How does fertilization work

The uterus also has little finger like structures called cilia that help move the sperm, hopefully, towards the egg 1. Sperm triggers an immune response when it enters the uterus 5. Also, sperm may end up going up the wrong fallopian tube.

The vast majority of the time, a person only releases one egg from one ovary. That means that only one of the two fallopian tubes will have eggs, and some sperm will have gotten it wrong. Only a tiny fraction of the sperm that entered the vagina make it to the fallopian tube 5. As the fallopian tube pushes the egg towards the uterus, cilia push the sperm towards the egg.

Progesterone and estrogen influence this process by increasing the number of cilia and how fast they move 1. The egg and surrounding cells produce a chemical that attracts sperm 1,7. Sperm may be attracted to the temperature at the ovarian-end of the fallopian tube, which tends to be warmer 1,5. As they travel through the fallopian tubes, sperm gain the ability to fertilize an egg 1.

Break through a group of cells known as the cumulus oophorus that surround the egg. The sperm dissolves these cells using an enzyme 1,7. Break through the outer membrane of the egg. The sperm essentially fuses to and digests this membrane using an enzyme 1,7. Once a sperm has penetrated an egg, this membrane changes, and becomes impenetrable to other sperm 1,7. Once it meets the egg, the nuclei from the egg and sperm merge and share their genetic material 1,7.

If all this goes well, what fertilized egg becomes a zygote 1,7. The egg now contains all the genetic material it will need to become a person. It takes about days for the fertilized egg to travel to the uterus and attach to the uterus in a process known as implantation 1,8. The egg is pushed back towards the uterus by the cilia 1. The egg must attach to the uterus to become a viable pregnancy. While traveling to the uterus, the egg has been dividing and forming a few different structures 7.

Once that barrier is broken down, the blastocyst can attach to the endometrium 1. Sometimes, though, a fertilized eggs can't make it to implantation. These losses generally aren't considered miscarriages, as most healthcare professionals consider a pregnancy to have begun at implantation. However, people who think or know they lost a fertilized egg such as people using artificial reproductive technologies may consider this to be akin to a more traditional miscarriage.

The egg takes several days to travel down the fallopian tube into the uterus. After it is in the uterus, a fertilized egg usually attaches to implants in the lining of the uterus endometrium.

But not all fertilized eggs successfully implant. If the egg is not fertilized or does not implant, the woman's body sheds the egg and the endometrium. This shedding causes the bleeding in a woman's menstrual period. When a fertilized egg does implant, a hormone called human chorionic gonadotropin hCG begins to be produced in the uterus.

This is the hormone that a pregnancy test measures. It prevents the uterine lining from being shed, so the woman does not have a period. Other signs such as breast changes and nausea occur in a woman's body, also meaning that pregnancy has begun.

Author: Healthwise Staff. This information does not replace the advice of a doctor. Healthwise, Incorporated, disclaims any warranty or liability for your use of this information. Most women are able to become pregnant from puberty , when their menstrual cycles begin, until menopause , when their cycles stop.

A pregnancy starts with fertilization, when a woman's egg joins with a man's sperm. Fertilization usually takes place in a fallopian tube that links an ovary to the uterus. If the fertilized egg successfully travels down the fallopian tube and implants in the uterus, an embryo starts growing.

All the eggs for a woman's lifetime are stored in her ovaries. Women do not keep producing eggs. This is different from men, who continuously make more sperm. About once a month, an egg is released from one of a woman's two ovaries. This is called ovulation. The egg then enters the nearby fallopian tube that leads to the uterus. If a woman and a man have unprotected sexual intercourse, sperm that is ejaculated from the man's penis may reach the egg in the fallopian tube.

If one of the sperm cells penetrates the egg, the egg is fertilized and begins developing.