Infertility (Female)

Female infertility is defined as the inability to achieve a clinical pregnancy after 12 months of regular unprotected sexual intercourse in women under 35, or after 6 months in women 35 and older. It is one of the most common reproductive health conditions globally, affecting approximately 1 in 6 couples — and in roughly 40–50% of cases where a couple cannot conceive, a female factor is identified as the primary or contributing cause.

Infertility is not a single disease but a clinical outcome with many possible underlying causes — spanning ovulatory dysfunction, structural abnormalities of the reproductive tract, endocrine disorders, immunological factors, and age-related decline in egg quality and ovarian reserve. In approximately 10–15% of cases, no identifiable cause is found despite thorough investigation — a category termed unexplained infertility.

Understanding the cause is the essential first step in treatment. The evaluation of female infertility relies heavily on blood testing — to assess ovarian reserve, ovulatory function, hormonal balance, and thyroid health — alongside imaging and where indicated, surgical assessment. A structured, systematic approach to investigation allows most causes to be identified and significantly increases the likelihood of successful treatment.

How Conception Normally Occurs

Understanding what normal conception requires makes it easier to understand where and why it can fail. For a pregnancy to occur, each of the following must happen:

The hypothalamic-pituitary-ovarian axis must function normally to drive follicular development and trigger ovulation
A mature egg must be released from the ovary (ovulation)
The fallopian tube must be patent (open) to allow the egg and sperm to meet
Sperm must successfully reach and fertilize the egg
The resulting embryo must travel to the uterus and implant in a receptive endometrium
The pregnancy must be hormonally supported (primarily by progesterone) through the early weeks

Female infertility can arise from failure at any of these steps. The most common categories — ovulatory dysfunction, tubal disease, uterine abnormalities, diminished ovarian reserve, and endocrine disorders — are outlined below.

Causes of Female Infertility

Ovulatory dysfunction (25–30% of female infertility)

Ovulatory dysfunction — irregular, infrequent, or absent ovulation — is the most common identifiable cause of female infertility. Without ovulation, no egg is available for fertilization. The major causes include:

Polycystic ovary syndrome (PCOS) — the single most common cause of anovulatory infertility, accounting for approximately 70% of ovulatory dysfunction cases. Characterized by androgen excess, insulin resistance, and irregular or absent ovulation.
Hypothalamic amenorrhea (HA) — suppression of the HPO axis due to energy deficit, excessive exercise, or stress; fully reversible with appropriate intervention
Hyperprolactinemia — elevated prolactin suppresses LH and FSH secretion, inhibiting ovulation
Thyroid dysfunction — both hypothyroidism and hyperthyroidism disrupt the menstrual cycle and ovulation; thyroid disease is one of the most common and most treatable causes of infertility
Premature ovarian insufficiency (POI) — loss of normal ovarian function before age 40; FSH is elevated and ovarian response is diminished
Diminished ovarian reserve — age-related or pathological reduction in the number and quality of remaining eggs

Tubal factor (20–30% of female infertility)

Blockage or damage to the fallopian tubes prevents sperm from reaching the egg or the fertilized embryo from reaching the uterus. The main causes are:

Pelvic inflammatory disease (PID) — most commonly from chlamydia or gonorrhoea infection; even a single episode of PID can cause significant tubal scarring
Endometriosis — endometrial tissue implants can damage the tubes and surrounding structures; severe endometriosis causes pelvic adhesions that impair tubal function
Previous pelvic or abdominal surgery — adhesions from surgery can distort tubal anatomy
Hydrosalpinx — fluid-filled, blocked fallopian tube; significantly reduces IVF success rates even when tubal disease is otherwise managed

Uterine and cervical factors (10–15% of female infertility)

Uterine fibroids (leiomyomas) — particularly submucosal fibroids that distort the uterine cavity and impair implantation
Endometrial polyps — benign growths of endometrial tissue that can impair implantation
Uterine septum or congenital abnormalities — structural malformations that affect embryo implantation or increase miscarriage risk
Asherman's syndrome — intrauterine adhesions (scar tissue) following uterine surgery or infection
Cervical stenosis or abnormal cervical mucus — impairs sperm transit

Endometriosis (up to 30–40% of infertile women)

Endometriosis — the presence of endometrial-like tissue outside the uterus — is found in a disproportionately high proportion of women with infertility. Its mechanisms are multiple: it can cause tubal damage and pelvic adhesions in moderate-to-severe disease, but even mild endometriosis impairs fertility through inflammatory mediators that affect egg quality, sperm function, and implantation. Endometriosis is often silent — diagnosed only during the infertility workup.

Diminished ovarian reserve and age

Female fertility declines progressively with age, reflecting both the reduction in the number of available eggs and — critically — the decline in egg quality. The decline accelerates significantly after age 35 and steeply after 40. This age-related decline is the reason that women 35 and older are advised to seek evaluation after 6 months rather than 12 months of trying to conceive.

Diminished ovarian reserve (DOR) can also occur in younger women due to genetic factors, prior ovarian surgery, chemotherapy, or endometriosis. AMH (anti-Müllerian hormone) is the primary blood marker used to assess ovarian reserve.

Unexplained infertility (10–15% of cases)

When standard investigation finds no identifiable cause — ovulation is occurring, tubes are patent, semen analysis is normal, and the uterine cavity is normal — the diagnosis is unexplained infertility. This does not mean nothing is wrong; it reflects the limits of current investigation rather than the absence of a problem. Subtle defects in egg or embryo quality, implantation, or immunological factors may be present but not detectable with standard testing.

The Fertility Investigation — Lab Testing

A structured hormonal evaluation is the foundation of the female infertility workup. The following tests are used to assess ovarian reserve, ovulatory function, hormonal balance, and potential endocrine causes.

Day 2–3 hormonal panel (early follicular phase)

Blood tests drawn on days 2–3 of the menstrual cycle (day 1 being the first day of full menstrual flow) reflect baseline pituitary and ovarian hormone levels before follicular development has begun. This timing is critical for accurate interpretation.

Marker	What it assesses	What elevated or abnormal results suggest
FSH	Ovarian reserve and pituitary drive	Elevated Day 3 FSH (>10–12 IU/L) suggests diminished ovarian reserve; very high FSH suggests POI
LH	Pituitary gonadotropin; LH:FSH ratio	Elevated LH relative to FSH (ratio >2) on Day 3 is associated with PCOS
Estradiol (E2)	Baseline follicular activity	Elevated Day 3 estradiol (>60–80 pg/mL) may indicate early follicular recruitment, masking a true elevated FSH; poor prognostic sign for IVF response
AMH (Anti-Müllerian Hormone)	Ovarian reserve — most stable marker; can be drawn any cycle day	Low AMH indicates diminished ovarian reserve; does not fluctuate with cycle phase, making it the most reliable single reserve marker

Mid-luteal progesterone (Day 21 in a 28-day cycle; 7 days post-ovulation)

A progesterone level drawn approximately 7 days after ovulation confirms whether ovulation occurred and assesses luteal phase adequacy. A level above 5 ng/mL (16 nmol/L) confirms ovulation occurred; levels above 10–15 ng/mL (32–48 nmol/L) suggest adequate luteal support. In women with irregular cycles, the test should be timed relative to estimated ovulation rather than fixed cycle day.

Additional hormonal markers

Marker	Role in fertility evaluation
TSH	Thyroid function — both hypothyroidism and hyperthyroidism impair fertility. TSH should be below 2.5 mIU/L for optimal fertility; subclinical hypothyroidism with TSH 2.5–4.5 is associated with reduced IVF success and increased miscarriage risk.
Prolactin	Screen for hyperprolactinemia — a common, treatable cause of anovulation and menstrual irregularity. Elevated prolactin suppresses GnRH and inhibits LH/FSH secretion.
Total and free testosterone	Screen for androgen excess (PCOS, congenital adrenal hyperplasia, adrenal tumors)
DHEA-S	Adrenal androgen; elevated in adrenal causes of androgen excess
SHBG	Sex hormone-binding globulin — affects free androgen levels; low in PCOS and insulin resistance
17-OH progesterone	Screen for non-classical congenital adrenal hyperplasia (CAH) — a cause of androgen excess and anovulation, often mistaken for PCOS
Fasting insulin and glucose / HOMA-IR	Assess insulin resistance — particularly relevant in PCOS; insulin resistance worsens ovulatory dysfunction and reduces treatment response
Vitamin D (25-OH)	Deficiency associated with reduced IVF success and impaired follicular development
CBC and iron studies (ferritin)	Iron deficiency is common in women with heavy periods; can impair overall health and fertility treatment tolerance
Antiphospholipid antibodies (aPL)	Screen for antiphospholipid syndrome — an immunological cause of recurrent miscarriage and implantation failure
Thyroid antibodies (TPO, anti-TG)	Thyroid autoimmunity is associated with increased miscarriage risk even with normal TSH
Karyotype	In women with recurrent miscarriage or suspected chromosomal cause

Imaging and procedural assessment

Transvaginal ultrasound — antral follicle count (AFC) as a marker of ovarian reserve; assessment of uterine morphology, endometrial thickness, fibroids, polyps, and ovarian cysts
Hysterosalpingogram (HSG) — X-ray assessment of tubal patency and uterine cavity; first-line structural investigation
Hysteroscopy — direct visualization of the uterine cavity; gold standard for diagnosing intrauterine pathology
Laparoscopy — definitive assessment for endometriosis, pelvic adhesions, and tubal disease; not performed routinely but essential when these are suspected

Ovarian Reserve — The Central Concept

Ovarian reserve refers to the quantity and quality of eggs remaining in the ovaries. It is one of the most important predictors of fertility treatment outcomes and spontaneous conception potential.

The two most widely used markers are:

AMH (Anti-Müllerian Hormone) — produced by small antral and preantral follicles; reflects the size of the remaining follicle pool. AMH does not fluctuate across the menstrual cycle and can be tested on any cycle day. It is the single best blood marker of ovarian reserve. Low AMH predicts poor ovarian response to stimulation in IVF and reduced natural fertility, though it does not predict egg quality independently of quantity.
Antral follicle count (AFC) — the number of small resting follicles visible on transvaginal ultrasound on Day 2–3 of the cycle; correlates strongly with AMH and predicts ovarian response to stimulation

Day 3 FSH and estradiol provide supplementary ovarian reserve information but are less reliable than AMH due to cycle-to-cycle variability.

Important caveat: Low ovarian reserve means fewer eggs available — but it does not mean zero eggs, nor does it mean the remaining eggs are of poor quality in younger women. Women with low AMH in their late 20s or early 30s may still have good-quality eggs and reasonable natural or assisted fertility, though time is more pressing than for women with normal reserve.

Key Endocrine Causes to Identify Early

Thyroid disease

Thyroid dysfunction is one of the most common and most easily treatable causes of female infertility and pregnancy loss. Both overt and subclinical hypothyroidism impair ovulation, implantation, and early pregnancy maintenance. Current fertility guidelines recommend a TSH target below 2.5 mIU/L when trying to conceive and below 2.5–3.0 mIU/L during early pregnancy. Even in women with normal TSH, thyroid peroxidase (TPO) antibodies — indicating autoimmune thyroiditis — are associated with increased miscarriage risk and reduced IVF success.

Hyperprolactinemia

Elevated prolactin suppresses GnRH pulsatility, reducing LH and FSH and inhibiting ovulation. It is a common, highly treatable cause of anovulation — dopamine agonist therapy (bromocriptine or cabergoline) normalizes prolactin and restores ovulatory cycles in the vast majority of affected women. Prolactin should be tested in all women with irregular periods or anovulatory infertility.

PCOS

PCOS is the single most common endocrine cause of female infertility. Management of PCOS-related infertility depends on body weight and insulin resistance status: lifestyle modification and weight loss (in overweight women) often restore ovulation; letrozole (an aromatase inhibitor) is first-line pharmacological ovulation induction; metformin improves insulin sensitivity and may restore ovulatory cycles; IVF is highly effective when simpler measures fail.

When to Seek Fertility Evaluation

Under 35: After 12 months of regular unprotected intercourse without pregnancy
35–39: After 6 months
40 and over: Promptly — without waiting 6 months — given the rapid decline in ovarian reserve with age
Any age, sooner, if: irregular or absent periods; known or suspected PCOS, endometriosis, or uterine abnormality; previous pelvic infection or surgery; history of cancer treatment; two or more pregnancy losses

Treatment Overview

Treatment is cause-directed. The most important initial step is identifying the underlying cause — because the right treatment for ovulatory dysfunction is fundamentally different from the right treatment for tubal disease or uterine pathology.

Ovulation induction

Letrozole — first-line agent for PCOS-related anovulatory infertility; lower multiple pregnancy risk than clomiphene
Clomiphene citrate — still widely used; blocks estrogen receptors in the hypothalamus, driving FSH release
Metformin — improves insulin sensitivity in PCOS; may restore ovulation alone or in combination with letrozole
Gonadotropins (injectable FSH/LH) — for women who do not respond to oral agents; requires close monitoring to minimize multiple pregnancy risk

Surgical treatment

Laparoscopic surgery for endometriosis, ovarian cysts, or pelvic adhesions
Hysteroscopic removal of fibroids, polyps, or intrauterine adhesions
Tubal surgery in selected cases (though IVF is often preferred when tubes are significantly damaged)

Assisted reproductive technology (ART)

Intrauterine insemination (IUI) — timed insemination of prepared sperm directly into the uterus; used in unexplained infertility, mild male factor, or cervical factor
In vitro fertilization (IVF) — eggs are retrieved after ovarian stimulation, fertilized in the laboratory, and the resulting embryo transferred to the uterus; the most effective ART for most causes of infertility
Intracytoplasmic sperm injection (ICSI) — a single sperm is injected directly into the egg; used when sperm quality is significantly impaired
Preimplantation genetic testing (PGT) — embryos tested for chromosomal abnormalities before transfer; reduces miscarriage rate and increases live birth rates, particularly in older women and those with recurrent miscarriage
Donor eggs — for women with severely diminished or absent ovarian reserve; achieves high pregnancy rates independent of maternal age

Recurrent Pregnancy Loss

Recurrent pregnancy loss (RPL) — defined as two or more clinical pregnancy losses — affects approximately 1–2% of couples trying to conceive and has an overlapping but distinct workup from primary infertility. Key investigations include:

Antiphospholipid antibodies (lupus anticoagulant, anticardiolipin, anti-β2 glycoprotein) — antiphospholipid syndrome is the most important treatable cause of RPL
Parental karyotype — chromosomal abnormalities in either partner explain a proportion of RPL
Uterine anatomy assessment (hysteroscopy or 3D ultrasound)
TSH and thyroid antibodies — both thyroid disease and autoimmunity increase miscarriage risk
Progesterone support in luteal phase — low progesterone is associated with early pregnancy loss; supplementation is widely used

Summary

Female infertility is a common condition with many possible underlying causes, each requiring a different diagnostic and treatment approach. The most common causes — ovulatory dysfunction (PCOS, hypothalamic amenorrhea, thyroid disease, hyperprolactinemia), tubal factor, endometriosis, uterine abnormalities, and diminished ovarian reserve — are identifiable with a structured investigation combining blood testing, ultrasound, and where indicated, surgical assessment.

Lab testing is central to this evaluation. AMH and antral follicle count assess ovarian reserve, Day 3 FSH and LH assess pituitary-ovarian dynamics, mid-luteal progesterone confirms ovulation, and TSH, prolactin, androgens, and insulin markers identify the endocrine causes that are among the most common and most treatable drivers of anovulatory infertility.

Treatment is highly effective for most causes of female infertility when the underlying diagnosis is made accurately. Tracking hormonal markers over time — particularly through a fertility investigation and treatment cycle — provides the longitudinal context needed to interpret results and adjust management with precision.

FAQ: Infertility (Female)

How is female infertility defined?

Female infertility is defined as the inability to achieve a clinical pregnancy after 12 months of regular unprotected intercourse in women under 35, or after 6 months in women 35 and older. Women 40 and over should seek evaluation promptly without waiting 6 months, given the rapid age-related decline in egg quantity and quality. Earlier evaluation is appropriate at any age if there is a known risk factor such as irregular periods, endometriosis, prior pelvic infection, or previous pregnancy loss.

What are the most common causes of female infertility?

The most common causes are ovulatory dysfunction (including PCOS, hypothalamic amenorrhea, thyroid disease, and hyperprolactinemia), tubal damage (most often from pelvic infections or endometriosis), uterine or cervical abnormalities, endometriosis, and diminished ovarian reserve. In approximately 10–15% of cases, no cause is found despite thorough investigation — termed unexplained infertility. Female factors account for approximately 40–50% of infertility cases; male factors account for a similar proportion.

What blood tests are done for female infertility?

The core fertility panel includes AMH (ovarian reserve, can be drawn any cycle day), Day 3 FSH and LH (pituitary-ovarian function), Day 3 estradiol (baseline follicular activity), mid-luteal progesterone (confirms ovulation), TSH (thyroid function), and prolactin (screen for hyperprolactinemia). Additional tests depending on clinical picture include testosterone, DHEA-S, SHBG, 17-OH progesterone, fasting insulin and glucose, vitamin D, iron studies, thyroid antibodies, and antiphospholipid antibodies.

What is AMH and why does it matter for fertility?

AMH (Anti-Müllerian Hormone) is the most reliable blood marker of ovarian reserve — the quantity of eggs remaining in the ovaries. It is produced by small ovarian follicles and reflects the size of the remaining egg pool. Unlike FSH and estradiol, AMH does not fluctuate across the menstrual cycle and can be tested on any day. Low AMH indicates diminished ovarian reserve and predicts reduced response to IVF stimulation. However, low AMH in a younger woman does not necessarily mean poor egg quality — it means fewer eggs and less time, not zero chance.

What is a normal Day 3 FSH for fertility?

A Day 3 FSH below 10 IU/L is generally considered normal. Values between 10–15 IU/L suggest diminished ovarian reserve and reduced response to ovarian stimulation. Values above 15–20 IU/L are associated with significantly reduced fertility and poor IVF response. Very high FSH (above 25–40 IU/L) suggests premature ovarian insufficiency. Day 3 FSH must always be interpreted alongside Day 3 estradiol — an apparently normal FSH with elevated estradiol may falsely reassure, as the elevated estradiol is suppressing FSH through negative feedback.

What TSH level is recommended when trying to conceive?

Current fertility guidelines recommend maintaining TSH below 2.5 mIU/L when actively trying to conceive. Subclinical hypothyroidism — TSH between 2.5 and 4.5 with normal free T4 — is associated with reduced IVF success rates and increased miscarriage risk. Even women with TSH within the standard laboratory reference range (which often extends to 4.0–5.0 IU/L) may benefit from treatment if they are trying to conceive or undergoing IVF. Thyroid peroxidase (TPO) antibodies also increase miscarriage risk independently of TSH level.

Does PCOS cause infertility?

Yes — PCOS is the most common cause of anovulatory infertility, accounting for approximately 70% of ovulatory dysfunction cases. In PCOS, the hormonal imbalance (elevated LH, insulin resistance, androgen excess) disrupts the normal follicular maturation and LH surge that trigger ovulation. However, PCOS-related infertility is also among the most treatable — ovulation induction with letrozole, lifestyle modification, and where needed IVF are all highly effective. The vast majority of women with PCOS who want to conceive can do so with appropriate treatment.

What is the role of progesterone in female fertility?

Progesterone is produced by the corpus luteum after ovulation and is essential for preparing the endometrium for implantation and supporting early pregnancy. A mid-luteal progesterone level (drawn approximately 7 days after ovulation) confirms that ovulation occurred. Levels above 5 ng/mL confirm ovulation; levels above 10–15 ng/mL suggest adequate luteal function. Low luteal phase progesterone may contribute to implantation failure and early pregnancy loss, and progesterone supplementation is widely used in IVF cycles and in women with recurrent miscarriage.

What is unexplained infertility?

Unexplained infertility is the diagnosis given when standard investigation — ovulation confirmed, tubes patent, semen analysis normal, uterine cavity normal — finds no identifiable cause. It affects approximately 10–15% of infertile couples. It does not mean nothing is wrong; it reflects the limits of current testing. Subtle abnormalities in egg quality, fertilization, early embryo development, or implantation may be present but undetectable with standard investigation. Treatment options for unexplained infertility include IUI, ovulation induction, and IVF — which bypasses many of the steps where undetected failure may be occurring.

Does endometriosis cause infertility?

Yes. Endometriosis is found in 30–40% of infertile women — a significantly higher prevalence than in the general population (approximately 10%). It impairs fertility through multiple mechanisms: in moderate-to-severe disease, it causes tubal damage and pelvic adhesions; even in mild disease, inflammatory mediators from endometrial implants impair egg quality, sperm function, and endometrial receptivity. Endometriosis is often asymptomatic and is frequently diagnosed only during a fertility investigation.

How does age affect female fertility?

Female fertility declines progressively with age, driven primarily by the reduction in the number and quality of eggs. The decline is gradual through the 20s, accelerates after 35, and becomes steep after 40. After 40, the rate of chromosomally abnormal eggs rises significantly, increasing miscarriage rates and reducing the likelihood of successful IVF per cycle. AMH levels fall with age, reflecting shrinking ovarian reserve. Age is the single most important predictor of fertility treatment outcome, which is why earlier investigation is recommended for women 35 and over.

What is recurrent pregnancy loss and how is it different from infertility?

Recurrent pregnancy loss (RPL) is defined as two or more clinical pregnancy losses and has a partly distinct workup from primary infertility. Key investigations include antiphospholipid antibodies (the most important treatable cause of RPL), parental karyotype, uterine anatomy assessment, TSH and thyroid antibodies, and progesterone assessment. Antiphospholipid syndrome — an autoimmune condition causing abnormal blood clotting — is the most important cause to identify because it is highly treatable with aspirin and heparin, dramatically improving live birth rates.