Early embryonic development is crucial for individual health. Abnormal early embryonic development may lead to early pregnancy loss, birth defects, and developmental-originated diseases. The in-depth study of embryonic developmental events is essential for understanding biological and pathological pregnancy. However, mammalian embryonic development takes place in the uterus, which hinders direct obversion and manipulation. The in vitro culture (IVC) of mammalian embryos is a class of systems that provides suitable conditions to support the ex utero development of mammalian embryos, especially for post-implantation embryos.

In the past 70 years, various IVC systems have evolved to support the development of mammalian embryos. Currently, mouse E5.5 embryos have been in vitro cultured up to the E11-like stage by a roller culture system 1, 2••. Human blastocysts have been successfully cultured to the E14 using 2D and 3D culture systems 3, 4, 5, 6. Per ethical guidelines, the culture of human embryos must be terminated before E14 or before the appearance of the primitive streak [7], precluding the studies of post-E14 embryonic developmental events such as gastrulation using IVC embryos 5, 6, 8••, 9, 10, 11. Macaques have been considered a reliable animal model for studying human physiology and pathology because of their evolutionary, genomic, and physiological similarities to humans. Their embryos shared close morphological characteristics and development clock with human embryos from zygote to E30, indicating their reliability for application to the studies on early human embryogenesis [12]. Recently, macaque blastocysts have been successfully cultured up to E25 13••, 14••, 15••, 16••. These advancements in culture systems have facilitated the investigation of gastrulation and early organogenesis in primate embryos (Figure 1).

Mammalian embryo IVC systems can be used not only to explore developmental biology mechanisms but also to reveal pathological development and advance regenerative medicine. For example, some systems were chosen for establishing teratogenesis and drug screening models [17]. Additionally, some IVC systems have been applied to the culture of stem cell–based embryo models (embryoids), assisting mouse embryoids in vitro developing to the E8.5-like stage, and macaque embryoids to the E16-like stage 18, 19, 20, which might provide novel avenues for obtaining development-based progenitor cells or organ anlages [21]. Despite these advancements, IVC systems still face several practical challenges, resulting in some inconsistencies between IVC embryos and their in vivo counterparts. In this review, we systematically summarize the development of IVC systems for early mammalian embryos, covering mouse, human, and macaque; highlight key advancements in these culture systems; and provide our insights into optimizing the IVC system.