The “two week wait” between your carefully calculated ovulation and taking a pregnancy test can be very stressful, so you may be wondering: how does implantation occur? What conditions might make the egg more or less likely to settle in? And how might you know if implantation has occurred? Let’s take a look.

The Hows and Whys of Implantation

Implantation typically occurs between 6 and 12 days after ovulation, with most cases occurring around day 9. At the point where the fertilized egg enters the uterus, it’s known as a blastocyst — a round collection of stem cells in fluid with an outer layer that eventually forms the placenta. This outer layer is essential for implantation, because it is what adheres to and merges with the endometrium, or uterine lining.

In most successful implantations, the arrival of the blastocyst coincides with peak levels of luteinizing hormone (LH), which primes the endometrium to accept the embryo. In addition to LH, a chemical called trypsin produced by the embryo signals the uterine lining to prepare for implantation. A favorable endometrium is thick and exhibits a triple-line pattern under ultrasound imaging.

Unfortunately, various conditions can hamper the proper implantation of a blastocyst. In some cases, genetic disorders in the developing embryo disrupt the trypsin signal and cause a stress reaction that forces the uterus to reject the blastocyst. Immunological disorders may cause the mother’s body to attack the implanting embryo. Ultimately, implantation is a delicate process, and roughly half of all fertilized eggs fail to successfully implant.

Signs of Successful Implantation

If the embryo successfully implants, you can expect to experience a number of signs or symptoms. Unfortunately, the earliest signs of successful implantation can appear like the normal signs of a period: cramps, headaches, fatigue, and bloating. In 20% to 30% of women, they will also experience implantation bleeding similar to what they experience during a period.

Additional symptoms will follow implantation:

  • Your breasts may feel sore, tight, or tender.
  • If you continue tracking your basal body temperature after ovulation, you may notice that your average temperature has increased.
  • In fact, this rise in temperature combined with fatigue and other symptoms may make you think you have the flu.
  • Within a week of implantation, you will feel more frequent urges to urinate. This is because increased blood flow to the uterus has put pressure on your bladder.

Of course, the only way to tell if you have had a successful implantation is to take a pregnancy test. Consult with your doctor if you have any questions, and especially if the test comes back positive!

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