Go to Content Go to Navigation Go to Navigation Go to Site Search Homepage


How does pregnancy happen?

In order for pregnancy to happen, sperm needs to meet up with an egg. Pregnancy officially starts when a fertilized egg implants in the lining of the uterus.

How do people get pregnant?

Pregnancy is actually a pretty complicated process that has several steps. It all starts with sperm cells and an egg.

Sperm are microscopic cells that are made in testicles. Sperm mixes with other fluids to make semen (cum), which comes out of the penis during ejaculation. Millions and millions of sperm come out every time you ejaculate — but it only takes 1 sperm cell to meet with an egg for pregnancy to happen.

Eggs live in ovaries, and the hormones that control your menstrual cycle cause a few eggs to mature every month. When your egg is mature, it means it’s ready to be fertilized by a sperm cell. These hormones also make the lining of your uterus thick and spongy, which gets your body ready for pregnancy.

About halfway through your menstrual cycle, one mature egg leaves the ovary — called ovulation — and travels through the fallopian tube towards your uterus.

The egg hangs out for about 12-24 hours, slowly moving through the fallopian tube, to see if any sperm are around.

If semen gets in the vagina, the sperm cells can swim up through the cervix and uterus and into the fallopian tubes, looking for an egg. They have up to 6 days to find an egg before they die.

When a sperm cell joins with an egg, it’s called fertilization. Fertilization doesn’t happen right away. Since sperm can hang out in your uterus and fallopian tube for up to 6 days after sex, there’s up to 6 days between sex and fertilization.

If a sperm cell does join up with your egg, the fertilized egg moves down the fallopian tube toward the uterus. It begins to divide into more and more cells, forming a ball as it grows. The ball of cells (called a blastocyst) gets to the uterus about 3–4 days after fertilization.

The ball of cells floats in the uterus for another 2–3 days. If the ball of cells attaches to the lining of your uterus, it’s called implantation — when pregnancy officially begins. 

Implantation usually starts about 6 days after fertilization, and takes about 3-4 days to complete. The embryo develops from cells on the inside of the ball. The placenta develops from the cells on the outside of the ball.

When a fertilized egg implants in the uterus, it releases pregnancy hormones that prevent the lining of your uterus from shedding — that’s why people don’t get periods when they’re pregnant. If your egg doesn’t meet up with sperm, or a fertilized egg doesn’t implant in your uterus, the thick lining of your uterus isn’t needed and it leaves your body during your period. Up to half of all fertilized eggs naturally don’t implant in the uterus — they pass out of your body during your period.

What are early pregnancy symptoms?

Many people notice symptoms early in their pregnancy, but others may not have any symptoms at all.

Common signs and symptoms of pregnancy can include:

  • Missed period

  • Swollen or tender breasts

  • Nausea and/or vomiting

  • Feeling tired

  • Bloating

  • Constipation

  • Peeing more often than usual

Some early pregnancy symptoms can sometimes feel like other common conditions (like PMS). So the only way to know for sure if you’re pregnant is to take a pregnancy test. You can either take a home pregnancy test (the kind you buy at the drug or grocery store), or get a pregnancy test at your doctor’s office or local Planned Parenthood Health Center.

How do people get pregnant with twins?

There are 2 ways that twins can happen. Identical twins are made when 1 already-fertilized egg splits into 2 separate embryos. Because identical twins come from the same sperm and egg, they have the same genetic material (DNA) and look exactly alike.

Non-identical twins (also called “fraternal” twins), are made when two separate eggs are fertilized by two separate sperm, and both fertilized eggs implant in the uterus. This can happen if your ovaries release more than one egg, or during certain kinds of fertility treatments. Non-identical twins have completely different genetic material (DNA), and usually don’t look alike. They’re the most common type of twin.

What is gestational age?

The term “gestational age” basically means how far along into a pregnancy you are. Gestational age is counted by starting with the first day of your last menstrual period (called LMP).

Gestational age can be kind of confusing, since it measures pregnancy from your last period — about 3-4 weeks BEFORE you’re actually pregnant. Common knowledge about pregnancy says it lasts 9 months, and it’s true that you’re usually pregnant for about 9 months. But the way pregnancy is measured makes it a little longer. A typical full-term pregnancy ranges from 38-42 weeks LMP — around 10 months.

Many people can’t remember the exact date of their last menstrual period — that’s totally okay. Your nurse or doctor can find out the gestational age using an ultrasound.

More questions from patients:

Can you get pregnant from precum?

Your chances of getting pregnant from precum are pretty low. But it is possible.

Pre-cum is a small amount of fluid that comes out of the penis when you’re aroused, but before ejaculation happens. It doesn’t usually have any sperm in it. But some people’s pre-cum does have a small amount of sperm in it sometimes. This means sperm can get into the vagina and possibly fertilize an egg.

There’s no way to know who has pre-cum in their sperm and who doesn’t, so that’s one reason why the withdrawal method (pulling out) isn’t the best at preventing pregnancy.

If you don’t want to get pregnant, put on a condom before your genitals touch your partner’s. Even better, use both condoms and another kind of birth control together.

What are the stages of pregnancy?

Pregnancy lasts about 40 weeks. The stages of pregnancy are divided into 3 trimesters. Each trimester is a little longer than 13 weeks.

You’ll go through many changes during each trimester. Some people feel lots of discomfort. Others don’t feel much at all.

During the first trimester, you’ll probably have lots of body changes, including:

  • Tiredness

  • Tender, swollen breasts

  • Morning sickness

  • Cravings or distaste for certain foods

  • Mood swings

  • Constipation

  • Needing to pee more often

  • Headache

  • Heartburn

  • Weight gain or loss

Most of these symptoms go away when you get to the second trimester. This is when your belly gets bigger and you’ll feel the fetus move. You may also notice:

  • Body aches

  • Stretch marks

  • Darkening of your areolas

  • A line on your skin running from your belly button to pubic bone

  • Patches of darker skin

  • Numb or tingling hands

  • Itching on your abdomen, palms, and feet

  • Swelling of your ankles, fingers, or face

In the third trimester, some of the same symptoms may continue. You may also experience:

  • Shortness of breath

  • Needing to pee even more often

  • Hemorrhoids

  • Your breasts leaking a watery pre-milk called colostrum

  • Your belly button sticking out

  • Trouble sleeping

  • The baby "dropping" or moving lower in your abdomen

  • Contractions

If you aren’t sure if your symptoms are normal, call your doctor or midwife or visit your local Planned Parenthood health center.

Was this information helpful?
You’re the best! Thanks for your feedback.
Thanks for your feedback.

Had Unprotected Sex? Chat With a Health Educator Now.

Chat online or text "PPNOW" to 774636 (PPINFO) to get answers about pregnancy, birth control, emergency contraception, STDs, and abortion. 

Standard message and data rates may apply. Text STOP to quit at anytime, and HELP for info.

Chat Now