Factors Affecting Success of Infertility Treatment

Not every ART cycle will result in a baby, due to many biological and patient factors as listed below.

Biological factors:

  • Inadequate response to ovarian stimulation treatment resulting in a cancelled egg retrieval.
  • Not every “follicle” contains an egg – some may be cysts.
  • Ovulation may occur before the eggs can be harvested. Once this happens recovering an egg is almost impossible.
  • Egg quality and egg maturity will affect fertilization rates and subsequent embryo development.
  • Even with mature eggs fertilization rates are around 60-70%. No fertilization is fortunately rare these days with ICSI but may happen if there are only 1 or2 eggs available.
  • On average 4 -5 blastocysts will develop from 10 fertilized eggs. Most commonly the ones that fail to develop to blastocysts do so mainly because of an imbalance in the number of chromosomes contributed by the sperm or egg. It may also occur because the embryos own DNA fails to activate properly to control development.
  • Not all blastocysts will be of sufficient quality to transfer or freeze.

Patient factors

  • The most significant factor is female age.
    • The natural monthly conception rate is around 16% in women aged 30 and falls to 5% in women aged 40.
    • Older women tend to produce fewer eggs in response to ovarian stimulation.
    • Older eggs tend to have higher levels of chromosomal imbalances and other functional problems.
    • Foetal chromosomal abnormalities increases from 1 in 385 in women aged 30 to 1 in 63 for women aged 40.
    • Miscarriage rates increase from less than 10% in younger women (early 20’s) to 50% in women 42 or more.
  • Older men may have higher levels of damage to DNA in their sperm affecting embryo development.
  • In men over 45 years of age conception can take up to 5 times longer compared to men in their 20’s
  • Obesity in both men and women can affect fertility due to hormonal changes.
  • Miscarriage and other pregnancy related risks are higher in obese women. Babies born to obese women are at higher risk of adverse outcomes compared to those born to mothers in the normal weight range.
  • Other factors affecting sperm and egg quality are; caffeine, alcohol, smoking
  • The specific cause of infertility may have an impact.

The Fertility Society of Australia and Access Australia have more information regarding life style factors and interpreting pregnancy rates. A link to national results is provided below: