Updated by the Progyny Clinical Team — June 2025.
What is intrauterine insemination (IUI)?
IUI is a type of fertility treatment. It helps sperm get closer to the egg during ovulation, which may improve the chances of pregnancy.
Many IUI cycles use medications to help the body grow eggs and time ovulation. If you don’t ovulate regularly, your fertility provider may call this “ovulation induction.” If you do ovulate regularly, it’s called “ovarian stimulation.” In both cases, your provider will monitor you closely to see how your body is responding.
Your fertility team wants to give you the best chance of success while keeping you safe. It’s important to understand the risks of treatment, and why your IUI cycle may need to be canceled in some cases.
How do these medications work?
Your provider may give you either pills or injections to help your ovaries grow one or more eggs. These medications are used in both ovulation induction and ovarian stimulation.
Oral medications (pills):
- Clomid (clomiphene citrate): This medicine tricks the brain into thinking your estrogen levels are low. That causes the brain to make more FSH (follicle-stimulating hormone), which helps the ovaries grow eggs.
- Letrozole: This pill lowers the amount of estrogen that your body produces. Like Clomid, it leads to more FSH being released, which helps eggs grow.
Injectable medications:
- Gonadotropins (like Gonal-F, Follistim, or Menopur): These are the same hormones your body makes naturally to grow eggs (FSH and LH), but in higher amounts.
They’re often used for in vitro fertilization (IVF), but sometimes in IUI cycles at lower doses.
What happens during an IUI cycle?
- Cycle starts: You’ll come in for blood work to make sure your hormone levels are at their normal starting point.
- Medications begin: You’ll take either pills (Clomid or Letrozole for five days) or injections. Pills are usually followed by an ultrasound a few days later to check for growing follicles. Injections are monitored more closely, with visits every one to three days.
- Follicle growth: Each follicle holds one egg. As follicles grow, they make estrogen. Blood work and ultrasounds help your provider know when the follicles are mature (usually when they reach about 18mm).
- Triggering ovulation: Once your follicles are ready, you may take a shot of human chorionic gonadotropin to cause ovulation in about 36 hours. Your IUI will be scheduled about 24–36 hours after this shot. In some cases, ovulation may happen naturally and be tracked with ovulation predictor kits or blood work.
- Sperm sample: On the day of the IUI, a fresh or frozen sperm sample (from a partner or donor) is prepared in the lab. The lab “washes” the sample to keep only the best-moving sperm.
- The procedure: A small tube is inserted through the cervix and into the uterus to place the sperm close to the egg. The process is quick and usually painless. You can go back to normal activities afterward.
IUI success rates vary, but are usually around 15 to 20% per cycle, depending on your age and diagnosis.
What are the risks of IUI with medication?
The main risk is multiple pregnancy, meaning twins or more, if more than one follicle grows. While more follicles can increase your chances of getting pregnant, they also raise the chance of carrying twins or higher-order multiples, which have more risks for both the pregnant person and the babies.
Risk by medication type:
- Letrozole: Used for people who don’t ovulate regularly. Lowest risk of multiple follicles and multiple pregnancy (2–4%).
- Clomid: Often used for unexplained infertility. Slightly higher risk of multiple pregnancy (about 8%).
- Gonadotropins: Highest chance of multiple follicles and multiple pregnancy — more than 20%. Rarely used for IUI because of this risk.
Triplets or more happen in about 2% of IUI cycles, depending on your age and how many follicles you grow.
Studies show that once more than two to three follicles grow, your chance of having a healthy single pregnancy doesn’t go up much, but your risk of a multiple pregnancy goes up a lot. That’s why your provider may recommend canceling your IUI cycle if too many follicles grow.
Why are multiple pregnancies risky?
Carrying twins, triplets, or more increases the risk of problems for both you and your babies.
Risks for the pregnant person:
- High blood pressure
- Gestational diabetes
- C-section delivery
- Heavy bleeding after birth
Risks for the babies:
- Miscarriage or stillbirth
- Premature birth
- Low birth weight
- Breathing problems
- Long-term health or brain development issues
The more babies there are, the higher the risk. Some patients who become pregnant with triplets or more may choose a procedure called selective reduction (for example, reducing triplets to twins). This can lower the chance of serious complications, but it comes with risks and is a deeply personal decision. Your fertility team can support you through this process.
When should an IUI cycle be cancelled?
If you grow more than three follicles, your provider will talk to you about the risk of multiples. If the risk is too high, your IUI cycle may be canceled. If that happens, you should avoid intercourse during your fertile window to lower the chance of getting pregnant with multiples. You’ll try again in your next cycle, possibly with a lower medication dose.
Some people choose to move on to IVF instead. IVF lets you grow multiple eggs, make embryos, and then choose the healthiest one to transfer. It’s a safer way to try for one baby, as only a single embryo is placed in the uterus. While one embryo can still split into identical twins, the overall risk of multiples is much lower than with IUI.
All in all
Your fertility team wants to help you get pregnant in the safest way possible. Sometimes that means canceling a cycle to avoid risks. While this can be disappointing, it’s done with your health in mind.
Talk openly with your provider about your treatment plan, risks, and all your options. They’re there to help you make the best decisions for your unique situation.
If you have questions or concerns, Progyny is here for you. Please contact your Progyny Care Advocate for support.
Disclaimer: The information provided by Progyny is for educational purposes only and is not medical advice. Always consult a qualified healthcare provider for medical guidance.