ESHRE guideline: number of embryos to transfer during IVF/ICSI†.

STUDY QUESTION: Which clinical and embryological factors should be considered to apply double embryo transfer (DET) instead of elective single embryo transfer (eSET)? SUMMARY ANSWER: No clinical or embryological factor per se justifies a recommendation of DET instead of eSET in IVF/ICSI. WHAT IS KNOWN ALREADY: DET is correlated with a higher rate of multiple pregnancy, leading to a subsequent increase in complications for both mother and babies. These complications include preterm birth, low birthweight, and other perinatal adverse outcomes. To mitigate the risks associated with multiple pregnancy, eSET is recommended by international and national professional organizations as the preferred approach in ART. STUDY DESIGN, SIZE, DURATION: The guideline was developed according to the structured methodology for development and update of ESHRE guidelines. Literature searches were performed in PUBMED/MEDLINE and Cochrane databases, and relevant papers published up to May 2023, written in English, were included. Live birth rate, cumulative live birth rate, and multiple pregnancy rate were considered as critical outcomes. PARTICIPANTS/MATERIALS, SETTING, METHODS: Based on the collected evidence, recommendations were discussed until a consensus was reached within the Guideline Development Group (GDG). A stakeholder review was organized after the guideline draft was finalized. The final version was approved by the GDG and the ESHRE Executive Committee. MAIN RESULTS AND THE ROLE OF CHANCE: The guideline provides 35 recommendations on the medical and non-medical risks associated with multiple pregnancies and on the clinical and embryological factors to be considered when deciding on the number of embryos to transfer. These recommendations include 25 evidence-based recommendations, of which 24 were formulated as strong recommendations and one as conditional, and 10 good practice points. Of the evidence-based recommendations, seven (28%) were supported by moderate-quality evidence. The remaining recommendations were supported by low (three recommendations; 12%), or very low-quality evidence (15 recommendations; 60%). Owing to the lack of evidence-based research, the guideline also clearly mentions recommendations for future studies. LIMITATIONS, REASONS FOR CAUTION: The guideline assessed different factors one by one based on existing evidence. However, in real life, clinicians' decisions are based on several prognostic factors related to each patient's case. Furthermore, the evidence from randomized controlled trials is too scarce to formulate high-quality evidence-based recommendations. WIDER IMPLICATIONS OF THE FINDINGS: The guideline provides health professionals with clear advice on best practice in the decision-making process during IVF/ICSI, based on the best evidence currently available, and recommendations on relevant information that should be communicated to patients. In addition, a list of research recommendations is provided to stimulate further studies in the field. STUDY FUNDING/COMPETING INTEREST(S): The guideline was developed and funded by ESHRE, covering expenses associated with the guideline meetings, the literature searches, and the dissemination of the guideline. The guideline group members did not receive payment. DPB declared receiving honoraria for lectures from Merck, Ferring, and Gedeon Richter. She is a member of ESHRE EXCO, and the Mediterranean Society for reproductive medicine and the president of the Croatian Society for Gynaecological Endocrinology and Reproductive Medicine. CDG is the past Chair of the ESHRE EIM Consortium and a paid deputy member of the Editorial board of Human Reproduction. IR declared receiving reimbursement from ESHRE and EDCD for attending meetings. She holds an unpaid leadership role in OBBCSSR, ECDC Sohonet, and AER. KAR-W declared receiving grants for clinical researchers and funding provision to the institution from the Swedish Cancer Society (200170F), the Senior Clinical Investigator Award, Radiumhemmets Forskningsfonder (Dnr: 201313), Stockholm County Council FoU (FoUI-953912) and Karolinska Institutet (Dnr 2020-01963), NovoNordisk, Merck and Ferring Pharmaceuticals. She received consulting fees from the Swedish Ministry of Health and Welfare. She received honoraria from Roche, Pfizer, and Organon for chairmanship and lectures. She received support from Organon for attending meetings. She participated in advisory boards for Merck, Nordic countries, and Ferring. She declared receiving time-lapse equipment and grants with payment to institution for pre-clinical research from Merck pharmaceuticals and from Ferring. SS-R received research funding from Roche Diagnostics, Organon/MSD, Theramex, and Gedeo-Richter. He received consulting fees from Organon/MSD, Ferring Pharmaceuticals, and Merck Serono. He declared receiving honoraria for lectures from Ferring Pharmaceuticals, Besins, Organon/MSD, Theramex, and Gedeon Richter. He received support for attending Gedeon Richter meetings and participated in the Data Safety Monitoring Board of the T-TRANSPORT trial. He is the Deputy of ESHRE SQART special interest group. He holds stock options in IVI Lisboa and received equipment and other services from Roche Diagnostics and Ferring Pharmaceuticals. KT declared receiving payment for honoraria for giving lectures from Merck Serono and Organon. She is member of the safety advisory board of EDQM. She holds a leadership role in the ICCBBA board of directors. ZV received reimbursement from ESHRE for attending meetings. She also received research grants from ESHRE and Juhani Aaltonen Foundation. She is the coordinator of EHSRE SQART special interest group. The other authors have no conflicts of interest to declare. DISCLAIMER: This guideline represents the views of ESHRE, which were achieved after careful consideration of the scientific evidence available at the time of preparation. In the absence of scientific evidence on certain aspects, a consensus between the relevant ESHRE stakeholders has been obtained. Adherence to these clinical practice guidelines does not guarantee a successful or specific outcome, nor does it establish a standard of care. Clinical practice guidelines do not replace the need for application of clinical judgement to each individual presentation, nor variations based on locality and facility type. ESHRE makes no warranty, express or implied, regarding the clinical practice guidelines and specifically excludes any warranties of merchantability and fitness for a particular use or purpose (full disclaimer available at https://www.eshre.eu/Guidelines-and-Legal).

Beyond the microscope: the importance of leadership skills in IVF laboratory management.

In healthcare, leadership plays a crucial role in determining the quality of care and overall clinical performance. However, the pivotal role of leadership in the effective functioning and success of IVF laboratories is often overlooked. This commentary seeks to address this gap. It is necessary to explore the multifaceted nature of an IVF laboratory director's role, as well as the need for a new approach to IVF laboratory management that strongly emphasizes the cultivation of leadership skills in tandem with technical expertise. By enhancing leadership skills, IVF laboratories can improve their efficiency, team morale and patient outcomes.

Shedding light on the ART laboratory.

This commentary examines the impact of light conditions in the assisted reproductive technology (ART) laboratory, specifically considering gametes and embryo culture. While these processes traditionally occur in the absence of light within the female reproductive tract, laboratory conditions often involve exposure to varying wavelengths, intensities and light sources. Although literature reports describe potential detrimental effects of certain wavelengths of light on biological material, these findings are often based on experiments that might not reflect actual laboratory conditions. Current ART laboratory practices aim to minimize light exposure; however, some procedures necessitate light exposure, typically involving microscopy. Results from the authors' cross-sectional survey on light-intensity practices in ART laboratories revealed the frequent use of inadequate lighting, leading to errors and impacting staff well-being. A failure mode and effects analysis was used to identify potential failure modes and their impacts due to poor lighting. Overall, this manuscript stresses the importance of maintaining proper ambient lighting in the ART laboratory, balancing the potentially detrimental effects of light on gametes and embryos against the need for proper lighting for accurate procedures and staff well-being. Adequate lighting not only ensures the safety of reproductive cells, but also improves process management and the operators' psychological conditions.

Sustainability in the IVF laboratory: recommendations of an expert panel.

The healthcare industry is a major contributor to greenhouse gas emissions. Assisted reproductive technology is part of the larger healthcare sector, with its own heavy carbon footprint. The social, economic and environmental costs of this collective carbon footprint are becoming clearer, as is the impact on human reproductive health. Alpha Scientists in Reproductive Medicine and the International IVF Initiative collaborated to seek and formulate practical recommendations for sustainability in IVF laboratories. An international panel of experts, enthusiasts and professionals in reproductive medicine, environmental science, architecture, biorepository and law convened to discuss the topics of importance to sustainability. Recommendations were issued on how to build a culture of sustainability in the workplace, implement green design and building, use life cycle analysis to determine the environmental impact, manage cryostorage more sustainably, and understand and manage laboratory waste with prevention as a primary goal. The panel explored whether the industry supporting IVF is sustainable. An example is provided to illustrate the application of green principles to an IVF laboratory through a certification programme. The UK legislative landscape surrounding sustainability is also discussed and a few recommendations on 'Green Conferencing' are offered.

Preterm birth in singleton pregnancies conceived by in vitro fertilization or intracytoplasmic sperm injection: an overview of systematic reviews.

BACKGROUND: The rate of preterm birth of singletons conceived through in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) is increased, being as high as 15% to 16% across Europe and the United States. However, the underlying etiology, phenotype, and mechanisms initiating preterm birth (PTB) are poorly understood. OBJECTIVE: To quantify the PTB risk and examine supposed etiology in IVF/ICSI singleton pregnancies compared to naturally conceived. STUDY DESIGN: Overview of reviews including all available systematic reviews with meta-analysis comparing PTB risk in IVF/ICSI and naturally conceived singletons. A comprehensive search of PubMed/MEDLINE, Embase, Scopus, and Cochrane Library databases was performed up to December 31, 2023. Information available on etiology, phenotype, initiation of PTB, and relevant moderators was retrieved and employed for subgroup analyses. Random-effects meta-analysis models were used for pooling effect measures. Estimates were presented as odds ratios (ORs) with 95% confidence intervals (CIs). The extent of overlap in the original studies was measured using the corrected covered area assessment. The quality of the included reviews was evaluated with the AMSTAR 2 tool. The Grading of Recommendations Assessment, Development and Evaluation approach was applied to rate evidence certainty. The protocol was registered on PROspective Register of Systematic Reviews (CRD42023411418). RESULTS: Twelve meta-analyses (16,522,917 pregnancies; ˃433,330 IVF/ICSI) were included. IVF/ICSI singletons showed a significantly higher PTB risk compared to natural conception (PTB ˂37 weeks: OR: 1.72, 95% CI: 1.57-1.89; PTB<32 weeks: OR: 2.19, 95% CI: 1.82-2.64). Influential analysis reinforced the strength of this association. Subgroup analyses investigating supposed etiology revealed a comparable risk magnitude for spontaneous PTB (OR: 1.79, 95% CI: 1.56-2.04) and a greater risk for iatrogenic PTB (OR: 2.28, 95% CI: 1.72-3.02). PTB risk was consistent in the subgroup of conventional IVF (OR: 1.95, 95% CI: 1.76-2.15) and higher in the subgroup of fresh only (OR: 1.79, 95% CI: 1.55-2.07) vs frozen-thawed embryo transfers (OR: 1.39, 95% CI: 1.34-1.43). There was minimal study overlap (13%). The certainty of the evidence was graded as low to very low. CONCLUSION: Singletons conceived through IVF/ICSI have a 2-fold increased risk of PTB compared to natural conception, despite the low certainty of the evidence. There is paucity of available data on PTB etiology, phenotype, or initiation. The greater risk increase is observed in fresh embryo transfers and involves iatrogenic PTB and PTB ˂32 weeks, likely attributable to placental etiology. Future studies should collect data on PTB etiology, phenotype, and initiation. IVF/ICSI pregnancies should undertake specialistic care with early screening for placental disorders, cervical length, and growth abnormalities, allowing appropriate timely follow-up, preventive measures, and therapeutic interventions strategies.

When the Embryo Meets the Endometrium: Identifying the Features Required for Successful Embryo Implantation.

Evaluation of the optimal number of embryos, their quality, and the precise timing for transfer are critical determinants in reproductive success, although still remaining one of the main challenges in assisted reproduction technologies (ART). Indeed, the success of in vitro fertilization (IVF) treatments relies on a multitude of events and factors involving both the endometrium and the embryo. Despite concerted efforts on both fronts, the overall success rates of IVF techniques continue to range between 25% and 30%. The role of the endometrium in implantation has been recently recognized, leading to the hypothesis that both the "soil" and the "seed" play a central role in a successful pregnancy. In this respect, identification of the molecular signature of endometrial receptivity together with the selection of the best embryo for transfer become crucial in ART. Currently, efforts have been made to develop accurate, predictive, and personalized tests to identify the window of implantation and the best quality embryo. However, the value of these tests is still debated, as conflicting results are reported in the literature. The purpose of this review is to summarize and critically report the available criteria to optimize the success of embryo transfer and to better understand current limitations and potential areas for improvement.

Delayed blastocyst development is influenced by the level of progesterone on the day of trigger.

PURPOSE: To evaluate the association between progesterone (P) level on the day of trigger and time to blastulation in IVF cycles. METHODS: This was a retrospective cohort study with autologous IVF cycles performed at our Institution from January 2019 to December 2021. A total of 1109 IVF cycles were included. The primary outcome was to compare time to blastulation in terms of percentage of expanded (grade 3) blastocysts on day 5 according to progesterone level at trigger. RESULTS: A total of 3517 blastocysts were analyzed. After dividing progesterone level in quartiles (Q1, P < 0.50 ng/ml; Q2 0.50 ng/ml ≤ P ≤ 0.78 ng/ml; Q3, 0.79 ng/ml ≤ P ≤ 1.15 ng/ml; Q4, P > 1.15 ng/ml), we observed a delay in blastocyst development according to the increasing level of progesterone at trigger (analysis by rank, P-value = 0.01). After adjusting for confounding factors at the multivariate analysis, the percentage of day 5 blastocysts was reduced for Q3 (- 13.8%, 95% CI from - 20.5 to - 7.0%, p < 0.001) and Q4 (- 7.7%, 95% CI from - 15.5 to 0.0%, p = 0.05) compared to Q1 (reference). CONCLUSIONS: Progesterone levels on day of trigger correlate to the percentage of expanded (grade 3) blastocysts on day 5 and a delayed blastocyst development day 5 is expected for high progesterone levels.

Progesterone levels during ovarian stimulation in segmented ART cycles inversely correlate with normalized birthweight of neonates conceived through subsequent frozen-thawed embryo transfer.

PURPOSE: To evaluate the association between serum progesterone (P) at the day of ovulation trigger and neonatal birthweight in singletons born after frozen-thawed embryo transfer in segmented ART cycles. METHODS: A retrospective multicenter cohort study involving data from patients who achieved uncomplicated pregnancy and term delivery of ART-conceived singleton babies following a segmented GnRH antagonist cycle. The main outcome was birthweight's z-score of the neonate. Univariate and multivariate linear logistic regression analyses were made to investigate the relation of z-score with variables inherent to the patient and to the ovarian stimulation. The variable P per oocyte was created by dividing the value of progesterone at ovulation trigger by the number of oocytes retrieved at oocyte retrieval. RESULTS: A total of 368 patients were included in the analysis. At univariate linear regression, the birthweight z-score of the neonate appeared to be inversely related to both P levels at the ovulation trigger (- 0.101, p = 0.015) and P levels per oocyte at trigger (- 1.417, p = 0.001), while it was directly related to the height of the mother (0.026, p = 0.002) and to the number of previous live births (0.291, p = 0.016). In multivariate analysis, both serum P (- 0.1; p = 0.015) and P per oocyte (- 1.347, p = 0.002) maintained the significant inverse association with birthweight z-score after adjusting for height and parity. CONCLUSIONS: Serum progesterone level on the day of ovulation trigger inversely correlates with normalized birthweight of neonates in segmented GnRH antagonist ART cycles.

The effect of vitrified-warmed blastocyst transfer on postnatal growth: a 1-year follow-up questionnaire study.

RESEARCH QUESTION: Is postnatal growth of singletons aged 12 months born after vitrified-warmed blastocyst transfer (frozen embryo transfer [FET]) different from children born after fresh blastocyst transfer? DESIGN: A retrospective cohort study conducted at a single university-affiliated obstetrics and fertility centre between 2014 and 2016. Women who underwent fresh transfer or FET at blastocyst stage and obtained a singleton live birth were included. Propensity score inverse probability weighting was used to balance baseline maternal characteristics between fresh and FET cycles. RESULTS: Of the 382 women with singleton live births, 124 underwent a fresh blastocyst transfer and 258 underwent a FET. Significantly higher birth weight and length z-scores were observed after FET (P = 0.01 and P = 0.002, respectively) compared with the fresh transfer group. At 12 months of age, the fresh and FET groups showed no significant effect on the weight z-score, but the FET was associated with a higher height z-score (P = 0.001) compared with fresh blastocyst transfer. The comparison between males and females from the same study group showed higher birth weight z-score for males in the FET group (P < 0.001). During the first 12 months, however, males in the FET group showed a slower growth trajectory in terms of weight (P = 0.007). CONCLUSIONS: At 12 months of postnatal life, an increased height and sex-dependent differences in growth trajectories were observed in singletons born after FET compared with those born after fresh embryo transfer.

Learning from incidents in medically assisted reproduction: the Notify Library as a learning tool.

Biovigilance is the systematic monitoring of serious adverse reactions and events (SARE) that ensures the quality and safety of tissues and cells for human application in medically assisted reproduction (MAR). The Notify Library is an open access database launched by the World Health Organization and supported by the Italian National Transplant Centre (CNT) that has collected information on documented adverse occurrences in transplantation, transfusion and MAR. It is not a SARE register, but rather a collection of SARE types identified primarily by review of published articles and case reports from national or regional vigilance programmes. The Notify Library includes many well-documented records of adverse occurrences in MAR treatment, representing a useful tool for MAR operators in the evaluation of the risks associated with the clinical application of reproductive tissues and cells. It is updated with new records when a new type of incident is reported for the first time. All incident types described might have teaching value during the risk management carried out by a MAR centre. Sharing lessons learned from these incidents represents an important didactic opportunity that can help MAR centres to improve their processes and to achieve higher standards of quality and safety.

Cryopreservation in reproductive medicine during the COVID-19 pandemic: rethinking policies and European safety regulations.

Cryopreservation of reproductive cells and tissues represents an essential aspect of ART practices that might be particularly strategic and helpful during severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emergency. However, recommendations on how and when to preserve reproductive tissues and cells during a novel severe pandemic are scanty. This article uses a SWOT (strengths, weaknesses, opportunities and threats) analysis to identify favourable and unfavourable factors and to recognize challenges and obstacles related to the use of cryopreservation procedures during the spreading of a new virus. One of the strengths associated with the cryopreservation is represented by the availability of robust European guidelines on storage safety to prevent sample contamination or cross-contamination by pathogens. These recommendations should be deep-rooted in all ART laboratories. Weaknesses include uncertainties regarding the management of COVID-19 affected asymptomatic patients, the suboptimal accuracy of diagnostic tests for the disease, the nebulous prospective regarding the duration of the pandemic and the additional costs. The application of the strategy represents an opportunity to postpone pregnancy in order to avoid a severe infectious disease during gestation while concomitantly counteracting the possible detrimental effect of time. Critical threats, at present still undefined, are represented by potential adverse events for the mother and offspring due to infected gametes or embryos after thawing and, subsequently, the re-spreading of the virus.

Shooting STAR: reinterpreting the data from the 'Single Embryo TrAnsfeR of Euploid Embryo' randomized clinical trial.

Preimplantation genetic testing for aneuploidy (PGT-A) still remains controversial in clinical practice. Recently, the randomized controlled trial, 'Single Embryo TrAnsfeR of Euploid Embryo' (STAR) by Munné and coworkers showed a similar live birth rate per intention to treat in the two study groups (PGT-A and controls). A wrong diagnosis and/or biopsy-related damage to the embryo might underlie these results. To assess the impact of these factors on the efficiency of PGT-A, the live birth rate of 'euploid' embryos transferred in the PGT-A group was compared with its ideal value, namely the live birth rate of embryos with the potential to implant and to give rise to a baby in the control group. This estimate has been derived using the results of the genetic testing reported in the STAR trial. According to this model, the STAR trial has demonstrated that transferring only blastocysts classified as 'euploid' after PGT-A leads to a reduction from 82.2% to 50.0% of the live birth rate for competent embryos, thus supporting the idea that PGT-A is associated with some embryo wastage.

Assessment of pre-implantation genetic testing for embryo aneuploidies: A SWOT analysis.

The recently re-named pre-implantation genetic testing for determining embryo aneuploidies (PGT-A) is presently very popular although its acceptance by the scientific community is controversial. This approach still encounters drawbacks. This paper uses a SWOT (strengths, weaknesses, opportunities and threats) analysis to discuss salient points to be considered when examining the pre-implantation genetic testing (PGT-A) strategy to gather information from a range of perspectives. One of the strengths associated with the procedure is represented by an increase in implantation rate although data from the highest level of evidence do not support an increase in cumulative pregnancy rates. The current difficulty in the management of mosaicisms represents a weakness of PGT-A. The application of the strategy represents an opportunity to favor the single embryo transfer while other advantages, such as reduction of time to pregnancy and emotional distress are controversial. Potential important threats, at present still undefined, are represented by the biopsy-related damage to the blastocyst and the impact on neonatal and long-term outcomes.

Elective egg freezing without medical indications.

The aim of this review is to provide current knowledge on fertility preservation for non-medical reasons in women willing to postpone childbearing. The topic is highly debatable, starting from disagreement about its terminology, the number of eggs necessary to predict chances of success, and the safety and socio/ethical point of view. Cost analysis and discrepancies among countries' recommendations and regulations are described to confirm the controversies and unsolved issues around this very interesting topic. Finally, an overview on the returning rate of women among "egg bankers" and reasons behind their decisions are illustrated.

Revisiting embryo assisted hatching approaches: a systematic review of the current protocols.

Zona pellucida (ZP) manipulation, termed "assisted hatching" (AH), has been introduced in order to favor embryo hatching and ultimately improve assisted reproductive technology success but with poor proofs of safety and biological plausibility. We herein provide a systematic review of clinical outcomes following the application of different methods of ZP manipulation on fresh or frozen/thawed embryos at different developmental stages in different groups of patients. Out of the 69 papers that compared the clinical outcomes deriving from hatched versus non-hatched embryos, only 11 considered blastocysts while the rest referred to cleavage stage embryos. The ZP thinning of fresh embryos either by chemical or laser approach was shown to provide very limited benefit in terms of clinical outcomes. Better results were observed with procedures implying a higher degree of zona manipulation, including zona removal. Studies comparing the mechanical or chemical procedures to those laser-mediated consistently reported a superiority of the latter ones over the former. Literature is consistent for a benefit of ZP breaching in thawed blastocysts. This review provides the current knowledge on the AH procedure in order to improve its efficacy in the appropriate context. Embryologists might benefit from the approaches presented herein in order to improve Assisted Reproduction Technologies (ART) outcomes.

Vitamin D and Endometrium: A Systematic Review of a Neglected Area of Research.

Growing evidence supports a role of vitamin D (VD) in reproductive health. Vitamin D receptor (VDR) is expressed in the ovary, endometrium, and myometrium. The biological actions of VD in fertility and reproductive tissues have been investigated but mainly using animal models. Conversely, the molecular data addressing the mechanisms underlying VD action in the physiologic endometrium and in endometrial pathologies are still scant. Levels of VDR expression according to the menstrual cycle are yet to be definitively clarified, possibly being lower in the proliferative compared to the secretory phase and in mid-secretory compared to early secretory phase. Endometrial tissue also expresses the enzymes involved in the metabolism of VD. The potential anti-proliferative and anti-inflammatory effects of VD for the treatment of endometriosis have been investigated in recent years. Treatment of ectopic endometrial cells with 1,25(OH)2D3 could significantly reduce cytokine-mediated inflammatory responses. An alteration of VD metabolism in terms of increased 24-hydroxylase mRNA and protein expression has been demonstrated in endometrial cancer, albeit not consistently. The effect of the active form of the vitamin as an anti-proliferative, pro-apoptotic, anti-inflammatory, and differentiation-inducing agent has been demonstrated in various endometrial cancer cell lines.

Human Chorionic Gonadotrophin as a Possible Mediator of Leiomyoma Growth during Pregnancy: Molecular Mechanisms.

Uterine fibroids are the most common gynecologic benign tumors. Studies supporting a strong pregnancy-related growth of leiomyomas generally claimed a crucial role of sex steroid hormones. However, sex steroids are unlikely the unique actors involved as estrogen and progesterone achieve a pick serum concentration in the last trimester while leiomyomas show a typical increase during the first trimester. Given the rapid exponential raise in serum human Chorionic Gonadotrophin (hCG) at the beginning of gestation, we conducted a review to assess the potential role of hCG in the striking growth of leiomyomas during initial pregnancy. Fibroid growth during initial pregnancy seems to correlate to the similar increase of serum hCG levels until 12 weeks of gestation. The presence of functional Luteinizing Hormone/human Chorionic Gonadotropin (LH/hCG) receptors was demonstrated on leiomyomas. In vitro treatment of leiomyoma cells with hCG determines an up to 500% increase in cell number after three days. Expression of cyclin E and cyclin-dependent kinase 1 was significantly increased in leiomyoma cells by hCG treatment. Moreover, upon binding to the receptor, hCG stimulates prolactin secretion in leiomyoma cells, promoting cell proliferation via the mitogen-activated protein kinase cascade. Fibroid enlargement during initial pregnancy may be regulated by serum hCG.