Fertility is not just about anatomy—it’s deeply rooted in the delicate balance of hormones that control your menstrual cycle, ovulation, and ability to conceive. When these hormones are out of sync, it can lead to irregular cycles, difficulty ovulating, or challenges maintaining a pregnancy. In this guide, we’ll explain how hormone levels affect fertility, and break down the key hormone tests your doctor may order during a fertility evaluation.
Why Hormones Are Central to Reproductive Health
Hormones are chemical messengers that regulate critical reproductive processes, including:
- Follicle development and egg maturation
- Ovulation (release of the egg)
- Thickening of the uterine lining
- Implantation of a fertilized embryo
- Menstrual bleeding
Even subtle imbalances in these hormones can disrupt ovulation or prevent conception. That’s why fertility testing typically starts with hormonal bloodwork.
Key Hormones and Their Role in Fertility
1. FSH (Follicle-Stimulating Hormone)
- When Tested: Cycle days 2–5
- Normal Range: Varies by lab and age, typically 3–10 mIU/mL in reproductive-age women
- What It Does: Stimulates the growth of ovarian follicles (which contain eggs) early in the menstrual cycle.
- Why It Matters: High FSH levels can indicate diminished ovarian reserve, meaning fewer eggs are available for fertilization. A high FSH level signals the body is working harder to stimulate the ovaries, often seen with aging or premature ovarian insufficiency.
2. LH (Luteinizing Hormone)
- When Tested: Cycle days 2–5 and around ovulation
- Normal Range: 1.9–12.5 mIU/mL (early cycle); surge >20–40 mIU/mL near ovulation
- What It Does: Triggers ovulation (the release of the egg) mid-cycle.
- Why It Matters: LH is usually low early in the cycle and spikes right before ovulation. Elevated baseline LH, particularly when higher than FSH, may indicate Polycystic Ovary Syndrome (PCOS). Lack of a surge can suggest anovulation (failure to ovulate).
3. AMH (Anti-Müllerian Hormone)
- When Tested: Any time during the cycle
- Normal Range: 1.0–4.0 ng/mL for women of reproductive age
- What It Does: Reflects the number of small follicles in the ovaries—a marker of ovarian reserve.
- Why It Matters: Low AMH suggests a low number of eggs remaining. High AMH may indicate PCOS, where there are many small follicles but irregular ovulation.
4. Estradiol (E2)
- When Tested: Cycle days 2–5 and mid-cycle
- Normal Range: <75 pg/mL (early follicular phase)
- What It Does: Estradiol is a form of estrogen that supports follicle growth, prepares the uterine lining, and works with LH to trigger ovulation.
- Why It Matters: Elevated E2 early in the cycle can artificially suppress FSH and mask poor ovarian reserve. Low mid-cycle E2 may indicate problems with follicle development.
5. Progesterone
- When Tested: 5–7 days after ovulation (usually around cycle day 21)
- Normal Range: >10 ng/mL during the luteal phase indicates ovulation
- What It Does: Stabilizes the uterine lining and supports early pregnancy.
- Why It Matters: Low progesterone in the second half of the cycle can indicate a luteal phase defect, potentially affecting implantation and increasing miscarriage risk.
6. Prolactin
- When Tested: Early in the cycle (fasting preferred)
- Normal Range: 5–25 ng/mL
- What It Does: Mainly responsible for breast milk production, but also affects reproductive hormones.
- Why It Matters: High prolactin levels can inhibit FSH and LH, leading to anovulation or irregular periods. This can be caused by stress, medications, or pituitary gland disorders like a prolactinoma.
7. TSH (Thyroid-Stimulating Hormone)
- When Tested: Any time in the cycle
- Optimal Range for Fertility: 1.0–2.5 mIU/L
- What It Does: Regulates the thyroid gland, which plays a major role in metabolism and hormonal balance.
- Why It Matters: Both hypothyroidism (underactive thyroid) and hyperthyroidism can disrupt ovulation and increase miscarriage risk. TSH testing helps assess if thyroid function is affecting fertility.
8. Free T4 and T3
- Why It Matters: These provide additional detail if TSH is abnormal, helping to identify thyroid disorders more accurately.
9. Androgens (Testosterone, DHEA-S)
- Why It Matters: Elevated androgen levels are common in PCOS and can interfere with follicle maturation, ovulation, and overall hormonal harmony. Symptoms often include acne, hair thinning, or excessive hair growth.
What Do Abnormal Hormone Levels Mean?
| Hormone | Too High May Indicate | Too Low May Indicate |
|---|---|---|
| FSH | Poor ovarian reserve | Pituitary dysfunction |
| LH | PCOS | Hypothalamic amenorrhea |
| AMH | PCOS | Diminished ovarian reserve |
| Estradiol | Poor egg quality, PCOS | Poor follicle growth |
| Progesterone | Rare | Anovulation, luteal defect |
| Prolactin | Pituitary tumor, stress | Rare, but can disrupt cycles |
| TSH | Hypothyroidism | Hyperthyroidism |
How Hormone Testing Fits Into a Fertility Evaluation
Hormone testing is typically the first step in a fertility evaluation and is often combined with:
- Ultrasound to assess ovarian follicles and uterine health
- Ovulation tracking with basal body temperature or LH surge kits
- Hysterosalpingography (HSG) to check fallopian tube patency
- Partner semen analysis to assess male fertility
When to Consider Hormone Testing
You should consider hormone testing if you:
- Have irregular, infrequent, or absent periods
- Have been trying to conceive for 6–12 months without success
- Are over 35 and want to assess egg reserve
- Have a history of miscarriage or hormonal disorders like PCOS or thyroid issues
- Are considering fertility preservation (e.g., egg freezing)
Final Thoughts
Hormones orchestrate every stage of the fertility process. A targeted hormone evaluation offers critical insights into what’s happening inside your body and helps guide the best fertility treatments—whether that’s natural conception, ovulation induction, IUI, or IVF.
