Pigs are considered an ideal source of human disease model due to their physiological similarities to humans. However, the low efficiency of in vitro embryo production (IVP) is still a major barrier in the production of pig offspring with gene manipulation. Despite ongoing advances in the associated technologies, the developmental capacity of IVP pig embryos is still lower than that of their in vivo counterparts, as well as IVP embryos of other species (e.g., cattle and mice). The efficiency of IVP can be influenced by many factors that affect various critical steps in the process. The previous relevant reviews have focused on the in vitro maturation system, in vitro culture conditions, in vitro fertilization medium, issues with polyspermy, the utilized technologies, etc. In this review, we concentrate on factors that have not been fully detailed in prior reviews, such as the oocyte morphology, oocyte recovery methods, denuding procedures, first polar body morphology and embryo quality.

ABSTRACT
 INTRODUCTION
 FOLLICLE DIAMETER
 COC MORPHOLOGY
 OOCYTE RECOVERY METHOD
 IVM OF OOCYTES
 DENUDING PROCEDURES
 MORPHOLOGY OF THE FIRST POLAR BODY
 EMBRYO CULTURE MEDIUM ANDCONDITIONS
 RELATIONSHIP BETWEEN EMBRYOQUALITY AND CULTURE TIME
 IN VITRO FERTILIZATION
 PARTHENOGENETIC ACTIVATION
 SOMATIC CELL NUCLEAR TRANSFER
 IN SUMMARY
 REFERENCES

• Tao Lin(Department of Animal Science & Biotechnology, Research Center for Transgenic Cloned Pigs, Chungnam National University)
• Jae Eun Lee(Department of Animal Science & Biotechnology, Research Center for Transgenic Cloned Pigs, Chungnam National University)
• Hyun Young Shin(Department of Animal Science & Biotechnology, Research Center for Transgenic Cloned Pigs, Chungnam National University)
• Reza K. Oqani(Department of Animal Science & Biotechnology, Research Center for Transgenic Cloned Pigs, Chungnam National University)
• Dong Il Jin(Department of Animal Science & Biotechnology, Research Center for Transgenic Cloned Pigs, Chungnam National University) Corresponding author