Endometrial preparation is crucial in in vitro fertilization (IVF) protocols to create optimal conditions for embryo implantation and pregnancy. Successful embryo nidation requires a receptive endometrium, which is influenced by factors such as endometrial thickness, hormonal environment, autocrine and paracrine growth factors, and the presence of resident and non-resident stem cells within the endometrium basalis. Synchronization between endometrial and embryonic development is also essential. Endometrial preparation, whether achieved through spontaneous cycles, natural cycles with minimal support, ovulation induction, or hormone replacement therapy (HRT), results from a combination of biochemical and biophysical conditions, each independent of the others. These conditions are difficult to pinpoint within a fixed period (Window of Implantation, WOI) using any specific examination due to the variability in estrogen and progesterone production rates, their metabolic clearance rates (MCR) when administered exogenously, and their metabolism when given systemically, topically, or orally. These variations also occur in different phenotypes and over different durations. Moreover, the synchronization of endometrial preparation with incomplete decidualization and the uncertain duration of the implantation window pose challenges. It is also unknown if there are compliance mechanisms similar to diapause seen in other species. This review aims to outline a clinical approach that, while not an absolute clinical recommendation due to the lack of definitive certainties, assists in understanding complementary phenomena and provides a useful orientation for clinical practice.

Over the past two decades, fertility services have experienced significant shifts in ownership structures worldwide, transitioning from predominantly public or physician-owned clinics to a market increasingly influenced by private equity. These changes raise debates about treatment efficacy, cost transparency, and the ethical implications of profit-driven health care. This review provides an evidence-based overview of trends in fertility clinic ownership (public, physician-owned, and private equity-backed), along with reported success rates and implications for treatment quality, cost transparency, and patient well-being. A narrative synthesis was conducted using peer-reviewed literature, registry data, and industry reports published between 2000 and 2025 (projected). Ownership distribution, reported live birth rates, and financial transparency were examined. Regional studies, market analyses, and professional guidelines were used to infer trends when global data were unavailable. Ownership trends show a decline in public- and physician-owned clinics, with private equity projected to control up to 50% of fertility centers in some regions by 2025. Treatment efficacy improved across all clinic types, with live birth rate per in vitro fertilization cycle rising from ~25 – 30% in 2000 to ~35 – 45% by 2020 in younger cohorts; higher rates in private equity clinics may reflect patient selection and reporting variability. Cost transparency remains inconsistent, particularly in private equity networks where bundled pricing and aggressive marketing may obscure true costs and incentivize unnecessary add-ons. The consolidation of fertility centers under corporate ownership has reshaped reproductive health care. Ongoing concerns include pricing opacity, the clinical value of “add-on” treatments, and the ethical positioning of clinicians in profit-driven settings.