Implantation and the Start of Pregnancy

Implantation is when a fertilized egg, or blastocyst, attaches to the lining of the uterine wall. After implantation happens marks the beginning of pregnancy. In fact, the medical experts like the American College of Obstetricians and Gynecologists and the National Institutes of Health agree that a person is not officially pregnant until implantation has occurred.

Implantation occurs eight to 10 days after fertilization. At this point the embryo moves out of the Fallopian tubes and into the uterus, where it burrows into the uterine wall. After implantation, the embryo will continue to grow and develop until it becomes a fetus, 9 weeks after fertilization.

Medically speaking, successful implantation (not fertilization or conception) equals the start of a pregnancy. Learn more about implantation, what happens after implantation, and the early days of gestation.

The Implantation Process

Here's where implantation fits in the journey to pregnancy.

1. Ovulation: In order to become pregnant, you need to ovulate (release an egg from an ovary into the fallopian tube).
2. Ejaculation: After sex, sperm travel through the vagina, past the cervix and up into the fallopian tubes. This is where the sperm will most likely join with an available egg.
3. Fertilization: When the sperm joins the egg and fertilizes it, conception takes place.
4. Implantation: About 7 days after sex, the fertilized egg attaches itself to the lining of the uterus. This is implantation.

Timing of Implantation

If you have unprotected sex anytime from about five days before to 24 hours after you ovulate, conception can happen. After conception, the process of becoming pregnant still takes several days, because the fertilized egg (now called a blastocyst) has only just begun its long journey. 

The blastocyst has to travel from the fallopian tube into the uterus for implantation to take place. As it makes this journey, it grows in size and its cells divide and reproduce.

A type of tissue called trophoblast develops from the fertilized egg and surrounds it. This trophoblast helps to implant the blastocyst once it arrives in the uterus. The trophoblast begins to push its way into the uterine lining. Next, the trophoblast actually pulls the egg inside of the uterine wall. It then directs blood to the fertilized egg.

Implantation takes place about nine days after ovulation. About 25% of women experience bleeding with implantation. At this point, pregnancy has officially begun.

What Happens After Implantation?

Implantation is the first trigger for the body to start producing hCG (human chorionic gonadotropin, also known as the pregnancy hormone). Pregnancy tests (both home urine tests and blood tests) look for the presence of hCG to confirm a pregnancy. Implantation must occur for this hormone to be produced.

If you get a positive result on a pregnancy test, then you know that implantation has taken place (since your body had started to produce the hCG hormone, and the test detected this hormone). If you take a pregnancy test before implantation occurs, the test will tell you that you’re not pregnant, even if you have actually conceived. Since hCG is not yet in your system, the test cannot detect it.