Several things can happen to cause infertility. This can happen with the female, male, or both partners. Or, it can be several things happening to either, or both partners at one go.
When it is multiple causes with both partners, a scenario like this may play out; The woman has endometriosis and has poor egg quality, possibly from being older, like the later 30’s or more and the man has a low sperm count and abnormally formed sperm. This is a highly problematic scenario. Any combination scenarios may play out, either like the example given or different in other ways from this example.
Womb structure problems and other related things, such as endometriosis can be part, or most of a cause of infertility. Quality of eggs and ovulation problems can be another one of the causes of infertility. Symptoms related to this can range from absent periods up to overly heavy periods, or irregular periods.
Polycystic Ovary syndrome can be a cause, too. Polycystic ovaries are where there are cysts all over the ovaries that interfere with ovulation and these people may not ovulate regularly. Blocked or damaged tubes can be more common causes of infertility.
Causes of infertility for men are different as it is a different system that we will be dealing with here. There can be blockages in the male tubes that carry sperm around the male tract. Sperm problems can be that there is a low sperm count and they can be abnormally shaped or the sperm has poor motility. Men and women can both have a sperm allergy.
In either partner, a genetic translocation can happen where any of the five acrocentric chromosome pairs like the 13,14,15,21 and 22 have a translocation called a Robertsonian translocation.
Kallmann Syndrome is a form of hypogonadism where the hypothalamus does not produce the sex hormones needed to make the sex glands function. The symptom of this can be the inability to smell or a decreased ability to smell.
Environmental toxins can reduce fertility too. Things like work related exposure to glues and solvents can have this effect. Pesticides and silicones can have this happen too, most likely even in women, too. Try to stay away from unnecessary chemicals and so on when you are trying to become pregnant.
Adeno-associated virus might have a role in male infertility. This virus may alter the DNA of humans adversely can cause infertility. This prevents tainted DNA from being passed on. Otherwise, this virus is harmless.