For the male

Sperm quality, inflammation (e.g. prostatitis, orchitis), genital injuries, congenital abnormalities (e.g. hypospadias), other pathological conditions (e.g. varicocele), or exposure at work in high temperature environments, may affect sperm quality. However, a large percentage (20%) of male infertility etiology remains unknown.

For the female

Tubal abnormalities
The major cause of female infertility can be attributed to the fallopian tubes, the path through which the fertilized egg will travel to the uterus. A woman may not have fallopian tubes (e.g. surgical removal due to previous ectopic pregnancy) or may have blocked fallopian tubes (e.g. due to inflammation).

Abnormalities of ovulation
A woman may experience irregular ovulation or absence of ovulation (anovulation). In many cases, polycystic ovary syndrome is associated with ovulatory dysfunction, but this is not always the case. 20-30% of women presenting with polycystic ovaries do not encounter problems with their ovulation. Women with polycystic ovary syndrome may present with a wide range of features, ranging from those having a regular menstrual cycle to those presenting with obesity, amenorrhea and hormonal abnormalities.

Endometriosis
Endometriosis is a condition in which the endometrium -the mucous membrane that lines the inside of the uterus and is discharged with blood in every menstrual cycle- grows outside the uterus. Among women with endometriosis up to 50% may encounter infertility problems and 30-50% of infertile women may have endometriosis.

Age

Women over 40, loose rapidly their ability to conceive because their ovaries produce oocytes of lower number and quality, with a high incidence of chromosomal abnormalities (e.g. a 35 year-old woman has 1 in 300 chances of having a baby with Down syndrome when a 45 year-old has 1 in 30).

Thus, recent studies of  Preimplantation Genetic Screening (PGS) in women over 40 showed that 60-90% of embryos had chromosomal abnormalities – explaining the cause of their inability to conceive.

Uterine anatomical abnormalities may contribute to a couple’s infertility problems.

Unexplained infertility

When a couple can’t conceive, even though the female reproductive system and hormone profile are normal and the partner’s sperm parameters are also normal, then specialists refer to these cases as unexplained infertility (unknown cause).