|
|||||||||||||||
Week 1 |
|
|
|
|
|
|
|
|
|
|
Blastocyst completed/ implanted |
Primitive placental circulation established |
|
|
|
| * |
Initiation of Stage 1 Fertilization |
Initiation of Stage 2 Zygote divides |
Morula |
Initiation of stage3 Early blastocyst |
Late blastocyst |
Initiation of Stage 4 Implantation stage |
Initiation of stage 5 |
* |
Bilaminar disc |
Appearnce of lacunae |
Epithelium growing over the surface of the defect |
Coelom |
Primary villi Initiation of stage 6 |
Dorsal side of the embryo |
|
| * |  Stage 1 of embryo development: Embryo starts to develop after fertilization of the oocyte about 14 days after the LMP. |
Stage 2 of embryo development: The ovum starts to cleave during stage 2. Continuous division results in the formation of morula. Morula enters the uterine cavity on day 3. |
Stage 3 of embryo development: During this stage, blastocyst is formed. |
Stage 4-5 of embryo development: During stages 4 and 5, blastocyst attaches to the endometrium and starts to penetrate it. |
* | Stage 6 of embryo development: This stage starts at the end of the second week. During this time, the bilaminar embryonic disc and primary chorionic villi are formed. |
True beginning of gestation starts with the fertilization of the ovum which normally occurs one to several days after ovulation. By convention, however, due the fact that the day of the last menstrual period is easily defined, gestation starts on such day. During the first two weeks of pregnancy the embryo does not exist and endometrium is undergoing its normal menstrual and then proliferative phases. Stage one of the development starts with the fertilization of the ovum and stage 2 is initiated by the cleavage of the fertilized ovum. It is during the 4th and 5th stages of development that blastocyst starts its implantation process. By the end of the second week after fertilization, the stage 6 is initiated. During this stage, the primary chorionic villi and embryonic disc are formed. |
||||||||
|