What is measured in IUI
There are a lot of numbers and levels that your fertility clinic might be tracking which can get confusing. What your fertility clinic is tracking, what they mean, and why they matter.
Hormones Commonly Tested During an IUI Cycle
1. Estradiol (E2)
What it is: A form of estrogen produced by growing follicles in the ovaries
Why it matters: Helps monitor follicle development and predict ovulation
Typical range before ovulation:
~150–200 pg/mL per mature follicle
Low levels early in the cycle, rising as follicles grow
2. Luteinizing Hormone (LH)
What it is: The hormone that rises right before ovulation
Why it matters:
A surge in LH signals your body is about to ovulate
IUI is usually scheduled 24–36 hours after this surge (or triggered with a shot)
Surge level: Often >15–20 mIU/mL, but this can vary
3. Follicle-Stimulating Hormone (FSH)
What it is: A hormone that stimulates the ovaries to develop follicles
Why it matters: Often tested on Cycle Day 2–4 to assess ovarian reserve and baseline function
Typical range (CD2–4):
~3–10 mIU/mL
Higher levels may suggest reduced ovarian reserve
4. Progesterone (P4)
What it is: The hormone that supports the uterine lining after ovulation
Why it matters:
Confirms ovulation occurred
Supports early pregnancy
Typical range (7 days post-ovulation):
≥3 ng/mL confirms ovulation. Helpful to check if someone is unsure if they are ovulating.
However, there is not a target progesterone level after IUI; measuring progesterone levels is unreliable and is not clinically proven to help in IUI cycles.
5. Anti-Müllerian Hormone (AMH) (pre-cycle)
What it is: A hormone produced by early immature follicles; reflects ovarian reserve
Why it matters:
Doesn’t correlate with IUI success
Used to determine IVF-specific prognosis
Higher AMH = higher ovarian reserve -> more eggs likely to be stimulated
Low AMH = lower ovarian reserve -> less eggs likely to be stimulated
Typical range: >1.0 ng/mL
Additional Hormones (Less Common, but Sometimes Checked)
6. Thyroid Stimulating Hormone (TSH)
Why it matters: Thyroid health is key for fertility and early pregnancy
Target range for fertility: <4 μIU/mL
7. Prolactin
Why it matters: High levels can interfere with ovulation
Normal range: ~5–25 ng/mL (but labs vary)
8. Androgens (Testosterone, DHEA-S): Sometimes checked in cases of PCOS or ovulatory issues
During an IUI cycle, monitoring follicle growth is key to timing the insemination correctly and maximizing the chances of pregnancy. Here’s what your doctor is typically looking for when they track follicles via transvaginal ultrasound:
Follicle Size: What’s Considered “Mature”
Mature follicle = 18–24 mm
This is the target size range for ovulation. Once a follicle (or follicles) reach this size, the provider may schedule the IUI and/or instruct you to administer a trigger shot (usually hCG) to induce ovulation.
Too small (<14 mm): Unlikely to contain a viable egg
Too large (>24 mm): May indicate a post-mature egg or risk of cysts
Ideal Follicle Size Timeline (For Medicated IUI Cycles)
| Cycle Day | What's Happening | Typical Follicle Size |
|---|---|---|
| CD 2-4 | Baseline ultrasound/td> | <10 mm (resting follicles) |
| CD 8-12 | Monitoring visits begin | 12-16mm (growing) |
| CD 12-14 | Trigger or ovulation expected | 18-24 (mature) |
What’s the ‘right’ number of follicles
1 mature follicle is ideal for:
Natural cycle IUI or for those with ovulatory issues
2–3 follicles may be acceptable depending on age, history, and comfort with twin/multiple risk
Usually seen in patients taking oral or injectiable medications
4+ follicles ≥14 mm:
Many providers may cancel the cycle to avoid a high-risk multiple pregnancy depending on age and history
Hormone Levels That Accompany Follicle Growth
Ultrasounds are often paired with bloodwork:
Estradiol (E2):
Rough guideline: ~150–200 pg/mL per mature follicle
Helps assess follicle function and estrogen response
LH (Luteinizing Hormone):
A surge indicates your body is trying to ovulate naturally
If a surge is detected, IUI will be scheduled the next day usually
Progesterone: A steroid hormone whose main job is to prepare and maintain the uterine lining (endometrium) so that a fertilized egg can implant and grow.
Can be checked post-IUI to confirm ovulation occurred
| Measurement | Target Range |
|---|---|
| Follicle size (mature) | 18-24 mm |
| Number of mature follicles | 1-3 |
| Estradiol (E2) per follicle | ~150-200 pg/mL |
| LH | Surge = ovulation soon |
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