By (embryologist).
Last Update: 02/15/2019

Both infertility and sterility mean that a couple is unable to carry a child naturally. But then, are they the same, is there any difference between the two concepts? Although we use them as synonyms when talking about fertility problems, the definition of sterility and infertility is not exactly the same. Therefore, this article will clarify the confusion between the two terms.

Sterility is not the same than infertility

Sterility refers to the inability to have children due to problems in fertilization, i.e., caused by the inability of the egg and sperm to unite to form the embryo.

Infertility, on the other hand, indicates the inability to carry out gestation, that is, the absence of birth in spite of the fact that conception has taken place.

In both cases there is no full-term pregnancy, however, infertility is one step closer. In cases of sterility there is not even fertilization while in cases of infertility, the embryo is created and there may even be early embryonic development, but birth does not occur.

In a schematic way:

  • Sterility: there is no fertilization, i.e. conception does not occur. Egg and sperm are not able to form the embryo.
  • Infertility: fertilization takes place but later problems appear such as failure of the implantation or development of the embryo that prevent the pregnancy from being completed.

Sterility

Sterility can occur from different causes in both men and women. Among the most common factors of female sterility we can highlight:

  • Defects in the structure or quality of the eggs
  • Ovulation issues
  • Alterations in Fallopian tubes that make it difficult for the egg and sperm to meet
  • Functional or anatomical alterations of the cervical canal that may prevent sperm from entering.
  • Uterine factor: structural alterations such as the presence of fibroids or abnormalities, as well as endometrial alterations that can cause problems for the union of gametes.

Among the causes that lead to male sterility, the most common are:

  • Endocrine or pre-testicular factor: alterations related to the release of hormones involved in the production of sperm production
  • Testicular factor: trauma, hydrocele, varicocele, cryptorchidism..
  • Post-testicular factor: sexual impotence, retrograde ejaculation, obstruction of the sperm ducts, infections…
  • Sperm factor: quantity of sperm, low motility, abnormalities in sperm structure, etc.

Infertility

As we have seen, when a couple is infertile, fertilization does occur but it is not effective, that is, it does not allow the pregnancy to reach term.

For a baby to be born, the egg and sperm must meet, the embryo must be formed and implanted in the endometrium (external layer of the uterus) and develop during approximately 9 months in the mother’s womb until leaving the uterus in birth.

Throughout these 9 months, different events may occur that prevent the proper evolution of the pregnancy. Among these events we may highlight:

  • Implantation failures: the embryo is formed but cannot be implanted in the maternal endometrium.
  • Abortion
  • Ectopic pregnancy: the embryo implants but outside the uterine cavity

All these alterations can be produced for different reasons: immune disorders, genetic alterations, infections, uterine anomalies, etc.

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Absent Uterus

The absence of a uterus is a cause of both sterility and infertility. First of all, it is a problem of sterility because without a uterus, natural fertilization is not possible. However, it is also a problem of infertility because, even if fertilization occurs in vitro, that is, in the laboratory, the embryo created could not develop, due to the lack of uterus.

Assisted reproduction can solve both sterility and infertility problems. However, the absence of a uterus is complex. One of the possible reproductive solutions is surrogacy.

It is a process of In Vitro Fertilization (IVF) in which the embryo generated is transferred to the uterus of a woman, the pregnant woman, who will not later be the mother of the baby born. This woman simply offers her capacity to gestate to another woman, man or couple who does not have this capacity.

FAQs from users

What is the difference between primary and secondary sterility?

By Andrea Rodrigo (embryologist).

Primary sterility is when a couple has never achieved pregnancy and secondary sterility when, after having already had a child, the couple does not achieve the second pregnancy.

The same applies to infertility. Primary infertility means that the first pregnancy is not successful, while secondary infertility means that, after the birth of a first child, the pregnancy of the second ends in abortion or any other abnormality that prevents the development until delivery.

What is idiopathic sterility?

By Andrea Rodrigo (embryologist).

The term idiopathic sterility refers to unexplained fertility problems. In spite of the tests and analyses carried out on the couple, it is not possible to determine the exact cause why the fertilization of the egg does not happen.

Does chemotherapy cause sterility or infertility?

By Andrea Rodrigo (embryologist).

Chemotherapy can cause sterility as it affects the eggs and sperm. Therefore, if this oncological treatment prevents the development and maturation of the gametes, fertilization cannot occur and, therefore, we are dealing with a case of sterility.

Is sterility hereditary?

By Andrea Rodrigo (embryologist).

Sometimes sterility and infertility can be caused by a genetic alteration, so it may be inherited. It can also happen that, although a certain genetic alteration is not inherited, the fact that a parent has had fertility problems can be a risk factor for being sterile. It is possible that the predisposition of the child to suffer sterility or infertility is increased despite the fact that the cause is not directly a specific genetic alteration.

In any case, it will depend on each situation and the origin of the problem to conceive.

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Authors and contributors

 Andrea Rodrigo
Andrea Rodrigo
Embryologist
Bachelor's Degree in Biotechnology from the Polytechnic University of Valencia. Master's Degree in Biotechnology of Human Assisted Reproduction from the University of Valencia along with the Valencian Infertility Institute (IVI). Postgraduate course in Medical Genetics. More information about Andrea Rodrigo

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