In Intrauterine Insemination (IUI), with follicular studies showing an egg size of 19x18 mm on the 12th day, when should IUI be performed and will natural ovulation automatically trigger?

From the Guidelines

In an IUI cycle with a follicle measuring 19×18mm on day 12, I recommend triggering ovulation with an hCG injection rather than waiting for natural ovulation. The IUI should then be performed approximately 36 hours after the trigger injection, as this timing has been shown to not compromise pregnancy rates 1. While natural rupture could occur spontaneously with a follicle of this size, timing becomes unpredictable, which may result in suboptimal synchronization between ovulation and the insemination. The hCG trigger mimics the natural LH surge and provides more precise timing control. After the trigger, the mature egg is typically released within 24-48 hours. This controlled approach maximizes the chances of having viable sperm present when the egg is released. Some key points to consider in this decision include:

• The size of the follicle, which is already at a mature size of 19×18mm, making it a good candidate for triggering ovulation 1
• The use of hCG injection to trigger ovulation, which is a common practice in IUI cycles, especially when using gonadotrophins 1
• The timing of IUI after the trigger injection, which can be performed anywhere between 24 and 40 hours after the injection without compromising pregnancy rates 1 If you prefer a natural cycle without trigger, daily monitoring with ultrasound and LH testing would be necessary to detect the natural LH surge, with IUI performed 1 day after the LH rise, as this is the recommended approach for natural cycles 1. However, this approach is less predictable and may require more monitoring visits.

From the Research

Follicular Size and IUI Timing

• The size of the follicle is an important factor in determining the timing of intrauterine insemination (IUI) 2.
• A follicular size of 19-20 mm is associated with higher pregnancy rates in gonadotropin-stimulated IUI cycles 2.
• In the given scenario, the follicular size is 19x18 mm on the 12th day, which is within the optimal range for IUI.

Natural Ovulation and IUI

• Spontaneous triggering of ovulation by detecting LH rise is associated with higher ongoing pregnancy rates compared to administration of human chorionic gonadotropin (HCG) in patients undergoing IUI 3.
• The use of LH for timing ovulation in natural cycles might be the best way to maximize the probability of pregnancy for patients undergoing IUI 3.
• However, it is unclear whether natural rupture will automatically trigger ovulation, and the timing of IUI may still be important.

Timing of IUI

• The optimal timing of IUI after ovulation triggering is still a matter of debate 4, 5.
• Some studies suggest that IUI performed 24 hours after ovulation triggering may be associated with higher pregnancy rates in certain patient populations 5.
• However, other studies have found no significant difference in pregnancy rates with different timing intervals 4.