Blastocyst
While the zygote is in the uterine tube (@ about day 4 ) it divides into a ball of 12 - 16 cells. Around the 10th day the inner portion of the zygote (blastocyst) implants into the uterine lining. The outer portion of the zygote becomes the placenta.
After puberty, the vaginal lining becomes stratified squamous epithelium to allow fast diffusion of nutrients in case a zygote is implanted.
The answer to your question is a zygote. From there, it develops to an embryo and a foetus. Happy science!!!
The uterine lining builds-up in preparation for fertilization so that the zygote/embryo can implant itself into the uterine lining and then develop into a baby. Menstruation only takes place when fertilization doesn't take place, this occurs so the uterine lining is shed and can start a fresh next cycle so it can be ready for pregnancy again. If the uterine lining were to break down after fertilization a zygote/embryo wouldn't be able to implant itself or it would result in miscarriage.
A zygote becomes a fertilized egg when it is implanted. That grows into a fetus for the 9 months and is a baby after it is born.
In plant plot xD
Implantation.
The uterine lining builds-up following ovulation in preparation for possible pregnancy, to allow the zygote to implant and nourish the growing 'baby'. If pregnancy doesn't occur the drop in progesterone triggers the uterus lining to break down, this is called menstruation.
A zygote becomes a fertilized egg when it is implanted. That grows into a fetus for the 9 months and is a baby after it is born.
implantation
Implantation
A zygote is single cell which is formed immediately after fertilization . IT then converts to morula followed by blastula (ZYGOTE DIVIDED INTO 16-32 cells) WHICH GETS IMPLANTED IN THE UTERINE WALL . IT THEN DIVIDES TO FORM EMBRYO WHICH AFTER 9 MONTHS IS RECOVERED FROM THE MOTHER
Implantation is the medical term meaning attachment of the zygote to the uterine wall. If the zygote does not attach, a period occurs.