Time-lapse incubators have become increasingly popular in assisted reproductive technology, allowing for the observation of the developmental process, which may be useful in the selection of human embryos suitable for transplantation. Dynamic morphological changes of chromosomes and the cytoskeleton occur during early embryonic development, including in humans, and abnormalities such as embryonic chromosomal aneuploidy occur when development does not proceed normally. Chromosome and cytoskeletal dynamics are difficult to observe with time-lapse bright field monitoring. However, in recent years, live-cell imaging techniques have been used to analyse these dynamics by injecting fluorescently labelled cytoskeletal proteins or mRNA encoding fluorescein probes. These require complicated procedures and necessitate mechanical invasion of cells. Here, we introduced a fluorescence-labelled probe with cell-membrane permeability that specifically adheres to DNA and to the cytoskeleton as imaged in an incubator-integrated time-lapse confocal laser microscope observation system. This platform enabled us to analyse, in detail, the dynamics of chromosomes, microtubules, and microfilaments from the fertilized pronuclear zygote, through first cleavage, to 2-cell stage embryo. This method is simple and does not require genetic manipulation, and its application can be expected to provide novel insights into embryonic development in many mammals, including humans.

Retained products of conception (RPOC) are frequently associated with previous cesarean section (Csection), abortion, and intrauterine operations, which may affect subsequent pregnancies. A 38-year-old female had a history of C-section and two abortions. After the second abortion, she underwent evacuation of RPOC and was treated with uterine artery embolization (UAE) and hysteroscopic resection. She became pregnant again and vaginally delivered an infant at full term. After delivery, RPOC was suspected on magnetic resonance imaging (MRI), but the patient was discharged for follow-up. She was rehospitalized with a diagnosis of infection and a placental remnant. Antibiotics did not improve the infection; therefore, she underwent a total hysterectomy. After the operation, signs of infection rapidly improved. The pathological diagnosis was placenta accreta. This case was considered a high-risk group for RPOC. In such rare and complicated cases, it is important to consider the possibility of recurrent RPOC and provide sufficient explanations before delivery for subsequent intensive management.

Dynamic morphological changes in the chromosomes and cytoskeleton occur in mammals including humans, during early embryonic development, and abnormalities such as embryonic chromosomal aneuploidy occur when development does not proceed normally. In previous reports, the behavior of DNA and cytoskeleton in early mammalian embryos has conventionally been visualized and observed by injecting target molecule mRNA, with a fluorescent substance-expressing gene incorporated, into embryos. However, injecting genetic information into a human embryo to induce the production of unnatural proteins must be carefully considered from an ethical perspective. Therefore, we aimed to develop a simple observation method as a way of gaining knowledge about the first division that can avoid such problems. We visualized the chronological behavior of male and female chromosome condensation in mammalian embryos, beginning in the 2PN zygote, through the first division into the two-cell stage by using fluorescent chemical probes for DNA, microtubules, and microfilaments. This method is simple and does not require genetic manipulation, and its application can be observed at any stage during embryonic development, thereby providing novel insights into embryonic development in many mammals. In particular, it is expected to provide a great deal of cell biological information on the first cleavage of human embryos, which have been reported to exhibit a variety of patterns.