IUI vs natural conception: what happens to the sperm in each

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This video is in Hindi; the guide on this page is in English.

Many couples ask what an IUI really adds, if the husband's sperm reach the womb anyway during intercourse. In this short video, in Hindi, our consultant answers that question with a model of the womb, the fallopian tubes, the ovaries and the vagina, cut open to show what happens inside. This guide explains the same difference in English.

Pai Hospital is registered as a Level 2 ART clinic under the Assisted Reproductive Technology (Regulation) Act, 2021 (Reg. No. GA/AC/2022/12689/L2/South Goa/02, valid to 14 January 2030).

What happens to the sperm after intercourse

During intercourse, the semen is deposited in the vagina, not inside the womb. The vagina is the entrance to the body, and it is naturally acidic, which protects a woman from bacteria and other infections. In the video, our consultant explains that this same acidity treats sperm much like any other visitor from outside, and many of them do not survive it.

That is why nature provides so many. In the video, our consultant gives a simple example: if a husband's count is 30 million sperm in each millilitre and the sample is about three millilitres, some 90 million sperm start the journey, and even if more than half are lost, tens of millions can still go on.

The sperm that survive must then swim through the cervix (the neck of the womb), up through the womb and into the fallopian tubes, where the egg is met and fertilised. That is a long way for a cell so small, and only a small share of the sperm get there. Timing matters too: the egg lives for only about a day after ovulation, so intercourse in the fertile window gives the sperm the chance to be waiting when the egg arrives.

What happens in an IUI

IUI stands for intrauterine insemination. Instead of leaving the sperm in the vagina, the sample is prepared in the laboratory first and then placed inside the womb:

1. The husband gives a semen sample on the day of the IUI.
2. The sample is washed and prepared: the seminal fluid is removed, and the most active, normally moving sperm are separated and concentrated. Read about sperm preparation for IUI.
3. Around the time of ovulation, the prepared sperm are placed high inside the womb through a thin, soft tube passed gently through the cervix.

In the video, our consultant shows on the model where the sample is placed, inside the womb and close to the openings of the tubes, and explains what IUI changes.

How IUI helps sperm reach the egg

• It avoids the acidic vagina. The sperm are placed beyond it, so they are not lost there.
• It shortens the journey. The sperm start inside the womb, a much shorter distance from the tube where fertilisation happens, in surroundings that suit them.
• Only the active sperm are used. Sperm that move poorly are left out during the preparation, so the sample placed is made up of sperm with good movement.
• The timing is planned. Follicle scans, and often a trigger injection, place the IUI close to ovulation.

What IUI does not change: the egg and the sperm still have to meet inside a fallopian tube, and fertilisation still happens there, as it does naturally. That is why IUI needs at least one open tube, and why IUI is a help to natural conception rather than a replacement for it.

IUI vs timed intercourse: when is IUI advised?

For many couples, the first step is simply timed intercourse in the fertile window, sometimes with tablets to help ovulation. IUI is usually considered when:

• the husband's sperm count or movement is mildly low;
• there is difficulty with intercourse, or the husband works away and his own sample is frozen in advance;
• the cervix may be stopping the sperm getting through;
• the cause of infertility is still unexplained after the basic tests;
• several months of timed intercourse, with or without ovulation tablets, have not worked.

IUI is not right for every couple. In the video, our consultant explains that when the sperm count is well below the level needed for IUI, ICSI, a form of IVF in which a single sperm is injected into each egg, is the route he would rather suggest. The count at which IUI is still reasonable is explained in the minimum sperm count for IUI, and the wider comparison in IUI vs IVF.

About this guide

This guide is by the Pai Hospital Team. Pai Hospital is at Vaddem, Vasco-da-Gama, Goa, with its own IVF laboratory, where the sample for an IUI is prepared. Consultations are held in Panjim, Margao, Mapusa and Vasco; the scans and the IUI are done at the hospital at Vaddem, Vasco-da-Gama.

This article is for education only and is not personal medical advice; please speak to your own doctor about your situation.

Your questions

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This page is for general education and is not personal medical advice. Treatment depends on your own examination and reports, so please speak to a doctor about your situation. We do not carry out or offer sex determination of any kind.