It’s almost impossible to know the exact moment of conception and so it’s very tough to know about the first week of pregnancy. Therefore, doctors and other health care professionals count your due date as 40 weeks from the starting day of your last menstrual period (LMP). This means that they count your period as part of your pregnancy, even though you have not conceived yet.
During menstruation, the female human body produces the follicle-stimulating hormone. This hormone helps the development of an egg in your ovary. The egg matures within a follicle. The follicle is a small cavity in your ovary. After menstruation ends, your body produces the luteinizing hormone. This hormone causes the release of the egg; the process is called ovulation. The human body has two ovaries, however, ovulation occurs from just ovary. The egg moves slowly into the fallopian tube (which connects your ovary and uterus) and waits for a fertilizing sperm. If a woman has had intercourse before or during this time, she can become pregnant. If fertilization doesn’t occur, the egg and the lining of her uterus will be shed through her menstrual period.
The process of conception begins when you and your partner have sexual intercourse. When he ejaculates, your partner semen containing up to 1 billion sperm cells into your vagina. Each sperm has a long, whip-like tail that propels it toward your egg. Many millions of these sperm swim through your reproductive tract into the lower opening of the uterus (called the cervix), and through the uterus and into the fallopian tube. Only a fraction of the sperm released reach the fallopian tube. Fertilization takes place when a single sperm penetrates the wall of the egg.
Pregnancy Tests – If a woman takes a pregnancy test on the first day she misses her period, there’s 10 percent chance of a false negative reading (according to The Journal of the American Medical Association). Therefore, assume you are pregnant and retest a week later.
Once a sperm has made its way into the egg, the single-cell fertilized egg (called zygote is your baby during fertilization) immediately forms a barrier around itself to keep out other sperm. The zygote has 46 chromosomes — 23 from you and 23 from your partner. These chromosomes determine your baby’s sex (boy or girl) and traits such as eye and hair color. Therefore, these traits have been set at the very moment of conception. A woman’s egg contains only X-chromosomes, whereas, the sperm contains both X and Y chromosomes. If a sperm with an X chromosome combines with the egg (X chromosome), we will have a girl. On the other hand, if a sperm with a Y chromosome combines with the egg (X chromosome), we will have a boy. The father’s genetic contribution determines the baby’s sex. Within hours, the zygote divides into two cells, then four, and so on, until the cluster consists around 100 cells just a few days later. Some of these cells will form the embryo, and others the placenta.
After fertilization, the cluster of cells will go through the fallopian tube and implant itself into the wall of your uterus. Twins can occur in two ways – fraternal twins occur when two separate eggs are fertilized by two different sperm. This means that each baby has his own placenta and amniotic sac. However, if one fertilized egg develops into two fetuses, we will have identical twins. They might share a placenta, but each baby usually has a separate amniotic sac.