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Conception 101: When does it happen?

by Dr. Tessa Commers
Julie Medical Advisor
After SexGeneral Sex

“Conception" gets thrown around a lot when it comes to pregnancy, but it has a very specific meaning in the medical world. Conception is also known as fertilization. But even if conception (or fertilization) occurs, it doesn't automatically mean that you're pregnant. It’s just one part of the multi-step process of becoming pregnant, which starts with ovulation and ejaculation and then concludes with a successful implantation.

Read on to learn what conception is, the additional steps that lead to pregnancy, and when to take a pregnancy test.

What is conception?

In medicine, conception is the term used to describe the merging of the egg and sperm in the fallopian tube. It’s also known as fertilization. In order for this to happen, an egg has to be released from an ovary during ovulation and sperm must travel through the vagina and uterus.

After conception, the now-fertilized egg (called an embryo) must successfully implant in the uterus for a pregnancy to begin. However, there are a variety of reasons why implantation does not happen, and the embryo will pass out of the uterus on its own. About 50% of embryos don’t implant in the uterus. It’s also possible for the embryo to briefly attach and then detach shortly thereafter, something called a chemical pregnancy. This may look like a slightly delayed period with a little more bleeding than normal.

How does a pregnancy start?

Pregnancy begins when the embryo, which is formed when the sperm fertilizes the egg, successfully implants in the uterus and then continues to grow and develop.

Timing is everything when it comes to pregnancy. Here's the breakdown of the steps that are essential for a pregnancy to happen:


Ovulation takes place in between your periods and refers to the process where a mature egg is released from the ovary into the fallopian tube. Once released, the egg can survive for 24 hours.

If you have a 28-day cycle, ovulation generally occurs around day 14. But every woman's cycle is different, and the exact day of ovulation can differ for any number of reasons.

If you track your menstrual cycle, you may have a rough estimate of what days you're ovulating. There are some symptoms that can help you tell if you’re ovulating, such as cramping, changes in body temperature, or cervical mucus.

Fact: For conception to happen, ovulation needs to occur.


Fertilization is the fusion of an egg and sperm within the fallopian tube.

Following ovulation, an egg travels to the fallopian tube. An egg is capable of fertilization for only 12 to 24 hours after ovulation, so the presence of sperm is essential for fusion to happen there. Sperm reaches the fallopian tube by traveling through the vagina and cervix into the uterus and, finally, into the fallopian tube. Each single ejaculation contains millions of sperm, and it only takes minutes for the sperm to travel from the vagina to the fallopian tube.


Implantation is when the embryo attaches to the uterus. This usually happens about 7 days after fertilization. At this point the cells of the embryo have divided (through a process called mitosis).

When does implantation occur

Implantation happens about 7 days after fertilization.

Pregnancy timeline based on a 28-day menstrual cycle

Since it's difficult to know when you're ovulating, the cycle is based on a more obvious signal: the start of your period. The timeline begins on the first day of your period and ends on the day before the start of your next period. Ovulation occurs around the midpoint between your two periods.

Here's an example of what it might look like if you were to estimate the conception and pregnancy process on a 28-day cycle:

Day 1: First day of your period (AKA, you’re bleeding)

Around day 14: This is where ovulation occurs, and an egg is released. Usually, in the middle of the cycle.

Within 24 hours of ovulation: Conception may occur if sperm is present and fertilizes an egg. This creates an embryo.

About 5-6 days after conception/fertilization: Once the embryo has reached the blastocyst stage, it may attach to the uterine lining.

When to take a pregnancy test

At-home pregnancy tests work by detecting a hormone present in your urine known as human chorionic gonadotropin (hCG). Also known as the "pregnancy hormone," hCG levels increase after the embryo has implanted onto the uterus.

Home tests differ in how early they can detect a pregnancy. Some tests can detect a pregnancy 10 days after conception. If taken too early, it may show an incorrect result. For a more accurate result, wait to take the test until you notice your period is late or missed.

What if I don't want to get pregnant?

If you have sex regularly and don't want to get pregnant, use a regular form of birth control like the daily pill, IUD, ring, shot, implant, or patch. Barrier methods can also help prevent pregnancy, and they have the added benefit of helping to protect you from giving or contracting STIs.

If you had unprotected sex and want to prevent conception and pregnancy, use emergency contraception, like the morning-after pill, as soon as possible. Julie (levonorgestrel) tablets 1.5 mg and other morning-after pills can help prevent pregnancy up to 72 hours (3 days) after unprotected sex, but they’re most effective the sooner you take them. Morning-after pills are available at Walmart, Target, and retail pharmacies like CVS and Walgreens. They're legal in all 50 states and FDA-approved. No prescription, credit card, or ID is required for purchase.

Although the information above may be useful, it shouldn’t replace the advice of your healthcare professional. For questions about birth control and other women’s health issues, please talk to your healthcare professional.