During ovulation, one of the ovaries releases an egg, which then travels down one of the fallopian tubes. Usually, an egg has about 12 to 24 hours where it can be fertilized by sperm.
Therefore, when the ovary releases the egg, sperm that are already present from intercourse a few days before could fertilize it. Or, if a woman has sex during the time the egg has been released, the sperm could fertilize the just-released egg. Most doctors usually recommend having unprotected sex starting about three to six days before you ovulate, as well as the day you ovulate if you wish to become pregnant. Conception requires several steps to come together.
First, a woman must release a healthy egg. Some women have medical conditions that prevent them from ovulating altogether. A woman must also release an egg healthy enough for fertilization. A woman is born with the number of eggs she will have throughout her lifetime. As she gets older, the quality of her eggs diminishes. This is most true after age 35, according to the Royal College of Obstetricians and Gynaecologists. High-quality sperm are also required to reach and fertilize the egg.
While only one sperm is needed, the sperm must travel past the cervix and uterus into the fallopian tubes to fertilize the egg. Some conditions cause the sperm to die before they can swim to the fallopian tubes. Some women may benefit from assisted reproductive technologies like intrauterine insemination or in vitro fertilization if there are issues preventing healthy sperm from meeting a healthy egg naturally.
Sperm usually fertilizes the egg in the fallopian tube. An egg takes about 30 hours to travel from the ovary down the fallopian tube, according to the University of California San Francisco.
As the egg travels down the fallopian tube, it lodges in a specific portion called the ampullar-isthmic junction. The first sperm enter the tubes minutes after ejaculation. The first sperm, however, are likely not the fertilizing sperm. Motile sperm can survive in the female reproductive tract for up to five days. Egg transport begins at ovulation and ends once the egg reaches the uterus.
Following ovulation, the fimbriated, or finger-like, end of the fallopian tube sweeps over the ovary. Adhesive sites on the cilia, which are located on the surface of the fimbriae, are responsible for egg pickup and movement into the tube.
The cilia within the tube, and muscular contractions resulting from the movement of the egg, create a forward motion. Transport through the tube takes about 30 hours. Conditions such as pelvic infections and endometriosis can permanently impair the function of the fallopian tubes, due to scarring or damage to the fimbriae. Following ovulation, the egg is capable of fertilization for only 12 to 24 hours. Contact between the egg and sperm is random. Once the egg arrives at a specific portion of the tube, called the ampullar-isthmic junction, it rests for another 30 hours.
Fertilization — sperm union with the egg — occurs in this portion of the tube. The fertilized egg then begins a rapid descent to the uterus. The period of rest in the tube appears to be necessary for full development of the fertilized egg and for the uterus to prepare to receive the egg. Defects in the fallopian tube may impair transport and increase the risk of a tubal pregnancy, also called ectopic pregnancy.
A membrane surrounding the egg, called the zona pellucida, has two major functions in fertilization. First, the zona pellucida contains sperm receptors that are specific for human sperm. Second, once penetrated by the sperm, the membrane becomes impermeable to penetration by other sperm. Following penetration, a series of events set the stage for the first cell division. Bookmark BookmarkTick BookmarkAdd save. This is going to sound like a dumb question, but how does conception actually occur?
I don't understand why doctors start counting the number of weeks pregnant from the last period. Doesn't ovulation happen after that? By Paula Kashtan. Next on Your Reading List. If you have shorter cycles, say 21 days, ovulation happens around day 7 and your most fertile days are days 5, 6 and 7. FACT A woman can only get pregnant on a few days during her menstrual cycle. Because eggs and sperm only live for a short time: Sperm live for around five days.
Eggs can only be fertilised for around 24 hours one day after being released from the ovary. Getting the timing right If you're trying to get pregnant, timing is everything. What are the chances?
Having sex as close as possible to the time of ovulation increases the chance of pregnancy. If she has sex five days before she ovulates, her probability of pregnancy is about 10 percent. When does preconception health begin? How to know you are ovulating Kerry Hampton, a registered nurse and fertility specialist, discusses the importance of fertility awareness, and how to determine your fertile window to improve your chances of conceiving.
Identification and prediction of the fertile window using Natural Cycles. Self-identification of the clinical fertile window and the ovulation period. Fertility and Sterility, 5 , Optimizing natural fertility: a committee opinion.
Fertility and Sterility, 1 , Revisiting the fertile window. Timing intercourse to achieve pregnancy: current evidence. Obstetrics and Gynecology, 6 , Stephenson, J.
Before the beginning: nutrition and lifestyle in the preconception period and its importance for future health. The Lancet, Pet al.
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