After conception when does implantation occur?

The journey from conception to implantation consists of the following key processes:

  • Ovulation
  • Rise of hormone levels
  • Journey of the egg to the fallopian tube
  • Fertilisation
  • Implantation
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Each month a group of eggs starts to grow in small, fluid-filled sacs called follicles in the ovaries. Eventually during ovulation, one of the eggs erupts from the follicle, about 2 weeks before the next period. After eruption, when the egg leaves the follicle, the follicle develops into something called the corpus luteum. The corpus luteum releases a hormone that helps thicken the uterine endometrium, as a measure to get it ready for the egg for the egg to attach.

After the egg is released, it moves into the fallopian tube. It stays there for about 24 hours, waiting for a single sperm to fertilize it. All this happens, on average, about 2 weeks after the last period. If no sperm is around to fertilize the egg, it moves through the uterus and disintegrates. Your hormone levels go back to normal. Your body sheds the thick lining of the uterus, and your period starts.

However, if one sperm does make its way into the fallopian tube and burrows into the egg, it fertilizes the egg. The egg changes in an irreversible manner so that no other sperm can get in.

The Sperm Transport is also an important factor in the entire process of fertilisation and implantation.

The transport of sperm depends on several factors:

  • The sperm must be capable of propelling themselves through the environment of the female vagina and cervix
  • This environment, which is under cyclic hormonal control, must favour the entry of the sperm without destroying them(when the environment is too acidic, the sperm dies and hence cannot fertilise the egg)
  • The sperm must possess the capability of converting to a form that can penetrate the cell membrane of the egg (a phenomenon known as capacitation).

Following ejaculation, the semen forms a gel that protects it from the acidic environment of the vagina. The gel is liquefied within 20 to 30 minutes by enzymes from the prostate gland. This liquefaction is important for freeing the sperm so that it can travel to fertilise the egg in the fallopian tube. The seminal plasma is then left in the vagina.

The protected sperm with the greatest motility then travels through the layers of cervical mucus that form the barriers to the entrance of the uterus. During ovulation, this barrier becomes thinner and changes its acidity, creating a friendlier environment for the sperm. The cervical mucus acts as a reservoir for extended sperm survival.

Once the sperm has entered the uterus, contractions help propel the sperm upward into the fallopian tubes. The first sperm enter the tubes minutes after ejaculation. The first sperm to enter is however not the most likely one to fertilize the egg. Motile sperm can survive in the female reproductive tract for up to five days.

At the instant of fertilization, the baby's genes and sex are set. If the sperm has a Y chromosome, it will be a boy. If it has an X chromosome, the baby will be a girl.

Implantation is when a fertilized egg, or blastocyst, has attached to the lining of the uterine wall. It marks the beginning of pregnancy. The most noted members of the medical community, including the FDA, the American College of Obstetricians and Gynecologists, and the National Institutes of Health agree in unision that a woman is not considered to be pregnant until implantation has occurred. So, medically speaking, successful implantation equals the start of a pregnancy.

Hence, the process of implantation comprises of a few basic steps in short,

  • After having sexual intercourse, the sperm will travel through the vagina, in past the cervix and up to the fallopian tubes. This is where the sperm will most likely join with an available egg.
  • So, the next step is conception. This is when the sperm joins the egg and fertilization takes place.
  • About 7-14 days after having sexual intercourse, that implantation will occur—the fertilized egg will attach itself to the lining of your uterus. About 1/3 of women will have some bleeding when implantation takes place.
  • It is at this moment onwards that a considered to be pregnant.
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