Causes of Infertility - Female

Failure to ovulate is extremely common and effects almost 50% of women with fertility issues. Causes include:

• ovarian cysts or polycystic ovarian syndrome
• endometriosis within the ovary
• primary ovarian insufficiency (premature-early loss of oocyctes)
• endocrine disorders of the pituitary - poor production of:

                  - follicle stimulating hormone (FSH)

                  - luteinising hormone (LH)

                  - abnormal thyroid function

                  - excess prolactin. 

The female is born with a set number of oocytes (eggs) which undergo a process of atresia. 

Atresia is natural reduction of in a follicle's ability to develop and release an egg. The rate at which this happens varies. 

Fertility rates tend to reduce after the age of 35 and the remaining oocytes/eggs become more resistant to pituitary stimulation at this time.

Lifestyle factors effect fertility, such as:

• obesity is associated with PCOS / insulin resistance and can affect ovulation quality as well as implantation. 
• being underweight affects ovulation quality and cycle regulation. 
• excess training/physical exercise can impair ovulation-although moderate healthy amounts of exercise can boost fertility.
• Smoking, drinking and illicit drug use all affect ovulation, even after discontinuation as this may have impacted upon oocyte quality and development in the past.

After the embryo has formed by fertilisation of the egg in the fallopian tube, it must be transmitted along the fallopian tubes to implant in the uterine lining.

Blockage of the fallopian tubes prevents this and therefore implantation cannot occur.

Causes of fallopian tube blockage include:

• previous infections such as chlamydia, peritonitis or other ascending infections
• previous surgery such as ectopic pregnancy intervention
• endometriosis where tissue which normally lines the inside of the uterus, develops within the fallopian tube and other gynaecological or peritoneal structures, causing scarring and blockage.

Uterine structural abnormalities include: 

• Fibroids - these are firm growths that occur generally within the wall of the uterus, but can impact upon the endometrial cavity.
• Adenomyosis - an inflammatory condition which affects the wall of the uterus, but it can also affect implantation.
• Endometrial polyps - these are growths that are usually benign and occur on the lining of the uterus and either make it difficult for the embryo to implant or increase the risk of miscarriage if the embryo does implant.
• Scarring from previous surgery
• Malformations - such as bicornuate uterus (heart shaped uterus), septate uterus where a membrane separates the uterus into two parts.

This would be identified during the preliminary investigations.

Implantation occurs 3 to 5 days after ovulation, when the embryo arrives at the uterus. Implantation or attachment to the maternal circulation is required to maintain growth of the developing embryo.

Poor implantation can occur for many reasons-thin endometrium with poor blood supply, poor quality follicular development and low levels of oestrogen, endometriosis or adenomyosis, scarring in the endometrial cavity (possibly from previous surgery), poor quality or defective embryo.

This is a condition where the ovaries stop producing follicles and eggs much earlier than is usually expected. The remaining egg quality is poor and unresponsive to normal stimulatory hormones such as FSH (Follicle Stimulating Hormone) and LH (Luteinising Hormone). Sometimes, fertility stimulating treatments can encourage the remaining follicles to develop and IVF methods can also utilise remaining eggs to enable conception. 

Autoimmune conditions result in an abnormal immune response to normal body tissues. This can cause damage to organs, inflammation and difficulties with fertilisation and implantation. 

If implantation does occur, autoimmune diseases are often associated with increased risk of miscarriage due to rejection of the developing embryo.