Implantation
The process by which a fertilized egg attaches to the lining of the uterus, beginning early pregnancy.
Implantation usually happens about a week or so after ovulation. It is the point at which the placenta begins to form and hCG starts to be produced.
After fertilization, the developing embryo travels through the fallopian tube and into the uterus. Over the following days it attaches to the uterine lining in a process called implantation. Once implantation is underway, cells that will form the placenta begin producing human chorionic gonadotropin (hCG), the hormone detected by pregnancy tests.
Why it matters for fertility awareness
Implantation marks the transition from a possible cycle event (fertilization) to an established early pregnancy that can be detected by a test. Timing varies, but it generally occurs within roughly a week or so of ovulation. This is why most home pregnancy tests work best around the time of a missed period.
How it relates to NFP
NFP charting cannot directly observe implantation. What charting can show is a luteal phase that runs longer than usual, with sustained high temperatures, which can be an early reason to consider a pregnancy test. Confirmation comes from the test, not the chart.
What it does not mean
- Symptoms alone cannot reliably confirm or rule out implantation.
- Spotting around the expected time of a period has many possible causes; treating it as definitive implantation bleeding is not supported.
- Concerns about early pregnancy, bleeding, or pain should be evaluated by a clinician.
Related terms
- hCG, /glossary/hcg
- Luteal phase, /glossary/luteal-phase
- Progesterone, /glossary/progesterone
- Ovulation, /glossary/ovulation
Related reading
- Can NFP help you get pregnant, /questions/can-nfp-help-you-get-pregnant
- The science of cycle tracking, /guides/science-of-cycle-tracking