In vitro fertilization success rate
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While the overall live birth rate via IVF in the U.S. is about 27% per cycle (33% pregnancy rate), the chances of a successful pregnancy via IVF vary widely based on the age of the woman (or, more precisely, on the age of the eggs involved).  Where the woman's own eggs are used as opposed to those of a donor, for women under 35, the pregnancy rate is commonly approximately 43% per cycle (36.5% live birth), while for women over 40, the rate falls drastically - to only 4% for women over 42.  Other factors that determine success rates include the quality of the eggs and sperm, the duration of the infertility, the health of the uterus, and the medical expertise. It is a common practice for IVF programmes to boost the pregnancy rate by placing multiple embryos during embryo transfer. A flip side of this practice is a higher risk of multiple pregnancy, itself associated with obstetric complications.
IVF programmes generally publish their pregnancy rates. However, comparisons between clinics are difficult as many variables determine outcome. Furthermore, these statistics depend strongly on the type of patients selected.
There are many reasons why pregnancy may not occur following IVF and embryo transfer, including
- The timing of ovulation may be misjudged, or ovulation may not be able to be predicted or may not occur
- Attempts to obtain eggs that develop during the monitored cycle may be unsuccessful
- The eggs obtained may be abnormal or may have been damaged during the retrieval process
- A semen specimen may not be able to be provided
- Fertilization of eggs to form embryos may not occur
- Cleavage or cell division of the fertilised eggs may not take place
- The embryo may not develop normally
- Implantation may not occur
- Equipment failure, infection and/or human error or other unforeseen and uncontrollable factors, which may result in the loss of or damage to the eggs, the semen sample and/or the embryos
According to a 2005 Swedish study published in the Oxford Journal 'Human Reproduction' 166 women were monitored starting one month before their IVF cycles and the results showed no significant correlation between psychological stress and their IVF outcomes. The study concluded with the recommendation to clinics that it might be possible to reduce the stress experienced by IVF patients during the treatment procedure by informing them of those findings. While psychological stress experienced during a cycle might not influence an IVF outcome, it is possible that the experience of IVF can result in stress that leads to depression. The financial consequences alone of IVF can influence anxiety and become overwhelming. However, for many couples, the alternative is infertility, and the experience of infertility itself can also cause extreme stress and depression.
The major complication of IVF is the risk of multiple births. This is directly related to the practice of transferring multiple embryos at embryo transfer. Multiple births are related to increased risk of pregnancy loss, obstetrical complications, prematurity, and neonatal morbidity with the potential for long term damage. Strict limits on the number of embryos that may be transferred have been enacted in some countries (e.g., England) to reduce the risk of high-order multiples (triplets or more), but are not universally followed or accepted. Spontaneous splitting of embryos in the womb after transfer can occur, but this is rare and would lead to identical twins. Recent evidence suggest that singleton offspring after IVF is at higher risk for lower birth weight for unknown reasons.
Another risk of ovarian stimulation is the development of ovarian hyperstimulation syndrome.
If the underlying infertility is related to abnormalities in spermatogenesis, it is plausible, but too early to examine that male offspring is at higher risk for sperm abnormalities.
The issue of birth defects remains a controversial topic in IVF. A majority of studies do not show a significant increase after use of IVF. Some studies suggest higher rates for ICSI , while others do not support this finding. Major birth defect include chromosomal abnormalities, genetic imprinting defects, and multiple organ abnormalities. Hansen et al conducted a systematic review of published studies (including ICSI) and found a 30-40% increase risk of birth defects associated with assisted reproductive technology when compared to children born after spontaneous conception. Possible explanations offered were the underlying cause of the infertility, factors associated with IVF/ICSI, culture conditions, and medications, however, the actual cause is not known.
- Abington Reproductive Medicine, In Vitro Fertilization (IVF): Why Pregnancy May Not Occur. (2006)
- Kurinczuk JJ (2003). "Safety issues in assisted reproduction technology. From theory to reality--just what are the data telling us about ICSI offspring health and future fertility and should we be concerned?". Hum Reprod. 18 (5): 925–31. PMID 12721163.
- Hansen M, Bower C, Milne E, de Klerk N, Kurinczuk JJ (2005). "Assisted reproductive technologies and the risk of birth defects--a systematic review". Hum Reprod. 20 (2): 328–38. PMID 15567881.