What is implantation and when does it happen?
Implantation is usually considered the beginning of pregnancy. Fertilization takes place before implantation and occurs when the sperm joins with the egg. Implantation occurs when the fertilized egg (called the blastocyst or embryo) attaches itself to the wall of the uterus.
On average, implantation takes place 9 days after ovulation/fertilization or 9dpo. It normally takes between 6-12 days for the developing embryo to reach the uterus and attach to the uterine lining. At this early stage of prenatal development, the embryo is often called a blastocyst.
For in-vitro fertilization (IVF)
In IVF pregnancy, days are usually not indicated by days after ovulation dpo, but by [x]dp[y]dt. which is x days after transfer of a y day embryo transfer. So, if implantation happens on average on 9dpo, then with IVF pregnancies it happens on 4dp5dt: 4 days after a 5-day embryo transfer or 6dp3dt which is 6 days after a 3-day transfer.
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What happens with the pregnancy hormone hCG during implantation?
As soon as the blastocyst implants, it emits the pregnancy hormone hCG (or human chorionic gonadotropin) into the mother's bloodstream.
The hCG can first be detected in the blood about 3-4 days after implantation, and this is when a positive blood test can confirm a pregnancy. The urine pregnancy test becomes positive 1-2 days later. That is often several days before you expect your next period or around the time of a missed menstrual period.
This implantation calculator will give you the days you may likely experience implantation. It will also let you know when you can expect a pregnancy test to be positive.