Association between the length of in vitro embryo culture, mode of ART, and the initial endogenous hCG rise in ongoing singleton pregnancies.

STUDY QUESTION: Is there an association between the length of in vitro culture, mode of ART and the initial endogenous hCG rise, in cycles with a foetal heartbeat after single embryo transfer (ET) and implantation? SUMMARY ANSWER: Both the length of in vitro culture and the mode of ART have an impact on the initial endogenous rise in hCG in singleton pregnancies. WHAT IS KNOWN ALREADY: Different factors have been identified to alter the kinetics of hCG in pregnancies. Current studies show conflicting results regarding the kinetics of hCG after different types of ART (fresh vs frozen ET (FET)), the inclusion or not of preimplantation genetic testing (PGT), and the length of time in in vitro culture. STUDY DESIGN, SIZE, DURATION: This was a multicentre cohort study, using prospectively collected data derived from 4938 women (5524 treatment cycles) undergoing IUI (cycles, n = 608) or ART (cycles, n = 4916) treatments, resulting a in singleton ongoing pregnancy verified by first-trimester ultrasound scan. Data were collected from the Danish Medical Data Centre, used by the three participating Danish public fertility clinics at Copenhagen University hospitals: Herlev Hospital, Hvidovre Hospital, and Rigshospitalet, from January 2014 to December 2021. PARTICIPANTS/MATERIALS, SETTING, METHODS: The fresh ET cycles included cleavage-stage (2 or 3 days in vitro) and blastocyst (5 days in vitro) transfers. FET cycles included cleavage-stage (3 days in vitro before cryopreservation) or blastocyst (5 or 6 days in vitro before cryopreservation) transfers. The IUI cycles represented no time in vitro. To attain a comparable interval for serum-hCG (s-hCG), the ovulation induction time was identical: 35-37 h before oocyte retrieval or IUI. The conception day was considered as: the insemination day for pregnancies conceived after IUI, the oocyte retrieval day for fresh ET, or the transfer day minus 3 or 5 as appropriate for FET of Day 3 or 5 embryos. Multiple linear regression analysis was used, including days post-conception for the hCG measurement as a covariate, and was adjusted for the women's age, the cause of infertility, and the centre. For FET, a sensitivity analysis was used to adjust for endometrial preparation. MAIN RESULTS AND THE ROLE OF CHANCE: The study totally includes 5524 cycles: 2395 FET cycles, 2521 fresh ET cycles, and 608 IUI cycles. Regarding the length of in vitro culture, with IUI as reference (for no time in in vitro culture), we found a significantly lower s-hCG in pregnancies achieved after fresh ET (cleavage-stage ET or blastocyst transfer). S-hCG was 18% (95% CI: 13-23%, P < 0.001) lower after fresh cleavage-stage ET, and 23% (95% CI: 18-28%, P < 0.001) lower after fresh blastocyst transfer compared to IUI. In FET cycles, s-hCG was significantly higher after blastocyst transfers compared to cleavage-stage FET, respectively, 26% (95% CI: 13-40%, P < 0.001) higher when cryopreserved on in vitro Day 5, and 14% (95% CI: 2-26%, P = 0.02) higher when cryopreserved on in vitro Day 6 as compared to Day 3. Regarding the ART treatment type, s-hCG after FET blastocyst transfer (Day 5 blastocysts) cycles was significantly higher, 33% (95% CI: 27-45%, P < 0.001), compared to fresh ET (Day 5 blastocyst), while there was no difference between cleavage-stage FET (Days 2 + 3) and fresh ET (Days 2 + 3). S-hCG was 12% (95% CI: 4-19%, 0.005) lower in PGT FET (Day 5 blastocysts) cycles as compared to FET cycles without PGT (Day 5 blastocysts). LIMITATIONS, REASONS FOR CAUTION: The retrospective design is a limitation which introduces the risk of possible bias and confounders such as embryo score, parity, and ovarian stimulation. WIDER IMPLICATIONS OF THE FINDINGS: This study elucidates how practices in medically assisted reproduction treatment are associated with the hCG kinetics, underlining a potential impact of in vitro culture length and mode of ART on the very early embryo development and implantation. The study provides clinicians knowledge that the type of ART used may be relevant to take into account when evaluating s-hCG for the prognosis of the pregnancy. STUDY FUNDING/COMPETING INTEREST(S): No funding was received for this study. AP has received consulting fees, research grants, or honoraria from the following companies: Preglem, Novo Nordisk, Ferring Pharmaceuticals, Gedeon Richter, Cryos, Merck A/S, and Organon. AZ has received grants and honoraria from Gedeon Richter. NLF has received grants from Gedeon Richter, Merck A/S, and Cryos. MLG has received honoraria fees or research grants from Gedeon Richter, Merck A/S, and Cooper Surgical. CB has received honoraria from Merck A/S. MB has received research grants and honoraria from IBSA. MPR, KM, and PVS all report no conflicts of interest. TRIAL REGISTRATION NUMBER: The study was registered and approved by the Danish Protection Agency, Capital Region, Denmark (Journal-nr.: 21019857). No approval was required from the regional ethics committee according to Danish law.

Developmental stage and morphology of the competent blastocyst are associated with sex of the child but not with other obstetric outcomes: a multicenter cohort study.

STUDY QUESTION: Are transfer day, developmental stage and morphology of the competent blastocyst in pregnancies leading to live birth associated with preterm birth, birthweight, length at birth and sex of the child? SUMMARY ANSWER: A high score in blastocyst developmental stage and in trophectoderm (TE) showed a significant association with the sex of the child, while no other associations with obstetric outcomes were observed. WHAT IS KNOWN ALREADY: The association between blastocyst assessment scores and obstetric outcomes have been reported in small single-center studies and the results are conflicting. STUDY DESIGN, SIZE, DURATION: Multicenter historical cohort study based on exposure data (transfer day (blastocyst developmental stage reached by Day 5 or Day 6)) blastocyst developmental stage (1-6) and morphology (TE and inner cell mass (ICM): A, B, C)) and outcome data (preterm birth, birthweight, length at birth, and sex of the child) from women undergoing single blastocyst transfer resulting in a singleton pregnancy and live birth. PARTICIPANTS/MATERIALS, SETTING, METHODS: Data from 16 private and university-based facilities for clinical services and research were used. A total of 7246 women, who in 2014-2018 underwent fresh-embryo transfer with a single blastocyst or frozen-thawed embryo transfer (FET) with a single blastocyst resulting in a singleton pregnancy were identified. Linking to the Danish Medical Birth Registry resulted in a total of 4842 women with a live birth being included. Cycles with pre-implantation genetic testing and donated gametes were excluded. The analyses were adjusted for female age (n = 4842), female BMI (n = 4302), female smoking (n = 4290), parity (n = 4365), infertility diagnosis (n = 4765), type of treatment (n = 4842) and center (n = 4842); some analyses additionally included gestational age (n = 4368) and sex of the child (n = 4833). MAIN RESULTS AND THE ROLE OF CHANCE: No statistically significant associations between blastocyst assessment scores (transfer day, developmental stage, TE, ICM) and preterm birth (8.3%) or birthweight (mean 3461.7 g) were found. The adjusted association between blastocysts with a TE score of C and a TE score of A and length at birth (mean 51.6 cm) were statistically significant (adjusted mean difference 0.4 cm (95% CI: 0.02; 0.77)). Blastocysts transferred with developmental stage score 5 compared to blastocysts transferred with score 3 had a 34% increased probability of being a boy (odds ratio (OR) 1.34 (95% CI: 1.09; 1.64). Further, TE score B blastocysts compared to TE score A blastocysts had a 31% reduced probability of being a boy (OR 0.69 (95% CI: 0.60; 0.80)). LIMITATIONS, REASONS FOR CAUTION: It is possible that some residual confounding remains. WIDER IMPLICATIONS OF THE FINDINGS: Blastocyst selection during ART does not appear to introduce any negative effects on obstetric outcome. Therefore, clinicians and patients can be reassured that the assessment scores of the selected blastocyst will not in themselves pose a risk of preterm birth or affect birthweight and the length at birth. STUDY FUNDING/COMPETING INTEREST(S): Unrestricted grant from Gedeon Richter Nordics AB, Sweden. None of the authors have any competing interest to declare. TRIAL REGISTRATION NUMBER: N/A.