As a woman, you know how to get pregnant (i.e. sex), but you may not know where exactly fertilization occurs. Pregnancy can be a complex, complicated topic, and it’s perfectly normal to be confused or unsure of how certain processes actually happen.
Here are 10 things you need to know about fertilization, including where it occurs.
Table of Contents
- 10 Things You Should Know About Fertilization
- ① Fertilization Occurs in the Fallopian Tube
- ② Fertilization Can Only Occur During Ovulation
- ③ Ovulation Isn’t Always Obvious
- ④ Fertilization is a Miraculous Thing
- ⑤ Once Fertilized, the Egg Changes
- ⑥ Implantation Occurs in the Uterus
- ⑦ Implantation May Cause Light Bleeding
- ⑧ Implantation Usually Occurs 6-10 Days after Ovulation
- ⑨ Implantation Isn’t Always Successful
- ⑩ Miscarriages Are Common Even After Implantation
10 Things You Should Know About Fertilization
① Fertilization Occurs in the Fallopian Tube
It’s easy to assume that fertilization occurs in the uterus (most women do), but sperm actually fertilizes the egg in the fallopian tube.
In some cases, fertilization occurs on the outside of the reproductive tract, which can be dangerous. This is known as an ectopic pregnancy, and it can be a life threatening condition.
② Fertilization Can Only Occur During Ovulation
Ovulation is the only time sperm can fertilize an egg. To understand how this works, you need to understand your menstrual cycle.
Every month, a group of eggs start to grow inside of your uterus in tiny sacs called follicles. These eggs continue to grow until one erupts (or releases) from the follicle. This is called ovulation.
Typically, ovulation occurs two weeks after the first day of your period, but this is not true for every woman. Some women ovulate earlier or later, depending on the length of their cycle.
③ Ovulation Isn’t Always Obvious
If you’re trying to get pregnant, you may not know when you’re ovulating. The signs aren’t quite as obvious as your period.
The most common indication of ovulation is the secretion of a white, sticky discharge that looks like egg whites. While this type of discharge is often a sign of ovulation, there’s a chance that the fluid can be normal discharge or even a sign of early pregnancy for some women.
One of the best ways to determine if you’re ovulating is to measure your basal body temperature. A slight increase in your body’s temperature is often an indication that you’re fertile.
④ Fertilization is a Miraculous Thing
The average ejaculate contains about 150 million sperm. The job of the sperm is to swim up the fallopian tube, and fertilize the egg. They only have about 12-48 hours to tackle this task before they die.
Only about 85% of sperm will reach the fallopian tube, and only 15% will make it all the way up to the egg. When all is said and done, only about 1,000 sperm are left to fertilize the egg, and they not only have to find their way to the egg – they also have to pick the right fallopian tube. But only one sperm will fertilize an egg.
⑤ Once Fertilized, the Egg Changes
All it takes is just one sperm to fertilize an egg, and when it does, it burrows into the egg. After this happens, the egg begins to change to prevent other sperm from trying to get in and fertilize.
As soon as the egg is fertilized, the baby’s sex and genes are set. Sperm with an X chromosome will produce a baby girl, while sperm with a Y chromosome will produce a baby boy. Within 24 hours, the egg starts quickly dividing into many cells.
⑥ Implantation Occurs in the Uterus
A fertilized egg will stay in the fallopian tube for 3-4 days. During the first few days of fertilization, the egg, as its dividing, will move slowly down through the fallopian tube and into the uterus.
Once it arrives in the uterus, the egg will burrow itself into the wall of your uterus. This is known as implantation.
⑦ Implantation May Cause Light Bleeding
Implantation can cause very light bleeding and cramping. As the egg burrows into the uterine wall, it may cause some shedding and bleeding as a result (similar to what happens when you get your period).
Light bleeding is normal during implantation, but if you notice a heavy flow or the bleeding lasts more than a few days, you may have had a miscarriage, or your period may have come.
⑧ Implantation Usually Occurs 6-10 Days after Ovulation
If a sperm successfully fertilizes an egg, it will take up to 10 days for implantation to occur, depending on when the egg was fertilized and the length of your cycle.
For women with a 28-day cycle, ovulation usually occurs on the 14th day after your last period started. It takes about three days for the egg to make its way into the uterus.
⑨ Implantation Isn’t Always Successful
Even if a single sperm manages to fertilize the egg, there’s no guarantee that implantation will be successful. About three-fourths of lost pregnancies are caused by failed implantation, so it’s not uncommon.
Implantation is a sticky process – literally. The early embryo expresses a type of protein known as L-selectin, and at the same time, the uterus is enriched with carbohydrates. The L-selectin protein binds with carbohydrates briefly, which creates a sticking and unsticking interplay between the uterus and egg. This process slows down the embryo’s progress as it moves along the uterine wall.
Once the embryo rests, it has the chance to burrow into (or attach to) the uterine wall. At this point, the embryo starts gaining nourishment from the placenta, and pregnancy can begin.
⑩ Miscarriages Are Common Even After Implantation
While a large percentage of miscarriages are caused by failed implantation, other factors can lead to a lost pregnancy even after implantation has occurred.
According to doctors, mismatched chromosomes account for 60% of early miscarriages. Every one of us has a pair of 23 chromosomes – one from our mothers, and one from our fathers. When the egg and sperm meet, there’s a chance that the chromosomes don’t match up properly or one is faulty. When chromosomal abnormalities occur, the pregnancy typically results in a miscarriage.
Miscarriages can also occur if you have issues with your cervix or uterus. Thyroid problems, uncontrolled diabetes and other medical issues can lead to miscarriages as well.
Even if implantation does occur, there is a chance that your pregnancy can end in miscarriage early on. While devastating, this is not an uncommon occurrence.