FSH: Follicle Stimulating Hormone

FSH is produced by the pituitary gland in the brain.

Its role is to stimulate ovarian follicles and support egg maturation.

 

One way to think of FSH is as the brain’s message to the ovaries:

“Let’s recruit and grow follicles for this cycle.”

 

When ovarian reserve declines, the ovaries become less responsive. The pituitary gland may compensate by producing more FSH.

For this reason, elevated FSH levels may suggest reduced ovarian reserve.

 

Common Reference Ranges (Day 2–5)

• Below 10 IU/L: generally considered reassuring
• 10–15 IU/L: may suggest declining reserve
• 15–20 IU/L: often associated with significantly reduced reserve
• Above 25–30 IU/L: may indicate severely diminished reserve

These values should always be interpreted together with age and other markers.

For example, an FSH of 12 IU/L may carry very different implications in a 28-year-old woman than in a 41-year-old woman.

 

Important Limitation

FSH can fluctuate considerably between cycles.

Many fertility specialists consider the highest repeated value more informative than a single isolated result.

 

Estradiol (E2)

Estradiol is the primary estrogen produced by developing follicles.

It plays an important role in:

• Endometrial growth
• Follicle development
• Communication between the ovaries and the brain

Early Cycle Estradiol

Early follicular phase estradiol is usually relatively low.

Many laboratories consider values below approximately 50 pg/mL reassuring in the early follicular phase.

 

Why Estradiol Matters Together With FSH

Estradiol suppresses FSH through negative feedback.

If estradiol is elevated at the beginning of the cycle, FSH may appear artificially lower than expected.

This means a seemingly normal FSH result can occasionally mask a reduced ovarian reserve.

For this reason, fertility specialists usually interpret FSH and estradiol together rather than separately.

 

LH: Luteinizing Hormone

LH is another hormone produced by the pituitary gland.

Its most famous role is triggering ovulation.

Just before ovulation, LH rises dramatically in what is known as the LH surge.

 

LH and PCOS

LH becomes particularly interesting when evaluating possible PCOS.

 

In some women with PCOS:

• LH remains chronically elevated
• Ovarian androgen production increases
• Ovulation becomes irregular

A LH:FSH ratio greater than approximately 2:1 or 3:1 may suggest PCOS, although current diagnosis is never based on this ratio alone.

 

AMH: Anti-Müllerian Hormone

AMH is produced by small developing follicles within the ovaries.

Unlike FSH, AMH remains relatively stable throughout the cycle and can usually be measured at any time.

Because AMH reflects the number of small recruitable follicles, it has become one of the most commonly used markers of ovarian reserve.

 

Common Interpretive Ranges

• Above 3–4 ng/mL: high reserve, sometimes associated with PCOS or increased stimulation response
• 1–3 ng/mL: often considered within the expected range
• 0.5–1 ng/mL: reduced ovarian reserve
• Below 0.5 ng/mL: very low ovarian reserve

 

What AMH Can Tell You

AMH estimates egg quantity.

 

What AMH Does NOT Tell You

AMH does not tell you:

• Whether you will conceive naturally
• Whether you are ovulating
• The quality of individual eggs
• Whether implantation will occur
• Whether you will become pregnant this month

A low AMH does not mean pregnancy is impossible.

Likewise, a high AMH does not guarantee fertility.

AMH is best viewed as one piece of information rather than a prediction of future fertility.

 

 

Progesterone: Confirming Ovulation

Progesterone is produced by the corpus luteum after ovulation.

Its role is to prepare the uterine lining for implantation and support early pregnancy.

 

When Should Progesterone Be Tested?

The ideal timing is approximately:

7 days after ovulation

rather than simply “Day 21.”

The traditional Day-21 progesterone test only applies to women with a classic 28-day cycle who ovulate around Day 14.

 

Interpreting Progesterone

Many fertility specialists consider:

• Above 10 ng/mL: evidence that ovulation likely occurred
• Above 15 ng/mL: often associated with strong corpus luteum function

Low progesterone may suggest:

• Anovulation
• Suboptimal luteal function
• Incorrect testing timing

This is why ovulation tracking often improves interpretation.

 

Prolactin

Prolactin is best known for supporting breast milk production.

However, elevated prolactin can interfere with ovulation by suppressing reproductive hormones.

 

Causes of Elevated Prolactin

• Stress
• Poor sleep
• Certain medications
• Pituitary disorders

Interestingly, anxiety surrounding the blood draw itself can temporarily elevate prolactin levels.

An unexpected result is often repeated before further investigation.

Very elevated levels may warrant additional assessment of the pituitary gland.

 

Thyroid Hormones: TSH and Free T4

The thyroid and reproductive system are closely connected.

Even mild thyroid dysfunction may affect:

• Menstrual regularity
• Ovulation
• Implantation
• Pregnancy outcomes

TSH and Fertility

Although laboratory reference ranges often extend to 4–5 mIU/L, many fertility specialists prefer to see TSH below approximately 2.5 mIU/L when pregnancy is desired.

This does not mean a TSH of 3.0 automatically prevents pregnancy.

Rather, some clinicians consider optimization beneficial before conception.