related to every aspect of the reproductive process and can be used to predict the clinical outcome of IVF. Studies have shown that immunological changes occur in humans following Treponema pallidum infection; specifically, T helper cells are biased toward the Th1 phenotype in the peripheral blood of syphilis-infected individuals, and TNF-α secretion is significantly increased but is significantly reduced after treatment. In a future study, changes in the ACA and cytokine levels should be assessed, which may represent an additional means of investigating the mechanisms underlying the influence of syphilis infection on ART success.
Limitations: Our syphilis group was composed of 160 patients, the sample sizes of each of the three syphilis subgroups were small, which may explain the lack of significant differences observed among them for most of the parameters tested.
A positive history of syphilis infection can reduce the clinical pregnancy rate following IVF/ICSI. We have shown that this reduction in the clinical pregnancy rate involves a variety of factors, including endometrial thickness, the number of mature oocytes, the number of fertilized, normally cleaved oocytes, and the implantation rate. However, the mechanisms underlying the effects of syphilis on IVF success are currently unclear. Future studies should use larger sample sizes to better elucidate these mechanisms.
Syphilis infection reduces the clinical pregnancy rate after IVF/ICSI. The endometrial thickness and implantation rate of infertile couples treated for syphilis infection may be the most important factors affecting IVF outcome.
S2 File. Translation of hospital ethics committee approval.
The authors thank Huang Baoyun for assisting with data collection, as well as Pi Guo for performing statistical analyses.
Conceived and designed the experiments: JW WW. Performed the experiments: JW WW. Analyzed the data: JW WW XZ PY. Contributed reagents/materials/analysis tools: TF NO RL SO. Wrote the paper: JW WW. Revised and approved the final version for publication: WW. Collected data: JW XZ PY TF NO RL SO WW.
- 1. Lafond RE, Lukehart SA. Biological basis for syphilis. Clin Microbiol Rev. 2006; 19(1):29–49. pmid:16418521
- 2. Munkhzul B, Batdorj B, Baigalmaa J. An outbreak of syphilis in Darkhan-Uul, Mongolia, January to March. Western Pac Surveill Response J. 2012; 3(4):48–52. pmid:23908940
- 3. Wang BX, Zhang L, Wang YJ, Yan JW, Wan YN, Peng WJ, et al. Epidemiology of syphilis infection among drug users at methadone maintenance treatment clinics in China: systematic review and meta-analysis. Int J STD AIDS. 2013; 25(8):550–558. pmid:24352128
- 4. Lee SH, Kim JH, Kim SC. Early congenital syphilis presenting with vesicobullous eruptions beyond palmoplantar regions. Acta Derm Venereol. 2014; 94(3):321–322. pmid:24037177
- 5. Chen XS, Yin YP, Wang QQ, Wang BX. Historical perspective of syphilis in the past 60 years in China: eliminated, forgotten, on the return. Chin Med J (Engl). 2013; 126(14):2774–2779.
- 6. Zhang L, Liang S, Lu W, Pan SW, Song B, Liu Q, et al. HIV, syphilis, and behavioral risk factors among female sex workers before and after implementation of harm reduction programs in a high drug-using area of China. PLOS ONE. 2014; 9(1):e84950. pmid:24416319
- 7. Yang LG, Tucker JD, Yang B, Shen SY, Sun XF, Chen YF, et al. Primary syphilis cases in Guangdong Province 1995–2008: opportunities for linking syphilis control and regional development. BMC Public Health. 2010; 10(793).
- 8. Wilkinson D, Ndovela N, Harrison A, Lurie M, Connolly C, Sturm AW. Family planning services in developing countries: an opportunity to treat asymptomatic and unrecognised genital tract infections. Genitourin Med. 1997; 73(6):558–560. pmid:9582484
- 9. Almobarak AO, Elhoweris MH, Nour HM, Ahmed MA, Omer AF, Ahmed MH. Frequency and patterns of abnormal Pap smears in Sudanese women with infertility: What are the perspectives. J Cytol. 2013; 30(2):100–103. pmid:23833398
- 10. Askienazy-Elbhar M. Male genital tract infection: the point of view of the bacteriologist. Gynecol Obstet Fertil. 2005; 33(9):691–697. pmid:16137914
- 11. Kiguli-Malwadde E, Byanyima RK. Structural findings at hysterosalpingography in patients with infertility at two private clinics in Kampala, Uganda. Afr Health Sci. 2004; 4(3):178–181. pmid:15687070
- 12. Zhao WH, Hao M. Pelvic inflammatory disease: a retrospective clinical analysis of 1,922 cases in North China. Gynecol Obstet Invest. 2014; 77(3):169–175. pmid:24556824
- 13. Boivin J, Bunting L, Collins JA, Nygren KG. International estimates of infertility prevalence and treatment-seeking: potential need and demand for infertility medical care. Hum Reprod. 2007; 22(6):1506–1512. pmid:17376819
- 14. Jin X, Wang G, Liu S, Zhang J, Zen F, Qiu Y, et al. Survey of the situation of infertile women seeking in vitro fertilization treatment in China. Biomed Res Int. 2013; 179098. pmid:24369006
- 15. Lam PM, Suen SH, Lao TT, Cheung LP, Leung TY, Haines C. Hepatitis B infection and outcomes of in vitro fertilization and embryo transfer treatment. Fertil Steril. 2010; 93(2):480–485. pmid:19324342
- 16. Li L, Li SW, Huang ZY, Wang Y, Xiao Z, Fan W, Outcomes of in vitro fertilization-embryo transfer in men with latent syphilis. Shangdong Medical Journal 2013;17:18–19
- 17. WHO. WHO laboratory manual for the Examination of Human Semen and Semen-Cervical Mucus Interaction. 4th edn. Cambridge:Cambridge University Press.1999; 204.
- 18. WHO. WHO laboratory manual for the Examination and processing of human semen. 5th edn.Geneva;World Health Organization,2010; 224.
- 19. Lee V, Kinghorn G. Syphilis: an update. Clin Med. 2008; 8(3):330–333. pmid:18624050
- 20. Workowski KA, Berman S. Sexually transmitted diseases treatment guidelines, 2010. MMWR Recomm Rep. 2010; 59(RR-12):1–110. pmid:21160459
- 21. Jiang C, Zhao F, Xiao J, Zeng T, Yu J, Ma X, et al. Evaluation of the recombinant protein TpF1 of Treponema pallidum for serodiagnosis of syphilis. Clin Vaccine Immunol. 2013; 20(10):1563–1568. pmid:23945159
- 22. Sena AC, White BL, Sparling PF. Novel Treponema pallidum serologic tests: a paradigm shift in syphilis screening for the 21st century. Clin Infect Dis. 2010; 51(6):700–708. pmid:20687840
- 23. Tong ML, Lin LR, Liu GL, Zhang HL, Zeng YL, Zheng WH, et al. Factors associated with serological cure and the serofast state of HIV-negative patients with primary, secondary, latent, and tertiary syphilis. PLOS ONE. 2013; 8(7):e70102. pmid:23894598
- 24. Smit PW, Mabey D, Changalucha J, Mngara J, Clark B, Andreasen A,et al. The trade-off between accuracy and accessibility of syphilis screening assays. PLOS ONE. 2013; 8(9):e75327. pmid:24066175
- 25. Chen H, Wang W, Mo Y,Ma Y, Ouyang N, Li R, et al. Women with high telomerase activity in luteinised granulosa cells have a higher pregnancy rate during in vitro fertilisation treatment. J Assist Reprod Genet. 2011; 28(9):797–807. pmid:21717175
- 26. The Istanbul consensus workshop on embryo assessment: proceedings of an expert meeting. Hum Reprod. 2011; 26(6):1270–1283. pmid:21502182
- 27. Fang J. Statistical Methods for Biomedical Research. 1st edn,2007. Higher Education Press. Beijing, China. 2007; 266.
- 28. Bhattacharya S, Maheshwari A, Mollison J. Factors associated with failed treatment: an analysis of 121,744 women embarking on their first IVF cycles. PLOS ONE. 2013; 8(12):e82249. pmid:24349236
- 29. Zhao J, Zhang Q, Li Y. The effect of endometrial thickness and pattern measured by ultrasonography on pregnancy outcomes during IVF-ET cycles. Reprod Biol Endocrinol. 2012; 10:100. pmid:23190428
- 30. Okohue JE,Onuh SO, Ebeigbe P, Shaibu I, Wada I, Ikimalo JI, et al. The effect of endometrial thickness on in vitro fertilization (IVF)-embryo transfer/intracytoplasmic sperm injection (ICSI) outcome. Afr J Reprod Health, 2009; 13(1); 113–21. pmid:20687269
- 31. Deiss RG, Leon SR, Konda KA, Brown B, Segura ER, Galea JT, et al. Characterizing the syphilis epidemic among men who have sex with men in Lima, Peru to identify new treatment and control strategies. BMC Infect Dis. 2013; 13:426. pmid:24016185
- 32. Quentin R, Verdon R. Microbiologic basis of diagnosis and treatment of pelvic inflammatory disease. J Gynecol Obstet Biol Reprod (Paris). 2012; 41(8):850–863.
- 33. Cicinelli E, De Ziegler D, Nicoletti R, Tinelli R, Saliani N, Resta L, Bellavia M, et al. Poor reliability of vaginal and endocervical cultures for evaluating microbiology of endometrial cavity in women with chronic endometritis. Gynecol Obstet Invest. 2009; 68(2):108–115. pmid:19521097
- 34. Kasius JC, Broekmans FJ, Sie-Go DM, Bourgain C, Eijkemans MJ, Fauser B C, et al. The reliability of the histological diagnosis of endometritis in asymptomatic IVF cases: a multicenter observer study. Hum Reprod. 2012; 27(1):153–158. pmid:22025228
- 35. Karimzade MA, Oskouian H, Ahmadi S, Oskouian L. Local injury to the endometrium on the day of oocyte retrieval has a negative impact on implantation in assisted reproductive cycles: a randomized controlled trial. Arch Gynecol Obstet. 2010; 281(3):499–503. pmid:19568761
- 36. Casper RF. It's time to pay attention to the endometrium. Fertil Steril. 2011; 96(3):519–521. pmid:21880272
- 37. Chen XS, Peeling RW, Yin YP, Mabey D. Improving antenatal care to prevent adverse pregnancy outcomes caused by syphilis. Future Microbiol. 2011; 6(10):1131–1134. pmid:22004031
- 38. Tucker JD, Chen XS, Peeling RW. Syphilis and social upheaval in China. N Engl J Med. 2010; 362(18):1658–1661. pmid:20445179
- 39. CDC Factsheet:Reported STDs in the United States:2012 National Data for Chlamydia,Gonorrhea,andSyphilis.Centersfor Disease Control and Prevention,2014
- 40. U.S. PSTF. Screening for syphilis infection in pregnancy: U.S. Preventive Services Task Force reaffirmation recommendation statement. Ann Intern Med. 2009; 150(10):705–709. pmid:19451577
- 41. Borkhardt HL, Zielinski S. Influence of cardiolipin antibodies on the binding of treponemal specific antibodies in the fluorescence treponemal antibody absorption test and the Treponema pallidum immobilisation test. J Med Microbiol. 1997; 46(11):965–972. pmid:9368539
- 42. Di SN, Meroni PL, de Papa N, Raschi E, Caliandro D, De Carolis CS, et al. Antiphospholipid antibodies affect trophoblast gonadotropin secretion and invasiveness by binding directly and through adhered beta2-glycoprotein I. Arthritis Rheum. 2000; 43(1):140–150. pmid:10643710
- 43. Hammadeh ME, Ertan AK, Zeppezauer M, Baltes S, Georg T, Rosenbaum P, et al. Immunoglobulins and cytokines level in follicular fluid in relation to etiology of infertility and their relevance to IVF outcome. Am J Reprod Immunol. 2002; 47(2):82–90. pmid:11900592
- 44. Arroll TW, Centurion-Lara A, Lukehart SA, Van Voorhis WC. T-Cell responses to Treponema pallidum subsp. pallidum antigens during the course of experimental syphilis infection. Infect Immun. 1999; 67(9):4757–4763. pmid:10456928
- 45. Knudsen A, Benfield T, Kofoed K. Cytokine expression during syphilis infection in HIV-1-infected individuals. Sex Transm Dis. 2009; 36(5):300–304. pmid:19265730