Fertilization, Process & When It Happens

How does conception take place?

Fertilization (or fertilization) is when sperm and an egg join together. This is one of the many steps that happen to create a pregnancy.

Conception is closely related to a person’s menstrual cycle. A menstrual cycle describes the sequence of events that occur in your body as it prepares each month for the possibility of pregnancy. Women or people assigned female at birth (AFAB) ovulate during their menstrual cycle. Ovulation is when your ovary releases an egg for fertilization. Small finger-like structures called fimbriae help guide the egg through your fallopian tubes to your uterus. During this journey through your fallopian tubes, an egg can be fertilized by sperm.

Sperm production begins in the testicles of men or people assigned male at birth (AMAB). During ejaculation, millions of sperm cells are released with the sole purpose of finding an egg to fertilize. When you have unprotected sex, sperm cells swim up through your vagina and into your fallopian tubes. Millions of sperm struggle to reach and penetrate the egg, but only one breaks through the egg’s outer layer to fertilize it. If sperm does not fertilize an egg, the egg dissolves.

If a sperm is successful in its quest to fertilize an egg, the now-fertilized egg (called a zygote) continues to travel down your fallopian tube, dividing into two cells, then four cells, then more cells . About a week after the sperm fertilizes the egg, the zygote has traveled to your uterus. It is now a growing group of about 100 cells called a blastocyst.

The blastocyst then attaches itself to the lining of your uterus (the endometrium). This attachment process is called implantation. However, just because fertilization occurs does not mean that implantation will. Sometimes implantation does not occur, and you pass the fertilized egg in your next menstrual period.

If implantation occurs, the cells continue to divide – some cells develop into your baby and others form the placenta. You start releasing hormones that tell your body that a baby is growing in your womb. These hormones also signal the uterus to retain its lining rather than shed it. This means you won’t get your period, which may be the first way you know you’re pregnant.

Timeline of getting pregnant

You calculate your menstrual cycle from the first day of menstrual bleeding to the beginning of the next first day of menstrual bleeding. Most menstrual cycles are about 28 days long. The exact time you ovulate varies depending on how long your menstrual cycle is.

The process of getting pregnant in a 28-day menstrual cycle is:

day one: First day of your period.
Around day 14: Ovulation occurs.
Within 24 hours of ovulation: Sperm fertilizes an egg (fertilization occurs).
About six days after conception: The fertilized egg is implanted in your uterine lining.
Around day 21: If fertilization and implantation occurred during this menstrual cycle, you are pregnant. However, it can take another five to seven days to get a positive pregnancy test.

Conception and a positive pregnancy test

After fertilization, a fertilized egg travels through your fallopian tubes to your uterus. The fertilized egg (called an embryo) implants (attachs) in the wall of your uterus. This causes the placenta to form. Your placenta starts producing human chorionic gonadotropin (hCG) and releases it into your blood and pee. HCG can be found in a person’s blood about 11 days after conception. It takes slightly longer for hCG to show up on home pregnancy tests (which measure hCG in pee).

What are my chances of getting pregnant?

Just because an egg and sperm are close together does not mean that fertilization will occur. In general, conception occurs only 25% to 30% of the time. This percentage decreases once you reach the age of 35.

How does fertilization work with IVF?

Conception still works the same way – sperm must fertilize an egg. However, with in vitro fertilization (IVF), sperm fertilizes an egg in a laboratory. An egg, either from the intended parent or a donor, is mixed with sperm from a parent or donor. Fertilization occurs when sperm fertilizes the egg.

Once conception occurs, your provider places the created embryo inside the uterus that will carry the pregnancy for implantation.

When does fertilization occur?

Fertilization occurs between 12 and 24 hours after ovulation. It is sometimes difficult to pinpoint ovulation, so using ovulation predictor kits or tracking your menstrual cycle on a calendar can be helpful. The two biggest factors in conception are:

The timing of intercourse with ovulation.
Egg and sperm health.

When should I have sex to get pregnant?

Conception can occur after unprotected sex as early as five days before ovulation. This is because some sperm can live so long inside female reproductive organs.

If you are trying to conceive, the best times to have sex are:

In the three days before ovulation: In this scenario, sperm will “wait” for the egg to come down the fallopian tube.
At ovulation or within 24 hours after ovulation: Your egg only lives for 24 hours, so if you have unprotected sex during this time, your egg may end up “waiting” for sperm to reach it, or they may meet in your fallopian tubes.

Where does fertilization take place?

Fertilization usually occurs in your fallopian tubes. This is where an egg goes after it leaves your ovary and where sperm wait for an egg. In some cases, fertilization can occur in your uterus once your egg has left your fallopian tubes.

What things prevent conception from happening?

Certain health conditions can affect your ability to conceive. Just because the sperm and egg meet does not mean that fertilization will occur. Some of the most common factors are:

Anovulation (you don’t ovulate).
Low sperm count or problems with sperm motility (how sperm move).
A blockage in the testicles, ovaries or fallopian tubes.
Decreasing quantity of quality eggs and quality sperm (usually related to aging).

Can you feel conception?

Not usually. You may notice signs that you have ovulated, such as changes in your cervical mucus or basal body temperature. However, most people do not feel conception. You may feel a dull ache or experience light spotting a few days after conception. It could be from the fertilized egg implanted in your uterus.

When do you start feeling pregnant?

How long it takes to “feel” pregnant varies. Some people may start to feel pregnant soon after conception, while others have no pregnancy symptoms weeks after a positive test.

Common signs of pregnancy are:

A missed period.
Frequent urination.
Feeling tired.
Nausea.
Sore or swollen breasts.
Spotting (light vaginal bleeding).
Headaches.
Mood swings.

Take a home pregnancy test if you have any of the above symptoms and think there is a chance you may be pregnant. Your healthcare provider may order a blood test to confirm pregnancy.

Are conception and fertilization the same?

Conception and fertilization are two different parts (or steps) of the same process. Fertilization is the first step, where an egg and sperm come together. Fertilization is another step, where the combined sperm and egg plant like a seed in your uterine lining.

How long after conception will my pregnancy test be positive?

It can take between 11 and 14 days after conception to get a positive pregnancy test. At home pregnancy tests look for human chorionic gonadotropin (hCG), a hormone released by the placenta. Your pee must have enough hCG to get a positive pregnancy test. However, your health care provider may check for hCG in your blood sooner — about 10 days after conception.

A note from Cleveland Clinic

Fertilization is when sperm fertilizes an egg. This is one of the many critical steps in conceiving. Conceiving a child is a complex process that depends on many factors. Not getting pregnant is a common problem, and there are many resources available to help you. Contact your health care provider if you are having trouble conceiving. They can explain the process and identify any problems preventing conception and pregnancy.