Early development
Day four after conception
- morula-stage embryo arrives in uterus.
- Morula develops into blastocyst over next two days
- implants in dorsal wall of uterus by digesting some cells of endometrium
- embryo that implants in fallopian tubes or cervix does not survive
- ecotopic pregnancy puts mother’s life at risk
Inner mass of cells, on one side of blastocyst cavity, turns into the baby itself
- peripheral mass of cells, the trophoblast, forms extra-embryonic membranes and in time establish fetal portion of placenta.
- Trophoblast cells etch their way into the uterine wall, establishing indirect connections with maternal blood supply.