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Factors affecting IVF success rate


Overall success rate in the treatment clinic

The HFEA 2002 report has demonstrated that in the UK, the overall live birth rates per IVF treatment cycle was 22% and varies between different clinics. It ranged from anywhere between 10% to 46%.

What are the possible causes for the difference in IVF success rates?

The size of the clinic

In general, large IVF centres have higher success rates than small clinics. However, some small clinics have very good results.

Live birth rate per treatment cycle

Information source HFEA 1997 Report SART 2002 Report
Large centres 15.7% 34.3%
Small centres 12.6% 30.0%

Skill and experience of the team including, doctors, nurses and embryologists

Even in the same clinic with the same clinical protocol and a single embryology laboratory, IVF outcome varies between different doctors. Karandi et al 1999 (Fertility & Sterility Journal) reported that the clinical pregnancy rates vary between 8.3 to 40% between different physicians. Similarly IVF outcome varies between different embryologists (source Fertility & Sterility Journal 1999).

The technique of embryo transfer

Variations in embryo transfer techniques can affect the result of the treatment.

The type of ovarian stimulation protocol

Natural cycle or clomiphene stimulated IVF have poor success rates per treatment cycle compared  to Gonadotropin-releasing hormone (GnRh) agonists and gonadotropins.

GnRh agonists in addition to gonadotropins for ovarian stimulation result in higher pregnancy and live birth rates than using gonadotropins alone.

There is a small but significant increase in pregnancy rates following the use of high purity gonadotropins or recombinant FSH compared to hMG.

Quality of cycle monitoring

Assisted hatching and blastocyst transfer

There is some evidence that assisted hatching in selected groups of patients, result in improvement of pregnancy and live birth rates. Similarly, there is evidence that blastocyst transfer result in improvement in pregnancy and live birth rates with lower incidence of multiple pregnancy rates because of transfer of less number of embryos.

Age group less than 35 35-37 38-40 41-42 43 or over
Blastocyst transfer 44.3% 37.6% 29.4% 18% 7.5%
Cleaved embryo transfer 37.6% 32.7% 24.4% 14.3% 5.7%

Live birth rate per treatment cycle using donated own eggs. Data adapted from SART report 2000

What are the factors that influence the outcome of IVF treatment?

The success of IVF treatment depends on several factors.

The chance of an individul couple of having a baby following one completed cycle of IVF treatment depends on two main factors. Firstly, the overall success rate of the treatment clinic (centre) and secondly, the characteristics of couple seeking treatment.

The overall live birth rate per treatment cycle is rising steadily by approximately 1% a year. Each age group has experienced significant increases in success rates.

Age 1996 1997 1998
Less than 35 28.4% 30.7% 32.2%
35-37 23.4% 25.4% 26.1%
38-40 16% 17% 17.9%
Over 40 6.4% 7.3% 8.3%

Data adapted from the SART report 2002

Age 1989-1999 1999-2000 2000-2001
Less than 38 22.1% 23.6% 25.1%
All ages 19.5% 20.7% 21.8%

Data adapted from the HFEA patient reports 2000 and 2002

In Vitro Fertilization

IVF pregnancy outcomes

As with all normally conceived pregnancies, complications may occur following IVF treatment. The table below summarizes the overall outcome of IVF pregnancies compared to natural conception.

  IVF pregnancy Natural conception Comments
Miscarriage 14-30% 15-20% Slight increase, due to older age.
Ectopic pregnancy 1-11% 0.2-1.4% Increase due to many factors.
Preterm delivery 24-30% 6-7% Four-fold increase.
Small birth weight 27-32% 5-7% Five-fold increase.
Stillbirth rate 1.2% 0.6% Two-fold increase.
Perinatal death 2.7% 1.0% Two-fold increase.
Congenital abnormalities 0.8-5.4% 0.8-4.5% No significant increase.
Caesarean section 33-58% 10-25% Increase mainly because of multiple pregnancy and woman's age.
Multiple pregnancy
twins 24-31% 1.2-4.5% Increase due to higher number of embryos transferred.
triplets 0.5-5.2% 0.012%
quadruplets 0.5% 0.0001%

Outcome of children born following IVF treatment

Follow-up of children born as a result of IVF, ICSI and other forms of assisted conception is needed to study issues such as genetic risk, congenital malformation, psychological development, educational development, fertility, and risk of cancer. Current data demonstrated no significant differences in the incidence of congenital and chromosomal abnormalities in children conceived after IVF compared to children conceived naturally. Furthermore, children appear to develop normally both from fresh and frozen embryo transfer.


Aids to Obstetrics and Gynaecology, Fourth edition (ed.) G. M. Stirrat. 1997

Beral V, Doyle P. MRC Working Party on Children Conceived by In Vitro Fertilization: births in Great Britain resulting from assisted conception. 1978-1987. BMJ 1990; 300

Bergh T, Ericson A, Hillensjo T, Nygren K-G, Wennerholm U-B. Delivery and children born after in-vitro fertilization in Sweden 1982-95. The Lancet 1999. 354

HFEA Report 2005. Human Fertilisation and Embryology Authority. United Kingdom

Rizk B. The outcome of assisted reproductive technology. In A textbook of In Vitro Fertilization and Assisted Reproduction, Second edition (ed.) P. R. Brinsden. 1999

SART Report 2000. Fertility & Sterility.

Characteristics of the couples seeking IVF treatment

There are many factors that may affect the outcome of IVF treatment. These may include one of the following characteristics of the couples seeking IVF treatment.

The age of the woman

The age of the woman has a significant affect on her fertility and the live birth rate decreases significantly from the age 35 years when the woman is using her own eggs. The older the woman, the higher the chance of cancellation, the lower the chance of success and the higher chance of miscarriage and chromosomal abnormalities. In the USA the live birth rate of women aged 41 and over was 7.1% per cycle initiated.

Live birth rates per IVF treatment cycle
Age group Less than 35 35-37 38-40 41-42 43 or over
Egg collection 90% 86% 81% 77% 73%
Embryo transfer 85% 81% 76% 71% 64%
Pregnancy 80% 32% 25% 16% 8%
Live birth 33% 27% 18% 10% 4%

Data adapted from SART report 2002

Womens age Cancellation rate
Less than 35 7.7-10%
35-37 11.6-14.7%
38-40 14.6-19.5%
Over 40 19.1-24.6%

Data adapted from SART report 2002

Use of donated eggs, donor embryos or donor sperm

The highest live birth rates are found among women who have had IVF with donated eggs, donor sperm or donated embryos.

Live birth rate per cycle in couples who have had IVF with their eggs and sperms compared with IVF using donor sperm, donated eggs and donated embryos. The overall delivery rate per transfer following the use of donor eggs was 41.2% compared to 31.1% following IVF using own eggs (data from SART report 2002).

Own eggs and sperm 15.4%
Own eggs and donor sperm 19.9%
Own sperm and donated eggs 21.9%
Donated eggs and donor sperm 22.2%

Data adapted from HFEA Report 1997

Number of embryos transferred

In general, the higher the number of embryos transferred, the greatest the chance of success. In the UK a maximum number of embryos to be transferred per treatment cycle is three. There is trend to transfer only two embryos especially in younger women to reduce the risk of multiple pregnancies.

Number of embryos replaced Live birth rate per cycle Multiple pregnancy rate
One 6.8% 4.7%
Two 16.8% 24.3%
Three 21.4% 32.6%

Data adapted from HFEA Report 1997

There is some evidence that the live birth rates for treatment where two embryos are transferred (provided that more than four embryos were created) is almost identical to the live birth rate for treatments where three embryos are transferred but with a lower multiple pregnancy rate.

Number of embryos replaced Live birth rate per cycle Multiple pregnancy rate
Two 26.4% 26.0%
Three 26.0% 34.3%

Data adapted from HFEA Report 1998

Women aged 40 years and older: Transfer of two embryos is recommended if using donated eggs. However if using their own eggs, then the transfer of three or four embryos (if allowed) is advised because both the chance of success and multiple pregnancy are lower when using own eggs compared to donated eggs.

Duration of infertility

The longer the couple has been infertile, the lower the chance of success.

Duration of infertility Live birth rate per embryo transfer cycle
1-3 years 19.5%
4-6 years 18.7%
7-9 years 17.0%
10-12 years 16.4%
Over 12 years 11.8%

Data adapted from HFEA Report 1999

Cause of infertility

Outcome of IVF treatment varies with the cause of infertility.

Cause of infertility Live birth rate per embryo transfer cycle
Tubal 13.3%
Endometriosis 15.0%
Unexplained 15.9%
Male 19.6%

Data adapted from HFEA Report 1997

Number of previous IVF treatment cycles

Live birth rates is highest in the first cycle (17.4%) and drop to 14.4% by the fifth cycle (HFEA Report 1999). Although cycles 6-8 appear to give a reasonable chance of success, few patients persevere that long.

Age group less than 35 35-37 38-40 41-42 43 or over
No previous treatments 33.9% 27.3% 18.7% 11.2% 3.8%
Had previous treatment cycles 28.5% 23.7% 16.1% 8.7% 3.7%

Data adapted from SART report 2002

Previous pregnancy and live birth

Woman, who has been pregnant before or has had a previous IVF birth, has a higher chance of success than woman who has never been pregnant.

The relation between previous pregnancy and live birth and the live birth rate per treatment cycle.

Previous pregnancy or live birth rate Live birth rate per embryo transfer cycle
Woman has never been pregnant 12.5%
Woman conceived naturally but no live birth 13.7%
Woman conceived naturally and has a live birth 15.3%
Woman conceived by IVF but no live birth 16.6%
Woman conceived by IVF and has a live birth 23.2%

Data adapted from HFEA Report 1998.

The presence of hydrosalpinges

There is increasing evidence that the presence of hydrosalpinges adversely affects the live birth rates of women undergoing IVF treatment. The mechanism for reduced implantation in women with hydrosalpinges is not fully understood but it is possible that the leakage of the fluid from the tube into the womb wash off the embryos, or the fluid itself could have toxic effects on the embryos.

Most specialists offer surgical treatment for hydrosalpinges before IVF treatment. The treatment usually inviolves removal of the tube (salpingectomy) preferably by laparoscope. An alternative is to occlude the tube at its uterine end again by laparoscopy or aspiration of the fluid from the tube.

A recent Cochrane Database Review has demonstrated the efficacy of laparoscopic salpingectomy in improving live birth rates in women with hydrosalpinges due to undergo IVF treatment. NICE Fertility Guidelines in the UK advocates that women with hydrosalpinges should be offered salpingectomy, preferably by laparoscopy, before IVF treatment.