Ovulation usually occurs around the 14th day of a 28-day cycle, or a little later if your cycle is longer. Ovulation is basically your body’s process of releasing a mature egg cell from one of your ovaries. It travels down the fallopian tube where it patiently waits for a sperm cell.

Over the next 12 to 24 hours, if the sperm penetrates into your egg, fertilization occurs. It takes about 20 minutes for the lucky sperm to unite with the egg. When this happens, the sperm's nucleus will merge with the egg's nucleus, forming a zygote, which will grow as a baby over the next nine months.

By this time though, your developing baby is just a little ball of cells but it is growing amazingly fast. It has a fluid-filled cavity that will become the amniotic sac, an outer cell mass that will become the placenta, and an inner cell mass that will become the embryo.