IUI puts prepared sperm into the uterus and lets fertilization happen naturally; IVF moves fertilization into the lab and transfers an embryo.
That single difference drives all the others. IUI is a minutes-long catheter procedure timed to ovulation, with mild or no stimulation drugs and a modest price tag. IVF means injectable stimulation, monitoring, a sedated egg retrieval, laboratory fertilization, embryo culture, and transfer, at roughly ten times the cost per cycle. IVF also wins per-attempt on success rates, sometimes several-fold. So the standard logic: IUI first when the problem is unexplained, mild, or donor-sperm-related, because it is cheaper and gentler; IVF first (or soon) when tubes are blocked, sperm counts are severely low, egg reserve is diminished, age is a factor, or IUI has failed a few times. Neither is a character test: they are rungs on a ladder, and many people use both in sequence.
What to do
Common questions
What is the difference between IUI and IVF?
The core difference is where fertilization happens. In IUI (intrauterine insemination), specially prepared, concentrated sperm is placed directly into the uterus with a thin catheter around ovulation, but the sperm still has to reach and fertilize the egg inside your body on its own. In IVF, eggs are removed, fertilized in a lab, grown for several days, and an embryo is placed in the uterus, so IVF handles fertilization for you. Everything else follows from that. IUI is quick (the insemination takes minutes, feels like a Pap smear, no anesthesia), uses little or no medication or a mild course, and costs a fraction of an IVF cycle. IVF is a weeks-long process of injections, monitoring, a retrieval procedure, lab work, and transfer, costing roughly ten times more. Success per attempt is the trade: IVF's per-cycle success is substantially higher than IUI's, which is why IUI is usually tried first for unexplained infertility, mild male-factor issues, or donor-sperm conception, and IVF is the route for blocked fallopian tubes, severe male factor, low egg reserve, older age, or after several failed IUI cycles. A common clinical path is 3 to 4 IUI attempts, then IVF if they do not work.