Embryo Development and Implantation

**63**

**Chapter 5**

**Abstract**

**1. Introduction**

Development

*Hilma Putri Lubis and Binarwan Halim*

endometrial signals in the apposition stage.

**2. Physiology of the blastocyst**

Human Blastocyst Formation and

The preimplantation period of human embryo development is remarkable and characterized by successive changes in terms of genetic control, physiology, and morphology of the embryo. Human preimplantation embryo development is characterized by the initial phase of embryo development, the phase before the embryo implantation process. In normal conditions, after fertilization, the embryo grows until the blastocyst stage. The blastocyst grows as the cells divide and the cavity expands, where it "hatches" from the zona pellucida to implant into the endometrium. Reprogramming and programming are continuous processes in the embryo that encompasses fusion of the egg and sperm pronuclei; epigenetic reprogramming and modification, an extensive wave of degradation of maternal transcripts, and activation of the nascent human embryonic genome and aneuploidy can occur in this stage. The embryo produces cytokines, growth factors, and receptors for

**Keywords:** preimplantation, embryo, epigenetic, reprogramming, blastocyst

Preimplantation embryo development is characterized by a series of events after fertilization including the formation of the maternal and paternal pronuclei, followed by the formation of the zygote, which at ±20 hours after insemination starts undergoing mitotic divisions every 12–18 hours (cleavage stage), reaching the morula (compaction), and the blastocyst grows as the cells divide and the cavity expands, until it arrives at the uterus, where it "hatches" from the zona pellucida to implant into the endometrium. The main objective of blastocyst culture was to increase the success rate of in vitro fertilization (IVF) because of better embryo selection. Blastocyst culture has also been used as a tool to select the most viable embryos in a cohort with a consequent reduction in the number of embryos transferred and the corresponding reduction in the incidence of multiple gestations. This chapter will review about human blastocyst formation and development and discuss about the physiology, morphology, and gene expression of the blastocyst.

The transformation of the fertilized oocyte into the blastocyst is not only characterized by major morphological events but also by dramatic changes in its
