Conception occurs when one of the millions of sperm from the male's semen fertilizes an ovum. Almost immediately the fertilized ovum begins to divide repeatedly into numerous cells, the building blocks of the new human. If all goes well, the ball of cells attaches itself within the uterus (or womb) and continues to grow while a cavity (called the extraembryonic coelom) forms inside. At one point on the cavity lining begins a growth called the inner cell mass. This mass develops two cavities - the amniotic cavity (bag of waters) and the yolk sac. The disc of tissue separating the two cavities is the germ disc, the earliest stage of the embryo. As the yolk sac shrinks away, the embryo curls around it and matures into a fetus. The stalk becomes the umbilical cord and its site of attachment to the womb becomes the placenta (which allows the embryo to get nutrition from the mother's bloodstream). This sequence of events takes place during the first few weeks of pregnancy.
Note: The material provided in this web page is educational in nature and not medical advice. It is meant neither for self-diagnosis nor as a treatment recommendation. If you are concerned about any condition you think you may have, CONSULT YOUR DOCTOR.