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Objective To investigate the predictive value of endometrial thickness (EMT) for live birth when a lower threshold of EMT is not employed for embryo transfer (ET). Design Retrospective study Setting Academic assisted reproduction center Patient(s) All women who underwent fresh or frozen-thawed ET at the Koc University Hospital Assisted Reproduction Unit between October 2016 and August 2019 Intervention(s) After ruling out endometrial pathology, blastocyst transfer was planned regardless of the EMT in the absence of increased serum progesterone level on the trigger day in fresh embryo transfer cycles or before commencing progesterone treatment in artificially prepared frozen-thawed ET cycles. Main Outcome Measure(s) The primary outcome was live birth. Live birth and miscarriage rates per ET were stratified according to fresh and frozen-thawed ET cycles for each millimeter of endometrial thickness. Receiver operator characteristic curve analyses were performed to evaluate the predictive value of EMT for live birth. Result(s) A total of 560 ET cycles, 273 fresh and 287 frozen-thawed, were included in the study. Relevant patient characteristics as well as EMTs were similar between women who achieved a live birth and those who did not after fresh or frozen-thawed ET. There was no linear association between EMT and live birth or miscarriage rates. Area under the curve values for EMT to predict live birth after fresh, frozen-thawed, and all ETs were 0.56, 0.47, and 0.52, respectively. Conclusion(s) Our results showed that the EMT was not predictive for live birth in either fresh or frozen-thawed ET cycles. Once intracavitary pathology and inadvertent progesterone exposure were excluded, women with thinner EMTs should not be denied their potential for live birth because it is comparable to that of those with thicker EMT.

Research question Does subcutaneous progesterone provide similar live birth or ongoing pregnancy rates as vaginal progesterone in frozen embryo transfer (FET) cycles? Design Retrospective cohort study (n = 214 women), consisting of 107 women who received subcutaneous progesterone for FET in artificial cycles and 107 women receiving vaginal progesterone who were matched for age and treatment cycle rank acted as controls. All embryos were transferred in an artificial cycle with 6 mg per day oral oestradiol valerate starting on the second or third day of the menstrual cycle. Patients underwent transvaginal ultrasound on the 10th day of priming, and subcutaneous progesterone (50 mg/day) or vaginal progesterone (180 mg/day) was started if the endometrium had a trilinear pattern regardless of its thickness. Embryo transfer was carried out on the sixth day of progesterone administration. Oestradiol and progesterone were continued until a negative pregnancy test, 10 days after the transfer, or until the completion of 10th gestational week. Main outcome measures were live birth or ongoing pregnancy rates. Results Baseline characteristics were similar between the groups. Positive pregnancy test rates (64.5% versus 58.9%; P = 0.40; RR 1.1; 95% CI 0.89 to 1.35), live birth or ongoing pregnancy rates (39.3% versus 35.5%; P = 0.57; RR 1.11; 95% CI 0.78 to 1.56) and miscarriage rates (29% versus 25.5%; P = 0.68; RR 1.08; 95% CI 0.76 to 1.55) were similar in the subcutaneous progesterone and vaginal progesterone groups, respectively. Conclusions Subcutaneous progesterone seems to be an effective alternative to vaginal progesterone in patients undergoing FET. Randomized controlled trials comparing it with different progesterone preparations, routes and protocols are needed to better define its role.

Research question Do live birth rates (LBR), obstetric and perinatal outcomes vary between women who underwent frozen embryo transfer (ET) in the immediately subsequent menstrual cycle, and with those who underwent delayed frozen ET. Design Retrospective cohort study (n = 198) consisting of 119 women who underwent immediate transfer within 30 days of oocyte retrieval (OR) and 79 women who underwent delayed transfer which was performed after >30 days following OR. Either flexible antagonist or flexible progestin-primed ovarian stimulation protocols were started after a baseline ultrasonography on the second or third day of menstrual cycle. Only freeze all cycles were included in the study and all transfers were with hormonal endometrial preparation. Main outcome measures were LBR, birth weight, gestational day at birth and pregnancy complications. Results Peak estradiol level on trigger day (2746 vs 2081 pg/ml) and number of metaphase-two oocytes (13 vs 10) were significantly higher in the immediate transfer group. Clinical pregnancy rate per ET was similar between the groups (50.4% vs 44.3%). However, miscarriage rate per positive pregnancy was significantly higher (12.3% vs 31.1%) while LBR per ET was significantly lower (42.9% vs 26.6%) in the delayed transfer group. Median gestational age at delivery were 267.5 and 268 days in the immediate and delayed transfer groups. Median birthweight was significantly higher in the delayed transfer group (3520 vs 3195 g). Adjusted analyses also suggest similar LBR with immediate and delayed transfer. Conclusion(s) Frozen ET in the immediate menstrual cycle and delayed ET, after a freeze all strategy did not show significant difference in terms of LBR after adjustment. Obstetric and perinatal outcomes of frozen ET in the immediate menstrual cycle appear reassuring.