{"paper_id":"a7274be8-dbec-4444-b1fb-d8dfe4001121","body_text":"The use of fresh or frozen embryo transfer for  in vitro \nfertilization (IVF) has been a hot topic for debate in recent decades. However,\nthere has been no definitive answer to date, given that the use of fresh or frozen\ncycles may depend on the cause of the infertility. 1 , 2  Frozen–thawed embryo transfer\n(FET) is no longer considered as merely a supplement to fresh embryo transfer, and a\n“freeze-all” protocol has become routine procedure in IVF treatment, owing to the\napplication of progestin-primed ovarian stimulation protocols and pre-implantation\ngenetic diagnosis/screening, and the higher risk of ovarian hyperstimulation\nsyndrome, higher levels of progesterone or estrogen, and abnormal endometrial status\nin fresh cycles. 3 , 4 \nThe current priority is thus to identify factors that could improve pregnancy\noutcomes in patients undergoing FET cycles.\nEndometrial preparation protocols for FET cycles can be natural or artificial.\nNatural cycles are suitable for younger women with regular ovulation, and involve\nseveral courses of hormone testing and ultrasound monitoring without medical\nintervention; however, this protocol is less easy to control and less flexible, and\ncarries a risk of asynchronization between the embryo and endometrium due to\nadvanced ovulation or anovulation. 5  Artificial or hormone replacement treatment (HRT) cycles are usually\nrecommended in older women and women with ovarian function disorders, irregular\nmenstruation cycles, or ovulation disorders. HRT cycles are more flexible than\nnatural cycles and are generally suitable for women with or without regular\novulation. Although this protocol is controlled by estrogen supplementation, it has\nbeen proved to be as successful as natural cycles. 5\nProgrammed cycles using a gonadotropin-releasing hormone agonist (GnRHa) before HRT\naim to achieve pituitary down-regulation and avoid spontaneous ovulation and cycle cancellation. 6  However, GnRHa administration increases the cost and number of treatment\ncycles, and its effect on pregnancy outcomes remains controversial. Several studies\nclaimed no difference in pregnancy outcomes between HRT and HRT with GnRHa\npretreatment, 7 – 9  and other\nprospective studies showed that pregnancy outcomes were significantly improved by\nGnRHa pretreatment in HRT cycles. 10 , 11  We therefore retrospectively\nanalyzed the outcomes of patients treated with FET cycles in our reproductive center\nand compared outcomes between HRT and HRT + GnRHa cycles.\n\nThis was a retrospective cohort analysis of women undergoing FET with HRT cycles\nat the Centre for Reproductive Medicine, Renmin Hospital of Wuhan University,\nbetween 1 January 2015 and 31 December 2017. All FET cycles in women receiving\nHRT or HRT + GnRHa cycles were included, regardless of age, diagnosis,\nstimulation protocol, embryo stage, or embryo transfer number.\nEmbryos were cryopreserved on day 3, 5, or 6 of embryo culture. The embryos were\nplaced into equilibrium solution (Kitazato Corporation, Tokyo, Japan) for 6\nminutes in room temperature, transferred to vitrification solution (Kitazato\nCorporation) for 30 s, and then loaded on a Cryotop (Kitazato Corporation) and\nplunged into liquid nitrogen within 60 s, for no longer than 90 s after initial\nexposure to vitrification solution. For thawing, the Cryotop was removed from\nliquid nitrogen and placed immediately into thawing solution (Kitazato\nCorporation) at 37°C for 1 minute, followed by a three-step rehydration\nprotocol: dilution solution for 3 minutes, followed by two steps of washing\nsolution for 5 minutes, respectively. The embryos were then transferred into a\ndroplet of blastocyst medium in a pre-balanced culture dish in 37°C and 6.0%\nCO 2 .\nArtificial preparation of the endometrium consisted of treatment with estradiol\nvalerate (Progynova®; Bayer-Schering Pharma AG, Berlin, Germany) 2 mg twice\ndaily for 7 days, followed by two mg three times daily for 6 days. Progesterone\nsupplementation was started on day 13 if the endometrium was at least 7 mm\nthick, a triple-line endometrium was present, and serum progesterone levels were\n<1.5 ng/mL. Day 3 embryos were transferred on the fourth day of progesterone\nexposure, and the blastocysts were transferred on the sixth day of progesterone\nexposure.\nFor HRT + GnRHa cycles, 3.75 mg leuprorelin acetate (Diphereline®, Ipsen, France)\nor 3.75 mg triptorelin acetate (Decapeptyl®, Ferring, Switzerland) was\nadministered during the early follicular phase of the previous menstrual cycle\n(day one or two), and the HRT protocol was started 28 days later.\nSerum β-human chorionic gonadotropin levels were measured 12 days after embryo\ntransfer. If the test was positive, daily estradiol valerate and progesterone\nsupplementation was continued until the 12th week of pregnancy. An ultrasound\nscan was performed to determine fetal viability 30 days after embryo transfer.\nClinical pregnancy was defined as the presence of at least one fetus with a\nheart beat on ultrasound 45 days after embryo transfer. Pregnancy outcomes,\nincluding information on abortion, ectopic pregnancy, delivery conditions, and\nneonatal status, were collected at clinic visits and by telephone follow-up.\nThis was a retrospective study that analyzed the electronic and paper databases\nin our hospital. All the participating partners signed informed consent for\ncontrolled ovarian hyperstimulation, oocyte and sperm collection, IVF or\nintracytoplasmic sperm injection treatment, embryo cryopreservation, embryo\ntransfer, and follow-up visits. All the procedures complied with the Regulation\nof Human Assisted Reproductive Technology in China. The data collection and\nanalysis were exempt from the need for ethical approval because the Ethical\nReview Board confirmed that it was a retrospective study with no extra\ninterventions or bias in treatment. Patient consent for data collection and\nanalysis was not required because the personal information was de-identified for\ntracking and searching.\nStatistical analysis was performed using IBM SPSS Statistics for Windows, version\n19.0 (IBM Corp., Armonk, NY, USA). Continuous variables were analyzed using\nindependent  t -tests or Mann–Whitney U tests, depending on the\nnormality of the distribution. Categorical variables were analyzed by Pearson’s\nχ 2  or Fisher’s exact tests.  P <0.05 indicated\nstatistical significance.\n\nA total of 3239 FET cycles were evaluated and included in this study, including\n2936 HRT cycles and 303 HRT + GnRHa cycles. The baseline characteristics of both\ngroups are presented in  Table 1 . The average age was significantly higher in the HRT + GnRHa\ncompared with the HRT group ( P <0.0001) and the proportion of\nolder women (>35 years) was also significantly higher in the HRT + GnRHa\ngroup ( P <0.0001). The proportion of women with endometriosis\nwas significantly higher and the endometrial thickness on the\nprogesterone-administration day was significantly lower in the HRT + GnRHa\ncompared with the HRT group (both  P  < 0.0001). The type of\ninfertility, number of FET cycles, number of transferred embryos and type of\nembryos, and serum estradiol level on the progesterone-administration day were\nall similar in both groups.\nBaseline characteristics of women receiving HRT or HRT + GnRHa.\nData presented as mean ± standard error or n\n(%). a Student’s\n t -test; b Pearson’s χ 2  test.\nHRT, hormone replacement treatment; GnRHa, gonadotropin-releasing\nhormone agonist; PCOS, polycystic ovarian syndrome; POF, premature\novarian failure; FET, frozen-thawed embryo transfer; E 2 ,\nestradiol.\nThe pregnancy outcomes are presented in  Table 2 . The overall clinical pregnancy\nrate (CPR) and live birth rate (LBR) were similar in the two groups. However,\namong younger women (≤35 years), the CPR was significantly higher in the\nHRT + GnRHa group ( P  = 0.04), but the LBR remained similar in\nboth groups. Among older women, the LBR was slightly lower in the HRT + GnRHa\ncompared with the HRT group, but the difference was not significant. The\nabortion rate and sex ratio at birth (female versus male) were similar in both\ngroups.\nPregnancy outcomes in women receiving HRT or HRT + GnRHa in relation to\nage.\nData presented as mean ± standard error.  a Pearson’s\nχ 2  test. HRT, hormone replacement treatment; GnRHa,\ngonadotropin-releasing hormone agonist.\nThe pregnancy outcomes in women with endometriosis and polycystic ovarian\nsyndrome (PCOS) are shown in  Table 3 . Among women with\nendometriosis, the CPR and LBR were both significantly higher in the HRT + GnRHa\ngroup compared with the HRT group ( P =0.04 and\n P  = 0.02, respectively). Among women with PCOS, the CPR and\nLBR were comparable in the two groups, but the abortion rate was significantly\nlower in the HRT + GnRHa group ( P  = 0.04).\nPregnancy outcomes in women with endometriosis or PCOS receiving HRT or\nHRT + GnRHa.\nData presented as mean ± standard error.  a Student’s\n t -test;  b Pearson’s χ 2 \ntest. HRT, hormone replacement treatment; GnRHa,\ngonadotropin-releasing hormone agonist; PCOS, polycystic ovarian\nsyndrome.\n\nIn this study, we analyzed 3239 FET cycles to compare the pregnancy outcomes between\nwomen receiving HRT cycles and HRT + GnRHa cycles. CPR and LBR were similar in both\nHRT protocols, with or without GnRHa pretreatment. However, given that this was a\nretrospective study with significant differences in participants’ ages and\ninfertility diagnoses, the results must be interpreted with caution.\nGnRHa may be given in addition to HRT to suppress hormone production by the ovaries\nand inhibit spontaneous ovulation in artificial cycles. In this study, the average\nage was significantly higher in the HRT + GnRHa group compared with the HRT group.\nAccording to feedback from clinic physicians, this was partly because GnRHa\npretreatment could prolong the menstruation cycle and decrease the cycle\ncancellation rate in older women. A previous retrospective study also found that the\naverage age of women undergoing FET cycles with GnRHa pretreatment was higher than\nthat for women undergoing cycles without GnRHa, because physicians preferred to use\nGnRHa to prevent cancellation in women of advanced age. 8\nNatural and artificial FET cycles can achieve equivalent pregnancy outcomes in women\nwith regular ovulation and well-preserved ovarian function. 12 , 13  A prospective\nrandomized clinical trial found no difference in pregnancy outcomes between HRT\ncycles with and without GnRHa pretreatment in women with regular menstrual cycles. 7  HRT cycles can therefore be applied in younger women with normal ovulation\nand ovarian reserve function, to minimize clinic visiting times and costs. However,\nthe LBR was slightly lower and the abortion rate was higher among older women\n(>35 years) receiving HRT + GnRHa compared with HRT. Likewise, in controlled\nhyperstimulation ovulation, a long pituitary-suppression protocol with GnRHa did not\nproduce favorable results in older women or women with poor ovarian reserve,\npossibly because GnRHa may cause over-suppression of hypothalamic-pituitary-ovarian\nfunction and negatively affect uterine receptivity. 14 – 16  The effect of GnRHa\npretreatment on pregnancy outcomes in women older than 35 years needs to be further\nvalidated.\nEndometriosis is a main reason for sub-fertility and failure of embryo\nimplantation. 13 , 17  GnRHa has been used to treat endometriosis by long-term\npituitary suppression to improve uterine receptivity. 18 – 20  In this study, HRT cycles with\nGnRHa pretreatment significantly increased the CPR and LBR in women with\nendometriosis. Previous results also suggested that FET following GnRHa treatment\ntended to increase the pregnancy rate in women with endometriosis or\nadenomyosis. 21 , 22\nInfertile women with PCOS have an increased risk of early pregnancy loss, possibly as\na result of hyperandrogenism, aberrant uterine receptivity, insulin resistance, and\nhigh body mass index. 23 – 25  In terms of\nIVF treatment, women with PCOS are usually transferred to FET cycles because of a\nhigh risk of ovarian hyperstimulation syndrome, and it is important to decrease the\nrate of pregnancy loss in women with PCOS. 26  In this study, although the abortion rate among women with PCOS was\nsignificantly higher in the HRT group compared with the HRT + GnRHa group, the LBR\nwas similar in both groups, possibly because of the small sample size in the\nHRT + GnRHa group. A previous retrospective study showed that GnRHa pretreatment\nduring FET significantly increased the ongoing pregnancy rate in women with\nhyperandrogenic PCOS. 27  However, testosterone levels were not monitored in women with PCOS to\ndetermine the mechanism of GnRHa in the prevention of pregnancy loss.\n\nWe recommend that women undergoing FET be treated individually in terms of\nendometrial preparation, based on their diagnosis and age. GnRHa pretreatment could\nsignificantly increase CPR and LBR in women with endometriosis and decrease the\nabortion rate in women with PCOS. However, this was a retrospective clinical study\nwith a limited sample size in the HRT + GnRHa group, and further prospective,\nrandomized clinical studies are needed to validate the optimal protocol for FET\ncycles.","source_license":"CC0","license_restricted":false}