During human in vitro culture, a morphological microscope analysis is normally performed to select the best embryo to transfer, with the hope of obtaining a successful pregnancy. The morphological evaluation may combine number and size of blastomeres, fragmentation, multinucleation, blastocyst expansion, inner-cell mass and trophectoderm appearance. However, standard microscopy evaluation involves the removal of the embryos from the incubator, exposing them to changes in pH, temperature, and oxygen level. Additionally, morphological assessments might include high inter-observer variability. Recently, continuous embryo culture using time-lapse monitoring (TLM) has allowed embryologists to analyse the dynamic and morphokinetic events of embryo development and, based on that, the embryologist is able to scrutinize the complete sequence of embryonic evolution, from fertilization to the blastocyst formation. Therefore, TLM allows an uninterrupted culture condition, reducing the need to remove embryos from the incubator. The monitoring system is normally composed of a standard incubator with an integrated microscope coupled to a digital camera, which is able to collect images at regular times, and subsequently processed into video. These data can be annotated and analyzed using an integrated software, therefore this allows embryologists to facilitate the process of embryo selection for transfer. The main aim of this paper is to discuss the potential benefits and uses of the TLM in the embryology laboratory.

When egg storage periods are prolonged (>7 days), hatchability and chick quality declines. The reason for this decline has been investigated, but is still not completely understood. At oviposition the developmental stage of the chicken embryo varies and so do the total number of viable cells. During storage, changes can occur in the embryo. Embryo viability at the end of storage seems to be dependent on the number of viable cells and the developmental stage of the embryo at oviposition. When the hypoblast is completely formed (during the quiescent developmental stage), the embryo seems to be more able to endure prolonged storage periods than embryos that are less or more advanced. During storage, changes also occur in egg characteristics such as albumen viscosity, albumen pH and yolk pH. There appears to be an interaction between albumen pH and embryo viability during early incubation and perhaps also during storage. An albumen pH of 8.2 seems to be optimal for embryo development. Albumen pH may influence embryo viability, but embryo viability may in turn, affect albumen pH. It has been hypothesised that an embryo in which the hypoblast is completely formed is better able to provide an effective barrier between the internal embryo and the exterior (yolk and albumen) and/or is better able to produce sufficient amount of carbon dioxide, which will reduce the pH level in the micro environment of the embryo to the optimal pH of 8.2. It appears that, to maintain hatchability and chick quality after prolonged storage periods, embryonic development should be advanced to the stage in which the hypoblast is completely formed or the atmosphere during storage and early incubation should be altered in such a way that albumen pH is maintained at the optimal level of 8.2.

The number of cells in a preimplantation embryo is directly correlated to the health and viability of the embryo. There are currently no methods to count the number of cells in late-stage preimplantation embryos noninvasively. We assessed the ability of optical quadrature microscopy (OQM) to count the number of cells in mouse preimplantation embryos noninvasively. First, to test for possible light toxicity, we exposed two-cell mouse embryos to OQM and differential interference contrast (DIC) microscopy and assessed their ability to develop to the blastocyst stage. We found no inhibition of development from either mode of microscopy for up to 2 h of light exposure. We also imaged eight-cell to morula stage mouse preimplantation embryos by OQM nd developed two methods for counting the number of cells. The contour signature method (CSM) used OQM images alone and the phase subtraction method (PSM) used both OQM and DIC images. We compared both methods to standard cell counting techniques and found that the PSM was superior to all other noninvasive cell counting methods. Our work on mouse embryos should be applicable to human embryos. The ability to correctly count the number of cells in human preimplantation embryos could lead to the transfer of fewer embryos in in vitro fertilization (IVF) clinics and consequently a lower rate of high-risk multiple-infant births.