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The increasing use of frozen–thawed embryo transfer (FET) cycles has magnified the focus on endometrial preparation protocols in assisted reproduction. Emerging evidence suggests that natural cycle (NC) FETs are associated with improved outcomes, and that providers should consider increasing the utilization of NC FET at the expense of the currently favored artificial cycle (AC) FET as primary method for endometrial preparation.

Purpose The purpose of this study is to evaluate the freeze-all strategy in subgroups of normal responders, to assess whether this strategy is beneficial regardless of ovarian response, and to evaluate the possibility of implementing an individualized embryo transfer (iET) based on ovarian response. Methods This was an observational, cohort study performed in a private IVF center. A total of 938 IVF cycles were included in this study. The patients were submitted to controlled ovarian stimulation (COS) with a gonadotropin-releasing hormone (GnRH) antagonist protocol and a cleavage-stage day 3 embryo transfer. We performed a comparison of outcomes between the fresh embryo transfer ( n  = 523) and the freeze-all cycles ( n  = 415). The analysis was performed in two subgroups of patients based on the number of retrieved oocytes: Group 1 (4–9 oocytes) and Group 2 (10–15 oocytes). Result(s) In Group 1 (4–9 retrieved oocytes), the implantation rates (IR) were 17.9 and 20.5% ( P =  0.259 ) in the fresh and freeze-all group, respectively; the ongoing pregnancy rates (OPR) were 31 and 33% ( P  = 0.577) in the fresh and freeze-all group, respectively. In Group 2 (10–15 oocytes), the IR were 22.1 and 30.1% ( P  = 0.028) and the OPR were 34 and 47% ( P  = 0.021) in the fresh and freeze-all groups, respectively. Conclusion(s) Although the freeze-all policy may be related to better in vitro fertilization (IVF) outcomes in normal responders, these potential advantages decrease with worsening ovarian response. Patients with poorer ovarian response do not benefit from the freeze-all strategy.

The freeze-all strategy has emerged as an alternative to fresh embryo transfer (ET) during in vitro fertilization (IVF) cycles. Although fresh ET is the norm during assisted reproductive therapies (ART), there are many concerns about the possible adverse effects of controlled ovarian stimulation (COS) over the endometrium. The supra-physiologic hormonal levels that occur during a conventional COS are associated with modifications in the peri-implantation endometrium, which may be related to a decrease in pregnancy rates and poorer obstetric and perinatal outcomes when comparing fresh to frozen-thawed embryo transfers. The main objective of this study was to assess the available literature regarding the freeze-all strategy in IVF cycles, in regards to effectiveness and safety. Although there are many potential advantages in performing a freeze-all cycle over a fresh ET, it seems that the freeze-all strategy is not designed for all IVF patients. There is a need to develop a non-invasive clinical tool to evaluate the endometrial receptivity during a fresh cycle, which enables the selection of patients that would benefit from this strategy. Today, it is reasonable to perform elective cryopreservation of all oocytes/embryos in cases with a risk of OHSS development, and in patients with supra-physiologic hormonal levels during the follicular phase of COS. It is not clear if all normal responders and poor responders may benefit from this strategy.

Infertility affects 8%-12% of couples worldwide; advanced maternal age combined with diminished ovarian reserve (DOR) significantly lowers IVF success. The flexible GnRH-antagonist and progestin-primed ovarian stimulation (PPOS), are increasingly adopted for freeze-all strategies in this poor-prognosis population; however, their relative effectiveness remains inconclusive. This retrospective study (January 2017-April 2022) enrolled only women ≥ 35 years with diminished ovarian reserve (AMH < 1.2 ng/mL and/or AFC < 5). Two controlled ovarian stimulation protocols were compared: the flexible GnRH-ant protocol and the PPOS protocol. The participants were matched using propensity score matching (PSM) based on age, body mass index (BMI), anti-Müllerian hormone (AMH) level, and antral follicle count (AFC). We compared the ovarian responses to controlled ovarian stimulation treatments and assessed the pregnancy outcomes after FET between the two groups. This study included 141 patients with DOR who underwent the flexible GnRH-ant protocol (  = 58) or PPOS protocol (  = 83). In oocyte retrieval cycles, the flexible GnRH-ant group had higher numbers of retrieved oocytes, MII mature oocytes, normally fertilized oocytes, cleaved embryos, available embryos, and good-quality embryos than the PPOS group (all  < 0.001). However, in FET cycles, the two groups had similar rates of good-quality embryos and clinical outcomes. There were no significant differences between the flexible GnRH-ant protocol and PPOS protocol in clinical pregnancy rate, live birth rate, and chemical pregnancy rate. The implantation rate was also higher in the flexible GnRH-ant protocol (74.5% vs. 60.7%,  < 0.001). Although the quality and quantity of the embryos was different, the good-quality embryo rate and pregnancy outcomes were similar in FET cycles between the flexible GnRH-ant protocol and PPOS protocol in advanced maternal age with DOR.

Purpose To investigate the efficacy of four vaginal progesterones, Lutinus, Utrogestan, Luteum, and Crinone, as luteal phase support (LPS) in frozen‐thawed embryo transfer (Frozen‐ET) cycles. Methods Patients undergoing autologous Frozen‐ET of one cleavage‐stage embryo or one blastocyst. Two hundred fifty‐nine Frozen‐ET cycles were randomized to four groups for LPS: Lutinus, Utrogestan, Luteum, and Crinone. The clinical pregnancy rate (CPR), fetal heartbeat rate (FHR), and miscarriage rate (MR) were analyzed using the Mann‐Whitney or Kruskal‐Wallis test and Fisher exact test. Results Two hundred thirty‐five Frozen‐ET cycles were analyzed: 63 cycles in the Lutinus group, 60 in the Utrogestan group, 56 in the Luteum group, and 56 in the Crinone group. No significant differences were observed between the four groups in CPR (Lutinus, Utrogestan, Luteum, and Crinone: 34.9%, 33.3%, 37.5%, and 35.7%, respectively; P = .976), FHR (26.9%, 31.6%, 30.3%, and 25.0%, respectively; P = .857), and MR (31.8%, 10.0%, 19.0%, and 30.0%, respectively; P = .306). Multivariate logistic regression analysis also revealed that there were no statistically significant differences between the four groups with regard to CPR, FHR, and MR. Conclusion There was no clinically significant difference in pregnancy outcomes between the four vaginal progesterone groups for LPS in Frozen‐ET cycles.

Background Whether menstrual variability in women with regular and ovulatory cycle could affect embryo implantation remains controversial, with conflicting evidences presented in the literature. Thus, in this study, we evaluated the impact of prolonged follicular phase length (FPL) on the clinical pregnancy rate (CPR) after frozen–thawed embryo transfer (FET) in true natural cycles (NC). Methods This retrospective cohort study utilized data from a large university-affiliated reproductive medicine center. Women undergoing true NC-FET were grouped as per their FPL type: Prolonged FPL ( n  = 127) and Normal FPL ( n  = 737). The primary study outcome was CPR in these 2 groups. Results The FPL in the current cycle was significantly longer in the Prolonged FPL group (23.0 ± 2.4) than in the Normal FPL group (16.0 ± 2.2; p  < 0.001). The crude CPR was significantly higher in the Prolonged FPL group (61.4%) than in the Normal FPL group (51.7%; p  = 0.043). After adjusting for the results of potential confounders including the age, BMI, percent of optimal embryos transferred, and endometrial thickness, the difference in the CRP between the 2 groups disappeared (OR 1.28, 95% CI: 0.86–1.91, p  = 0.232). No statistically significant difference was noted in the rates of implantation and miscarriage. Conclusions The current FET should not be cancelled if the ovulation time exceeds the predicted period based on the length of the previous menstrual cycle in the light of no negative effect on the pregnancy outcome.

It is demonstrated that lipid metabolism disorders are associated with the reproductive performances of assisted reproductive technology. However, it is little known whether hyperlipidemia is associated with the endometrial receptivity and pregnancy outcomes of patients undergoing frozen-thawed embryo transfer (FET). This was a retrospective analysis involving 554 infertile women undergoing FET. The patients were divided into the hyperlipidemia group (  = 224) and control group (  = 320) based on the levels of serum lipids. The clinical and laboratory indexes between the two groups were compared. Meanwhile, the stratified analysis based on body mass index (BMI) and endometrial preparation protocols was performed. The independent samples -test, Mann-Whitney test, 2 test and multiple logistic regression analysis were used to compare and analyze the data. The patients with hyperlipidemia had significantly higher serum lipids levels and BMI and lower clinical pregnancy and implantation rates than those with normal blood lipids (  < 0.05). The impact of hyperlipidemia on pregnancy outcomes was independent of BMI. The multiple logistic regression analysis showed that higher cholesterol was associated with lower pregnancy rate and implantation rate (  < 0.05). Regardless of blood lipid levels, the patients undergoing the hormone replacement therapy (HRT) protocol had higher estradiol levels and lower progesterone levels compared with the stimulated cycles (STC) (  < 0.05). Moreover, the clinical pregnancy rate and implantation rate of the HRT protocol were higher than those of the STC, although there was no significant difference between the two. Hyperlipidemia especially higher cholesterol has a negative effect on the pregnancy outcomes of the patients undergoing FET. Actively implementing lipid-lowering treatment and the HRT protocol seem more friendly for these patients.

Purpose To evaluate the outcomes of embryo transfer (ET) and to identify the parameters influencing pregnancy outcomes. Methods This study included 938 ET cycles involving single frozen and thawed good‐quality blastocyst (Gardner grade ≥3BB) between August 2017 and January 2018. The significance of several parameters including endometrial thickness, position of the transferred air bubble, self‐evaluation score by physicians, and uterus direction at ET as predictors of clinical pregnancy was evaluated using univariate and multivariate analyses. Results Among 938 ET cycles, 462 (49.3%) resulted in a clinical pregnancy. Endometrial thickness was positively associated with clinical pregnancy in a linear trend. Between the variable position of the transferred air bubble and clinical pregnancy rate showed a curvilinear relationship. Clinical pregnancy rate was higher in cases with good self‐evaluation score, whereas there was no difference between groups with different uterus directions. Univariate analysis of predictive parameters identified endometrial thickness, self‐evaluation score by physicians, and position of air bubbles as significant predictors of clinical pregnancy, of which endometrial thickness and position of air bubbles appeared to be independently related to clinical pregnancy. Conclusion Endometrial thickness and the position of transferred air bubbles influenced clinical pregnancy in ET cycles.

Purpose Previous studies have reported different methods of estrogen administration during endometrial preparation for frozen‐thawed embryo transfer (FET). This study aimed to investigate a beneficial regimen of transdermal estrogen administration for FET. Methods We investigated the reproductive and obstetric outcomes of FET by comparing the increasing dose (ID) group that mimics changes in serum estradiol during the menstrual cycle and the constant dose (CD) group. Transdermal patches were used for estrogen administration in both groups. In our hospital, we targeted 315 cycles of the ID group in which FET was performed in 2017 and 324 cycles of the CD group in which FET was performed in 2018. In all cases, single embryo transfer was performed. Results All were singleton pregnancies. There was no difference in clinical pregnancy rate (28.9% vs 28.2%, P =.837) and live birth rate (17.3% vs 21.4%, P =.201) between the ID and CD groups. Spontaneous abortion rate was significantly lower in the CD group than in the ID group (37.2% vs 23.0%, P =.041). There was no difference in obstetrical outcomes. Conclusions It was considered that the simple CD regimen may be more beneficial than the complicated ID regimen.

Purpose To demonstrate the benefits of the freeze‐all strategy for in vitro fertilization treatment based on retrospective analyses. Methods Post‐thaw embryo survival rates of slow‐frozen embryos in 294 cycles and vitrified embryos in 12 195 cycles were assessed. Progesterone (P4) and estradiol (E2) levels per mature oocyte by age category were assessed in 9081 cycles and pregnancy rates with fresh embryo transfer and frozen‐thawed embryo transfer by P4 level were assessed in 1535 cycles. Results The survival rates of frozen‐thawed embryos were 92.5% with slow freezing and 99.1% with vitrification. P4 levels on the day of human chorionic gonadotropin (hCG) injection showed a trend toward an increase with age. The pregnancy rate per mature oocyte with fresh embryo transfer decreased dependently upon P4 level, while that with frozen‐thawed embryo transfer was not affected by P4 level. The pregnancy rates with frozen‐thawed embryo transfer were higher than those with fresh embryo transfer in patients aged 42 years or younger. Conclusions The freeze‐all strategy is a valuable treatment option which allows the separation of an embryo transfer cycle from an oocyte retrieval cycle, especially for patients with high P4 levels at oocyte retrieval and patients of advanced maternal age.