Understanding Female Fertility
Female fertility is determined by several interconnected biological systems — the ovarian reserve (how many eggs you have), hormonal balance, uterine health, and tubal patency. Understanding these helps you make informed decisions about your reproductive health.
What Is Ovarian Reserve?
Ovarian reserve refers to the quantity and quality of eggs (oocytes) remaining in your ovaries. You are born with approximately 1–2 million eggs; by puberty this falls to around 300,000, and it continues to decline throughout your reproductive life.
Key ovarian reserve tests (ASRM 2023):
- Anti-Müllerian Hormone (AMH): The most reliable marker of ovarian reserve. Produced by small follicles, AMH remains stable throughout the menstrual cycle and can be tested any day. Normal range: 1.0–3.5 ng/mL. Low AMH (<1.0 ng/mL) suggests diminished reserve; high AMH (>3.5 ng/mL) may indicate PCOS.
- Antral Follicle Count (AFC): An ultrasound count of resting follicles in both ovaries. Normal AFC: 8–15 total. Low AFC (<5) indicates diminished reserve; high AFC (>20) may indicate PCOS. ASRM 2023 considers AFC + AMH together for the most accurate assessment.
- Follicle-Stimulating Hormone (FSH): Measured on cycle day 2–3. Elevated FSH (>10 IU/L) suggests the pituitary is working harder to stimulate the ovaries — a sign of diminished reserve. However, FSH can vary cycle to cycle.
- Estradiol (E2): Also measured on cycle day 2–3 alongside FSH. Elevated E2 (>60–80 pg/mL) can suppress FSH artificially, masking a high reading and indicating poor reserve.
The Menstrual Cycle and Ovulation
A normal menstrual cycle ranges from 21 to 35 days (ASRM 2023). The cycle has two phases:
Follicular phase (days 1–14 in a 28-day cycle): FSH stimulates several follicles to grow. One follicle becomes dominant and produces increasing amounts of estrogen. When estrogen peaks, it triggers an LH surge, leading to ovulation approximately 24–36 hours later.
Luteal phase (days 15–28): The ruptured follicle becomes the corpus luteum, producing progesterone to prepare the uterine lining for implantation. If no pregnancy occurs, progesterone falls, the lining sheds, and menstruation begins.
Ovulation window: The fertile window is approximately 5 days before ovulation and the day of ovulation. An egg survives 12–24 hours after release; sperm can survive 3–5 days in the female reproductive tract.
Hormones That Govern Fertility
| Hormone | Role | When to Test |
|---|---|---|
| FSH | Stimulates follicle growth | Day 2–3 |
| LH | Triggers ovulation | Day 2–3, midcycle |
| Estradiol (E2) | Grows endometrium | Day 2–3 |
| Progesterone | Supports early pregnancy | Day 21 |
| AMH | Ovarian reserve marker | Any day |
| Thyroid (TSH, T4) | Regulates metabolism + cycle | Any day |
| Prolactin | May suppress ovulation if elevated | Any day |
What Affects Female Fertility?
Age is the most significant factor. Egg quality — not just quantity — declines with age. Per ASRM 2023:
- Age 20–30: ~25% chance of conception per cycle
- Age 35: ~15–20% per cycle
- Age 40: ~5% per cycle
- Age 43+: <3% per cycle with own eggs
Other key factors:
- Polycystic ovary syndrome (PCOS) — affects 6–12% of reproductive-age women
- Endometriosis — found in 10% of women; damages eggs and tubes
- Tubal damage — from infections (chlamydia, PID) or previous surgery
- Uterine abnormalities — fibroids, polyps, septum, Asherman's syndrome
- Thyroid disorders — even subclinical hypothyroidism affects implantation
- BMI — both underweight (BMI <18.5) and overweight (BMI >30) reduce conception rates
- Smoking — halves fertility and doubles miscarriage risk (ASRM 2023)
- Stress — severe chronic stress may disrupt the HPO axis and suppress ovulation
When Should You Seek Evaluation?
Per ASRM 2023 guidelines:
- Under 35: After 12 months of regular unprotected intercourse
- Age 35–40: After 6 months
- Over 40: Seek evaluation immediately
- Any age: If you have known risk factors (irregular cycles, PCOS diagnosis, previous STIs, endometriosis, prior surgery, or a family history of early menopause)
Fertility Preservation
If you are not ready to conceive but want to preserve options, egg freezing (oocyte cryopreservation) is the most effective method. ASRM lifted the "experimental" label from egg freezing in 2012. Per ESHRE 2023 guidelines, frozen egg survival rates with vitrification exceed 80%, and live birth rates per thaw cycle are 40–50% in women under 35 who freeze ≥10 mature eggs.
The Bottom Line
Female fertility is complex but increasingly measurable and treatable. A basic fertility workup — AMH, AFC, FSH, E2, thyroid, and a pelvic ultrasound — can be completed in a single menstrual cycle and provides a comprehensive picture of your reproductive health.
Reference: ASRM Practice Committee — Fertility Evaluation of Infertile Women, 2021. ESHRE Guideline: Ovarian Stimulation for IVF/ICSI, 2019 (updated 2023).
Frequently Asked Questions
What is a normal AMH level for fertility?▾
Normal AMH for fertility is 1.0–3.5 ng/mL. Values below 1.0 ng/mL suggest diminished ovarian reserve. Values above 3.5 ng/mL may indicate PCOS. AMH can be tested on any day of the cycle.
At what age does female fertility decline most rapidly?▾
Female fertility declines gradually from the late 20s, more noticeably from age 35, and significantly after age 37–38. By age 40, monthly conception rates fall below 5% per cycle due to egg quality decline. ASRM recommends seeking evaluation after 6 months of trying at age 35–40.
Can you get pregnant with low ovarian reserve?▾
Yes — low ovarian reserve reduces the number of eggs available but does not make conception impossible. Many women with low AMH conceive naturally or with IVF. IVF outcome depends more on egg quality (which correlates with age) than on quantity alone.
How do I know if I am ovulating?▾
Signs of ovulation include mid-cycle cervical mucus changes (clear, stretchy, egg-white consistency), a slight rise in basal body temperature, and a positive LH test. A blood progesterone test on day 21 of a 28-day cycle (>3 ng/mL) confirms ovulation occurred.