The growth of the embryo in the womb
Fertilization and conception of a baby occur when only one sperm enters the egg and gives rise to an embryo. Once out of the follicle, it will take less than 24 hours for the ovum (female reproductive cell) to reach the fallopian tube, the place where fertilization takes place . Sperm (male reproductive cells) have a more difficult time: about 18 cm separate the vagina from the fallopian tube. Therefore, only the most capable sperm will be able to make the journey. Of all of them, only one, the best endowed, will be the one that finally fertilizes the ovum, crossing the wall of the female cell with its head.
Fertilization: the conception of a baby
When sperm and egg meet in the fallopian tube, fertilization occurs. When that single sperm enters the egg, the zona pellucida hardens to prevent the entry of additional sperm. The new cell thus created already contains all the characteristics of the future baby, from the color of the hair and eyes, to the predisposition to suffer from certain diseases.
The embryo and cell multiplication
Once sperm and egg are united, the new cell is called an embryo.
After fertilization, the embryo begins to divide. A cell divides into two cells: two cells make four… and so on, in a geometric progression known as cell division.
At the same time, the embryo begins to migrate down the fallopian tube toward the uterus. The hormonal changes that took place before the release of the egg affect the lining of the uterus (endometrium), which prepares to host the embryo.
The growth of the embryo in the uterus
The embryo detaches from its cortex and implants itself in the uterine membrane. That newly implanted embryo begins to produce a hormone called human chorionic gonadotropin (hCG).
The hCG produced by the embryo is first detected in the woman’s bloodstream. As hCG levels rise, some of it passes through the woman’s kidneys and ends up in the urine.
Blood and urine pregnancy tests are based on the detection of hCG.