Implantation and the Start of Pregnancy

Implantation is when a fertilized egg, or blastocyst, has attached to the lining of the uterine wall. It marks the beginning of pregnancy. The medical community, including the American College of Obstetricians and Gynecologists and the National Institutes of Health, agrees that a person is not pregnant until implantation has occurred. Medically speaking, successful implantation (not fertilization or conception) equals the start of a pregnancy.

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: Seven to 14 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 one-third of women experience bleeding with implantation. At this point, pregnancy has officially begun.

If implantation does not take place, the fertilized egg will leave the body, probably during your period. Conception does not automatically equal implantation or pregnancy.

Implantation and hCG

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.

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  1. Cleveland Clinic. Pregnancy: Ovulation, conception and getting pregnant. Updated February 19, 2019.