Embryonic implantation


Once the embryonic transfer has been completed and the embryo has been deposited at the bottom of the uterus, it’s necessary to wait about 12 days until the pregnancy test can be reliably performed. This is a waiting period which, in most cases, seems a lengthy one that’s often accompanied by nerves and impatience until the moment when the result becomes known.

It’s very common for patients to wonder if there are any symptoms, any signs to indicate whether the embryonic implantation has taken place, which would thus alleviate the uncertainty of this waiting period to an extent. 

What is embryonic implantation?

It’s the process during which the embryo adheres to the endometrium (walls of the uterus) and it’s at this moment, on the seventh day after fertilisation, that the gestation begins.  

From the moment the sperm and egg are fertilised, the embryo begins to divide and advance along the fallopian tubes until, up to 6 days later, it reaches the uterus, which is when the implantation occurs. There then begins the synthesis of the B-HCG hormone, which is the one the pregnancy test is able to detect seven days after implantation in the uterus.


Symptoms of embryonic implantation

Initially there are no symptoms that can reliably predict a pregnancy; to obtain a result it will be necessary to wait until the blood pregnancy test has been performed. 

It’s very important to bear in mind that the fact that there are no symptoms doesn’t mean an implantation hasn’t taken place. In fact, the few indicators of an implantation are very finely drawn and subjective, so it’s difficult to distinguish them from the effects of the hormonal stimulation carried out during this period.

The potential symptoms or signs of an implantation include the implantation bleeding. This can be observed in just three out of ten pregnancies. It’s less intense and lighter than menstruation and shorter in duration (as little as a few hours), the colour is more intense and darker and there are no clots.

When the embryo adheres and is implanted in the inner part of the uterus, the most superficial parts of the blood vessels burst, as it literally invades the tissue (endometrium) of the uterus. From then onwards, new connections are formed with the embryo of arteries, veins and capillaries that will allow nutrients and oxygen to be exchanged during the pregnancy. 


The blood that’s lost during this process of breaking down and generating new connections with the embryo constitutes the implantation bleeding.

In any event, the endometrium is a highly vascularised tissue and small amounts of bleeding can occur naturally for reasons other than implantation.

  • Slight swelling of the breasts
  • Drowsiness
  • Abdominal pain similar to colic or menstrual pain
  • Digestive/intestinal discomfort (heartburn, constipation or diarrhoea, among others)

As mentioned above, these are quite subjective symptoms that aren’t very obvious and not exclusive to implantation.

It’s very difficult to differentiate them from all the symptomatology caused by the medication used during the treatment and, therefore, they are by no means infallible signs that an embryonic implantation has taken place.

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