When Does Implantation Occur?

During the reproductive years, a woman's body goes through several physiological changes. A woman's ability to conceive and support a pregnancy is linked with the cyclical changes that are associated with menstruation. Conception, which is also called fertilization, is the stage in which the egg is fertilized by the sperm.

The process of fertilization takes around 24 hours. This is followed by the division of the egg into many cells. Implantation is a process in which the fertilized egg attaches itself to the uterine wall. After the egg and sperm get fertilized in the Fallopian tube, the fertilized egg usually takes three days to leave the Fallopian tube and enter the uterus.

After that, the egg attaches itself to the endometrial lining. Implantation of the fertilized egg normally occurs 6 to 12 days after ovulation. It may occur between day 20 to 23 of the menstrual cycle. The time at which the fertilized egg attaches itself to the endometrial lining may vary depending on the length of the menstrual cycle.

On an average, the length of monthly menstrual cycle is considered to be 28 days. However, it can range from 28 to 35 days.

Menstrual flow, thickening of uterine lining and ovulation are physiological cyclical changes that occur due to changes in the levels of estrogen and progesterone hormone. Ovulation, which refers to the release of a mature egg, occurs two weeks after the last period.

In case of a 28-day cycle, ovaries release one mature egg (ovum) on the day 14. This egg then travels from ovaries into the uterus, through the Fallopian tube. For a woman to get pregnant, the egg must fuse with a feasible sperm. If that happens, then they get merged to form a diploid cell zygote. This zygote, then gets transformed into a blastocyst.

First day of the period is considered to be first day of the menstrual cycle, and the fertilized egg gets implanted occurs a week before the start of the next cycle. If the process of fertilization doesn't take place or the fertilized egg doesn't get implanted, then the blastocyst is discharged out of the body through menstruation.

'In vitro fertilization' (IVF) is the process of fertilization of egg by the sperm, outside the body. It is a technique suggested for women who are unable to conceive despite trying for a year. There are 5 main stages of IVF. These include ovarian stimulation, egg retrieval, fertilization, culture and selection of the embryo quality, and embryo transfer.

In case of IVF, post embryo transfer stage is the actual stage that confirms the viability of IVF. The egg gets implanted after 6 to 12 days of egg retrieval. The egg reaches the blastocyst stage, after 5 days of embryo transfer; which can take place on different days of its development, hence, for accurate results, count the day of egg retrieval as day 0.

Women may experience mild spotting and cramping once the fertilized egg attaches itself to the uterine wall. Trophoblasts are the outer layer of the cells or specialized tissue of the blastocyst that form the placenta.

When the specialized tissue attaches itself to the uterine lining, it can rupture tiny blood vessel of the uterus which in turn may give rise to spotting or slight bleeding. This is called implantation bleeding. This is different from the regular menstrual flow.

Not every woman experiences bleeding during pregnancy. Those who do, may experience bleeding 7-10 days after fertilization. It could last for a few minutes to even for a week. In case of women who have opted for IVF, bleeding may take place a week after egg retrieval.

Implantation bleeding is one of the early signs of pregnancy. If it is accompanied with other pregnancy symptoms like morning sickness, tender breasts, food aversion and raised basal temperature, then it is definitely the best time to take a pregnancy test. Always remember to take the pregnancy test two to three days after you experience such symptoms.