Intrauterine insemination (IUI) is a technique of assisted conception in which washed and sorted motile sperm is inserted through the uterine cervix into the uterine cavity to increase the chances of natural fertilization of the oocyte within the fallopian tubes. It is indicated in severe or moderate male factor infertility and in mild unexplained infertility.
Its chances of success depend upon several factors. The live birth rate is lower than the pregnancy rate, and therefore the success rates published by various centers should be evaluated accordingly.
1. Cause of infertility
First of all, conception rates depend, though marginally, on the reasons for infertility. The duration of infertility also plays a role. Infertility due to anovulation or unexplained infertility is somewhat more easily treated with IUI than is endometriosis or male factor infertility.
2. Ovarian hyper stimulation
Whether or not medications are used to induce ovulation and the type of protocol used may have an effect on the success rates. The follicular response and increase in endometrial thickness following induction of ovulation may also act as prognostic markers, though not statistically significant. Many centers have reduced the dosage of drugs used to stimulate the ovaries because of the high risk of multiple pregnancies with these protocols. Superovulation does double or triple the pregnancy rates but also the number of multiple pregnancies. This can be as high as 20 percent for twins, and 40 percent for higher-order gestations. Ovarian hyperstimulation syndrome is also a foreseeable risk with increasing numbers of preovulatory follicles.
The age of the woman undergoing the procedure significantly affects how well it works. Women who are below the age of 40 years, in general, have a more than 50 percent chance of achieving pregnancy after six cycles of IUI, with a success rate of over 75 percent after 12 cycles. Some other sources put the cumulative pregnancy rate at 20-33 percent with six cycles of ovarian hyperstimulation with IUI.
The importance of female age lies in the well-established reduction in oocyte quality as age increases, which is not offset by overcoming barriers to fertilization. IUI success rates start to decline even after the age of 35 years. For women above 40 years, live births may occur in only about 1.5 percent of women who have undergone IUI treatment cycles. For these reasons, this is a poor option for women older than 40 years, and even after the age of 35 it should be offered with extreme caution.
4. Semen parameters
Sperm count and sperm preparation techniques may make a difference in the ease of conception with IUI.
The use of fresh sperm has a higher conception rate than the use of frozen and thawed sperm. The sperm characteristics affect pregnancy rates, including the total motile fraction (TMF), the morphology and the motility of the washed sperms. The TMF significantly increases the pregnancy rate to almost double, when it is between 10 and 20 million, but its reduction to less than 10 million is associated with low success rates, and also a count above 20 million, though the reason for this latter finding is unknown. Even within this classification, a TMF of less than 1 million was linked to disappointing rates, while a TMF less than 5 million depends for its success mostly on the sperm morphology, ranging from less than 6 percent when abnormal sperms are abundant to almost 20 percent when normal morphology is present in most sperms.
5. Timing and number of inseminations
If the timing of ovulation is not correctly detected, the time of insemination may not be synchronized with the period of peak female fertility within the cycle. Thus the appropriate technique for working out whether ovulation has occurred or not needs to be used. A premature LH surge occurs in many cases, from a quarter to a third of treated women, which reduces the pregnancy rates. The use of LH antagonists or the use of clomiphene citrate to prevent an early surge is under study and may produce a significant rise in the success rates.
Number of inseminations within a cycle: If insemination is repeated twice within the same cycle, the number of pregnancies may go up.
6. Donor sperm
Successful insemination with donor sperm is again linked with the age of the woman, and has a 22 percent conception rate per cycle compared to less than 10 percent when only homologous sperm is used. Its use resulted in the following per cycle live birth rates:
- Under 35 years - about 16 percent
- 35 to 39 years - 11 percent
- 40 to 42 years - less than 5 percent
- 43 to 44 years - just over 1 percent
- Over 44 years - nil
However, higher rates have been reported in the US, with 10-15 percent live births in the 41-42 year age group, and 5 percent in women older than 42 years.
It is important to establish robust prognostic factors which can help to formulate guidelines to make IUI more focused in its application. This will increase the live birth rates and reduce the number of unhelpful IUIs performed. For instance, couples with male factor predominating as a cause of infertility, female age above 40 years, and with a TMF below 5 million, would be ideal for in vitro fertilization rather than IUI. Considering the low pregnancy rates per cycle, many couples might prefer to attempt another more effective procedure once than undergo the emotional, physical, and financial strain of repeated IUI cycles, especially when they live in remote locations.
Reviewed by Susha Cheriyedath, MSc