Implantation or Nesting, Symptoms of an Embryo Implantation

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The crucial moment in any pregnancy attempt, whether natural or obtained through assisted fertilization techniques, is the implantation of the embryo in the uterine wall: this phenomenon is called implantation or nesting.

For this reason, many women try to understand which symptoms can indicate a successful implantation and therefore when they can feel fairly certain that they have entered the pregnancy phase.

Generally, the nesting phase of the embryo does not coincide in time with fertilization, but follows it by 6-7 days up to even 10 days. This is just the time needed for the fertilized egg to travel the distance from the tube to the uterus. Therefore, much will depend on the day of ovulation and the regularity of the menstrual cycle, making this time window extremely dependent on the individual woman.

The entire delicate phase of pregnancy is characterized by very precise temporal phases, right from the beginning. The sperm, for example, has only 24 hours to fertilize the egg (this being the lifespan of a female egg). Once conception has occurred, the zygote will begin the replicative phases that will bring it to the blastocyst stage within 5 days. Meanwhile, hormones prepare the endometrium to make it suitable for nesting.

In this case, too, there exists the so-called implantation window or WOI, lasting about 72 hours, during which the uterus has the highest receptive capacity and therefore the highest probability of achieving correct nesting.

This phase can be identified by our Fertilab laboratories, in the case of assisted fertilization techniques, through endometrial receptivity tests.

The implantation process is complicated not only in terms of timing but also in its modalities, and can be divided into 3 distinct phases:

  1. Adplantation: the embryo physically attaches to the uterine endometrium;
  2. Penetration: after attachment, it delves into the wall thickness;
  3. Finally, it incorporates deeply, from which it will then progressively grow.

From this point on, the production of beta hCG will also begin, essential for fetal growth and whose detection will give us certainty of pregnancy.


What are the symptoms of embryo implantation

One should always start from the assumption that every woman is unique, in which there can be a whole series of characteristic symptoms or she can even be completely asymptomatic even if pregnant.

In any case, when these are present, they can also be quite typical, enough to strengthen the initial hypothesis. In most cases, we can observe:

  • Small brown or reddish blood losses (called implantation losses) due to the penetration of the embryo into the uterine wall, which, being excavated, will lose blood. Often, women can confuse these losses with normal menstruation, also because of the temporal plausibility of the same, but generally, implantation losses are considerably reduced in quantity and disappear completely within a maximum of 2-3 days;
  • Swelling and slight abdominal cramps;
  • Possible dizziness;
  • Need to urinate more frequently;
  • Breast tension;
  • Slightly high basal temperature.
  • Once implantation has successfully occurred, the embryo and later the fetus will “feed” directly from the mother, as this is where the so-called epigenetic exchanges occur, a topic still being explored by scientists.


How reliable is the use of pregnancy tests in utero implantation?

Usually, Fertilab Barcelona clinic professionals specialized in assisted reproduction recommend taking the pregnancy test 14 days after embryo fertilization, while if it is artificial insemination, 14 days after ovulation. If, on the other hand, one has opted for in vitro fertilization, it will depend on the day the embryo transfer was done (for example, if it was on day +3, you can take the test 11 days after the transfer).

In any case, the most reliable test remains the search for the beta hCG hormone in the blood: if the level is low, the prognosis is not encouraging, but a normal pregnancy cannot be ruled out with certainty. For this reason, in fact, it is possible to repeat the tests after a few days and if, in this second test, we observe adequate levels of beta hCG, then an ultrasound can be scheduled.

The ultrasound is an extremely important tool, as during the fifth week the gynecologist will already be able to observe the embryonic sac and thus exclude a possible ectopic pregnancy. After 10 days, a second ultrasound will be performed to verify the presence and correct heartbeat, thus confirming with absolute certainty the pregnancy.


What happens if implantation does not occur?

It is a widespread belief that the un-implanted embryo is automatically expelled with the subsequent menstruation. However, this is a misconception, as it will be reabsorbed by the mother’s body and thus disappear.

The Fertilab team makes its specialists fully available to all patients to be able to frame the pregnancy and recognize its symptoms, especially if as a result of medically assisted fertilization.

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