Take our Fertility Quiz and get 10% off!

Take our Fertility Quiz and get 10% off!

Fertilization vs Implantation: The Breakdown of Both & When They Occur

Written by:, PhD, Founder and Inventor of the Proov test — the first and only FDA-cleared test to confirm successful ovulation at home.

An incredible amount of things occur in the first week of pregnancy! We’re going to break down exactly what’s happening and when, so that you’ll feel informed before you even get a positive pregnancy test. (We’ll let you know when to take one of those, too!) 

The Conception Timeline Explained 

Here’s a quick overview of the conception timeline before we break it down: 

It takes about 2 weeks from the start of your period for the ovary to prepare an egg for ovulation. If sperm are present when ovulation occurs – about midway through the menstrual cycle –  it’s possible for one sperm to fertilize the egg, forming an embryo. 

After fertilization occurs, the new embryo has to travel to the lining of the uterus to implant. This typically takes 6-10 days. 

Once the embryo implants, it will slowly start creating the placenta, where it will eventually receive all of its nutrients and life support through the mother’s body. At the same time, the embryo begins producing the hormone hCG (human chorionic gonadotropin). 

At least 2-3 days after hCG begins, you can get a positive pregnancy test!

Ovulation & Conception

When it’s time for a new egg to ovulate, recruitment begins near the start of a menstrual cycle, and causes the egg’s protective follicle to begin producing rising levels of estrogen. Estrogen is the dominant hormone during the follicular phase of the menstrual cycle.

Estrogen is responsible for thickening the lining of the uterus, as well. Both are essential for a possible pregnancy. 

When the follicle around the egg has reached a mature size and the estrogen has reached sufficient levels, it signals the brain to produce LH (luteinizing hormone) which helps the egg to leave the follicle and the ovary through the process called ovulation. There are at-home tests that allow you to test for the surge of LH and know when ovulation is about to happen!

Once the egg has ovulated, it could be fertilized by a sperm and conception may occur. 

What is the Fertilization Process? 

Once the egg ovulates, it makes its way to the fallopian tubes. These tubes connect to the uterus, which is the egg’s final destination. But it’s possible for the egg to encounter sperm along the way. 

When sperm enter the female reproductive system during her fertile window, they have the ability to travel throughout the reproductive system to wait for ovulation to occur. That means that they can be found hanging out in the fallopian tubes for up to 5 days to try to catch that egg! 

The egg only lives about 12-24 hours once ovulated, so time is of the essence. Thousands of sperm can be waiting for ovulation, and if they’re there at the right time, they will all descend on the egg in an attempt to fertilize it. But only one sperm can successfully fertilize the egg. When that sperm enters the egg, the enzymes change and an embryo is created!

This is the fertilization process, also known as conception. 

When does implantation occur? 

Thousands of things have to go right for a pregnancy to be successful, but the first main event after a successful fertilization is implantation. Implantation is the process of the embryo burrowing into the lining of the uterus in order to attach for the remainder of the pregnancy. That’s right: wherever the embryo attaches will be where the placenta grows and the baby stays throughout pregnancy! 

In order for implantation to occur, the lining of the uterus must be well prepared. While estrogen is the dominant hormone during the pre-ovulatory (or follicular) phase, progesterone is the dominant hormone during the post-ovulatory phase, called the luteal phase. Progesterone is responsible for stabilizing the already thick uterine lining and making it “sticky” enough so that an embryo can successfully implant.

The follicle that ovulated the egg and produced the estrogen is now producing progesterone. Knowing your progesterone levels are sufficient during the implantation window can help ensure the lining of the uterus has been prepared to allow an embryo to implant. You can test PdG (progesterone metabolite) levels during the implantation window with Proov Confirm

This can even occur while the embryo is traveling to the uterine lining, because it takes 6-10 days to make its way there from the fallopian tubes where the fertilization process occurred. 

Is it time to take a pregnancy test? Not quite! It still takes several days for an implanted embryo to begin producing detectable amounts of hCG, the hormone a pregnancy test needs for a positive result. (This is also why it’s possible to have a false negative, if you test too early.) 

Signs and Symptoms of Implantation

If it’s too early for a pregnancy test, but you’re wondering if you could be pregnant, you could always have some fun looking at any signs and symptoms of implantation. We can’t say that the presence or absence of these symptoms reveals whether or not you’ve conceived (the pregnancy test will tell you that!), but it can still be fun to check them out! 

When the embryo implants in the uterine lining, you may notice

  • Breast tenderness 
  • Headaches
  • Lower back pain
  • Mild cramping
  • Mood swings 
  • Nausea 
  • Implantation bleeding 

While implantation bleeding may feel like the easiest sign to interpret, it only occurs in about a third of pregnancies. So if you don’t experience implantation bleeding, or any of the other implantation symptoms listed, it doesn’t mean you haven’t conceived. It could mean that it’s too early, or that you don’t have symptoms with your implantation. 

It’s also worth mentioning that it’s possible for the embryo to implant outside of the uterus, most frequently in the fallopian tube. This is called an ectopic pregnancy, and the location of implantation will restrict the embryo from growing and thriving. Severe cramping, dizziness/weakness, or a pregnancy that can’t be found within the uterus (during an ultrasound) may all point to the possibility of an ectopic pregnancy. If you are concerned about ectopic pregnancy, we absolutely recommend consulting your doctor. 

How to Know You’re Pregnant

The process to get to pregnancy is involved and amazing! But by the end of that two week wait, you’re ready to know one way or another! The easiest way to do this is by taking an at home pregnancy test, which reads the amount of hCG (that hormone created by the implanted embryo!) in your urine.

We recommend waiting until the embryo has had time to implant and create hCG, which is usually around 10-14 days after the LH surge. If you see any color in the test line, it’s time to call the doctor to confirm! 

Want to test all the important hormones when it comes to getting pregnant? Try Complete!

Have questions? Email us!