Just as formulation of the cell theory was intricately linked to the development of the microscope, IVF and its associated technologies have relied on engineering efforts by many key individuals who have played important roles but unfortunately are rarely remembered. For instance, in 1850, John Lawrence Smith, a faculty member at what is now Tulane University (New Orleans, LA, USA), engineered the inverted microscope. Robert Chambers from New York University (USA) invented the first micromanipulator for cell microsurgery in 1912. The first incubators were used for hatching chicken eggs and date back to ancient Egypt. In the 19th century, this changed to heated bell jars. Carbon dioxide incubators date from the 1960s, and warm-jacketed incubators were developed in the 1970s.

In vitro fertilization-specific instrumentation began to be introduced in the late 1980s, and this process is ongoing with many companies now specializing in the area. The pioneering laboratories relied completely on equipment and materials that were designed for somatic cell tissue culture and not human (or mammalian) gametes and embryos. This is illustrated by the presentations and discussions of the first international group of IVF clinicians and biologists, to convene at Bourn Hall in 1981, to discuss the emerging IVF technology. The 26 attendants came from Basil (Switzerland), Cambridge (United Kingdom), Gothenburg (Germany), Kiel (Germany), Manchester (United Kingdom), Melbourne (Australia), Norfolk, Virginia (USA), Paris (France), and Vienna (Austria). In her chapter on methods of fertilization and embryo culture in vitro in the proceedings of this first conference on clinical IVF, Jean Purdy wrote that, “The equipment needed in a tissue-culture laboratory has been described extensively by Paul (1970)” ( ). This was reflective of a conspicuous lack of specialized equipment and disposables for IVF. Egg collection kits and ET catheters, as well as a pump that allowed gentle aspiration of follicular fluid (FF) from ovarian follicles were among the first IVF-specific instruments/devices to be developed. For the laboratory, laminar flow workstations equipped with heated surfaces were engineered. A benchtop incubator was later invented by David Mortimer and colleagues in Australia as an alternative to “big box” incubators to provide a more stable and controlled culture environment. Incubators have continued to evolve and improve and the present-day embryologists not only culture embryos for longer periods of time, and with more confidence, they can also watch development frame by frame thanks to incorporation of time-lapse microscopy into incubation systems. Close observation of embryos through superior microscopy has contributed to an understanding of the morphology and timing of developmental events and the ability, albeit with limitations, to select/deselect embryos for transfer and cryopreservation.

Tissue culture media were first developed nearly 150 years ago by Ludwig and Ringer. These were simple salt solutions, which were based on the properties of serum/blood plasma. Knowledge was gained during those years about the biochemistry of metabolism in mammals and humans, particularly osmolarity, pH, and temperature. This knowledge provided the basis for modifications to the simple salt solutions and successive generations of culture media, which were considerably more complex. The second generation of culture media was developed in the 1970s, mimicking the female reproductive tract environment. This was followed by a third generation of media, which was designed to optimize growth in vitro, to some extent ignoring existing formulations and the “back to nature” principle behind those formulations. To formulate these new media, the performance of each ingredient was evaluated separately using a “simplex optimization” process. This was first developed for mouse embryo culture by Professor John Biggers at Harvard University. His work was supported by the US National Institutes of Health, in part aiming to develop culture media for use in the human while circumventing the moratorium still in place on human embryo research. Variations on the second-generation media, called sequential and third generation simplex optimized-derived media are still in use at present and seem equally effective in supporting development of human embryos through 6 or 7 days of culture in vitro. The departure from home-brew culture media and the acceptance of commercially manufactured media, which is strictly regulated by governmental agencies, very likely has contributed to improvements in laboratory and clinical outcomes by virtually eliminating inconsistencies, manufacturing errors, and batch-to-batch variability.

Culture systems have evolved too. In the 1930s, Carrell flasks (Gregory Pincus) were used to culture embryos or perform in vitro insemination. In the 1950s, experimental embryologists like John Hammond and Wesley Whitten switched to test tubes. In 1963, Ralph Brinster introduced the culture of eggs and embryos in small droplets of culture medium under a layer of paraffin oil ( ). With some modifications, this ingenious “micro-drop” method using the Petri dish has become the most widely used and successful system for culture of mammalian embryos in vitro. Brinster’s contributions were for a long time unappreciated by human IVF specialists; early on, nearly all practitioners used either organ culture dishes or small test tubes for culture of human gametes and embryos. But eventually, by the mid-1990s, most IVF laboratories adopted the “closed” under-oil culture system. There is little doubt that this system has provided a better, more stable environment and significant advantages for embryonic growth, which were lacking in the open culture systems of the past. This in turn has led to increased efficiency and efficacy of embryo culture.

Clinical embryology did not evolve in a vacuum but against a backdrop of a 150-year history in experimental embryology, cryobiology, and other related fields. When Bourn Hall Clinic opened in 1980, Jean Purdy hired two laboratory assistants who worked as quality control technicians. They handled the Petri dishes, completed the paperwork, and witnessed procedures. The clinical embryologists, on the other hand, were charged with the handling of gametes (including sperm preparation) and embryos and communication with patients. The pioneering embryologists were often involved in optimizing follicular recruitment protocols and timing of egg retrievals. By 1983, when Louise Brown turned 5 years, worldwide fewer than 100 embryologists were involved in clinical work. They experienced a very different work environment than exists at present—so much was unknown and there was little guidance. At present, aspiring embryologists can participate in Master of Embryology programs, and they can get training in specific technologies and techniques through courses, which provide hands-on experience. Embryologists and trainees can reinforce and expand their theoretical knowledge through a rich literature of thousands of articles, dozens of textbooks and “how-to” books, and attend one of the many specialized workshops organized annually around the world. They can watch videos on the Internet or participate in web-based journal clubs and discussion groups. In some countries, embryology directors and managers must attain postgraduate credits to keep qualification standards and their laboratories must be audited and certified. These new opportunities have provided for an expansion of the workforce and the possibility to more appropriately staff ART laboratories. Proper staffing itself is a significant contributor to improved safety and better outcomes ( ).

During the years, the IVF laboratory has incorporated many transformative technologies that have continued to be refined and perfected. Most important have been oocyte and embryo cryopreservation; assisted fertilization for treatment of male factor infertility; genetic diagnosis of embryos before transfer; and development of new embryo selection methodologies and platforms, including embryo morphokinetics using time-lapse microscopy.

Consideration of a cell’s physiology is a logical starting point when trying to culture it. This premise is challenging when considering the preimplantation human embryo, whose physiology and metabolism changes dramatically from fertilization to implantation. The fertilized oocyte and cleavage-stage embryo are relatively quiescent, exhibit limited oxidative capacity, and use carboxylic acids predominantly. In contrast, the blastocyst is one of the most active tissues in the body, characterized by exponential growth, expansion of a blastocoel, increased oxygen use and oxidative metabolism, a large demand for glucose (largely to support biosynthetic requirements), and a somewhat paradoxical production of lactate through aerobic glycolysis (thought to be key in embryonic signaling with the endometrium) (Fig. 1). The dynamics and complexities of preimplantation embryo physiology, therefore, help to explain the long and complex road to blastocyst transfer.