Intrauterine insemination (IUI), sometimes referred to as “artificial insemination,” is the process of placing sperm in a woman’s uterus. This procedure delivers sperm past the vagina and cervix, both harsh environments for sperm, and into the uterus near the fallopian tubes, thereby raising the chances sperm will fertilize a woman’s egg.
IUI is often (but not always) supplemented with medications that can help induce ovulation or grow multiple eggs, namely letrozole, clomid, or gonadotropins.
IUI is able to enhance results for specific patient types, but does little address those with poor egg supply (Diminished Ovarian Reserve), severely reduced sperm count (oligospermia or azoospermia), or an unfriendly uterine environment (where a pregnancy needs to take place).
In the continuum of fertility care, IUI represents a “middle ground,” being more successful and costly than simply taking medication, while being inferior to and cheaper than IVF.
The worrisome health risk associated with IUI is that 8 - 30% of pregnancies result in twins or triplets. This “multiples risk” is more easily controlled in IVF. The reason twins and triplets are problematic is that they increase the risks to both mother and offspring, as shown below.
However, because the odds of pregnancy are relatively low with IUI, the odds any given IUI cycle leads to a multiple birth are low on an absolute basis, roughly 0.5% - 2.5%.
Below is data from over 17,000 IUI cycles which demonstrates how IUI success rates decline with age. You’ll note that this phenomenon also applies to IVF, which still drastically outperforms IUI at every age interval.
Similarly, success rates also very much depend on which drugs a woman takes in accompanying her IUI cycle. Below are data amalgamated from two superb studies on couples with unexplained infertility that elucidates the point.