Miscarriages and implantation failures

We speak of recurrent miscarriages when at least two pregnancies have ended in miscarriage.

We speak of implantation failure when a patient has not achieved pregnancy after several good quality embryo transfers.

We consider the same origins for recurrent miscarriages and implantation failures. In case of implantation failures the alterations are produced before the embryo development inside the uterine cavity has started.

What are the reasons for miscarriages and implantation failures?

The main reasons for miscarriages and implantation failures are:


This is the most frequent reason for recurrent miscarriages and implantation failures. Genetic alterations of the embryos might provoke that they do not implant or that the pregnancy ends in miscarriage.

Many of the embryos with genetic abnormalities can develop just normal in the laboratory which makes the only way to identify them using preimplantation genetic diagnosis.



Most important uterine reasons for recurrent miscarriages and implantation failures are:

  • Chronic infections of the endometrium without symptoms
  • Alterations of the uterine cavity such as polyps, myomas, divisions or adhesions
  • Alterations in the endometrial receptivity through abnormalities in the implantation window. This window is the period of time in which the endometrium, thanks to the progesterone, permits the implantation of the embryo. Its duration is of two to six days.

Antiphospholipid syndrome:

With the antiphospholipid syndrome the mother produces antibodies, which might affect the placenta through the phenomenon of thromboembolism where the invasion of uterine tissue, meaning the trophoblast, in the moment of implantation of the embryo is impeded and consequently leading to the loss of the pregnancy.

Alterations in coagulation:

Thrombophilia increases the risk of thrombosis, which would affect the placentation process of the pregnancy and might end in miscarriage. Occasionally these alterations are produced very prematurely so the implantation of the embryo is ineffective.


To have an ongoing pregnancy it is necessary that the so-called “immunological tolerance” is produced permitting the woman to carry during nine months a baby in her womb without her body considering it a foreign body and attacking it. Any alteration in this immunological reaction of the woman could provoke an implantation failure or a miscarriage.


Certain hormone alterations, especially of the thyroids might be associated with recurrent miscarriage problems.

How are the causes for miscarriage or implantation failure diagnosed?

The study of recurrent miscarriages and implantation failures must include the following diagnostic tests:

Genetic analysis of the couple:

  • Karyotypes: to determine the chromosomal formula of the couple. A normal female Karyotype is 46XX and for men 46XY
  • Chromosomal study of the sperm: with the FISH technique a study can be done for five chromosomes which are frequently related with miscarriages and implantation failures if alterations are shown.


To exclude alterations of the uterine cavity.

Antiphospholipid antibodies:

This includes a study of anticoagulant antibodies for Lupus, anticardiolipin and B2- Glycoprotein.


Study of relevant factors for the mechanism of coagulation. Can be done in blood or saliva sample.

Endometrial study:

An endometrial biopsy is taken in a determined phase of the cycle in which we can carry out the following tests:

  • Endometrial receptivity: study of the implantation window to confirm that the endometrium is receptive in the moment of embryo transfer
  • Determination of NK cells: study of certain levels of inflammatory cells interfering with the implantation
  • Endometrial cultures: to exclude infections without symptoms in the endometrium.

Hormone testing:

  • Study of ovarian reserve might give indication towards egg problems
  • Thyroid blood tests includes analysis of TSH and T4L hormones.