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. Sometimes, the egg attaches somewhere else, like to the fallopian tube, and the pregnancy will not be viable.
This is called an ectopic pregnancy and should be treated as a medical emergency. Although it can go wrong, it's pretty amazing how often our bodies do get it right. Article originally published 29 June Science is evolving each day on how coronavirus affects pregnancy, lactation, and postpartum. At week 4 , the blastocyst implants into the wall of the uterus. The blastocyst contains an inner and an outer part.
The inner part will ultimately develop into the embryo. The outer part will become the placenta, an outer shell that will provide protection and nourishment to the growing embryo. At this point, the baby is a cluster of cells measuring approximately 0. Around the beginning of week 5 , doctors will likely start referring to the baby as an embryo, and it will be about the size of a sesame seed. You may need to take a break from strenuous exercise during pregnancy, and a doctor can help modify or develop a healthful exercise plan.
During the first 6 weeks of pregnancy, there may be no indications of pregnancy. However, soon after fertilization in some cases, and increasingly as time goes on, you may experience:. A pregnancy test is likely to produce an accurate result if a person takes it 1 week after the first day of the next expected period. Learn more. Fetal macrosomia is a condition wherein a baby is born at a heavier birth weight than usual.
Learn more about fetal macrosomia here. A study links air pollution to almost 6 million premature births each year. Indoor air pollution is responsible for two-thirds of these perinatal…. Amniotic fluid embolism is a dangerous pregnancy complication that develops due to a severe allergic reaction. Learn more about it, including symptoms,.
Pregnancy dreams can be more realistic, detailed, or frightening than usual. However, they are not usually a cause for concern. Learn more here. Your pregnancy at week 3. Medically reviewed by Debra Sullivan, Ph. Fertilization How does it happen? What are chromosomes? Products and services. Free E-newsletter Subscribe to Housecall Our general interest e-newsletter keeps you up to date on a wide variety of health topics. Sign up now. Fertilization and implantation During fertilization, the sperm and egg unite in one of the fallopian tubes to form a zygote.
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