Unexplained Infertility: What It Means and What to Do Next

What does a ‘normal’ fertility workup actually test?

A standard fertility evaluation systematically assesses the most common and detectable causes of infertility.

• Ovarian reserve: AMH (anti-Müllerian hormone), day-3 FSH and estradiol, and an antral follicle count by ultrasound assess the quantity and hormonal context of remaining eggs 1Ref 1Practice Committee of the American Society for Reproductive Medicine (2021).Fertility evaluation of infertile women: a committee opinion.Standard fertility evaluation framework, timing thresholds for specialist referral (12 months under 35, 6 months at 35+), and the unexplained infertility diagnosis
• Ovulatory function: Cycle tracking, progesterone level, and sometimes an LH surge test confirm ovulation is occurring
• Uterine cavity: A sonohysterogram, hysteroscopy, or hysterosalpingogram (HSG) looks for fibroids, polyps, or abnormalities inside the uterine cavity
• Fallopian tubes: An HSG evaluates whether the tubes are open (patent)
• Sperm: A semen analysis assesses count, motility, and morphology

When all of these return within normal parameters but conception has not occurred after the expected interval — generally 12 months under age 35, or 6 months at age 35 or older — the label ‘unexplained infertility’ applies 1Ref 1Practice Committee of the American Society for Reproductive Medicine (2021).Fertility evaluation of infertile women: a committee opinion.Standard fertility evaluation framework, timing thresholds for specialist referral (12 months under 35, 6 months at 35+), and the unexplained infertility diagnosis. Unexplained infertility accounts for roughly 10 to 30 percent of cases referred to reproductive specialists.

The limitation of ‘normal’ testing is real: it does not capture egg quality, sperm DNA fragmentation, embryo chromosome quality, endometrial receptivity at a molecular level, or subtle immune and peritoneal factors. These are active areas of research.

Why might I not be conceiving if everything looks normal?

Several mechanisms may contribute to unexplained infertility that standard testing does not capture:

Egg quality. Ovarian reserve tests measure the quantity of eggs available, not their quality. Subtle decrements in egg quality — particularly chromosomal abnormalities that become more common with advancing age — may result in embryos that do not implant or that miscarry early.

Sperm DNA fragmentation. A standard semen analysis does not assess sperm DNA integrity. Higher levels of fragmentation are associated with difficulty conceiving and increased early pregnancy loss in some research, and additional testing is sometimes recommended in the unexplained infertility workup 2Ref 2Practice Committee of the American Society for Reproductive Medicine (2020).Evidence-based treatments for couples with unexplained infertility: a guideline.Evidence-based treatment options for unexplained infertility including expectant management, IUI with ovarian stimulation, and IVF; IVF as most effective single-cycle treatment.

Endometrial receptivity. Even a structurally normal uterus may have suboptimal molecular signaling for implantation in some cycles. Tests for this exist (such as the ERA test) but their clinical utility remains actively debated.

Subtle endometriosis or peritoneal factors. Minimal or mild endometriosis may not show on imaging but can affect tubal function, egg quality, or the uterine environment. A 2024 systematic review found endometriosis was identified in a substantial proportion of patients previously labeled unexplained when laparoscopy was performed 3Ref 3Van Gestel H, Bafort C, Meuleman C, Tomassetti C, Vanhie A (2024).The prevalence of endometriosis in unexplained infertility: a systematic review.Endometriosis found in a substantial proportion of patients previously classified with unexplained infertility when laparoscopic evaluation is performed.

For most couples, the cause likely involves a combination of factors rather than a single identifiable issue.

What treatment options does the evidence support?

ASRM guidance provides a clear framework for evidence-based treatment of unexplained infertility 2Ref 2Practice Committee of the American Society for Reproductive Medicine (2020).Evidence-based treatments for couples with unexplained infertility: a guideline.Evidence-based treatment options for unexplained infertility including expectant management, IUI with ovarian stimulation, and IVF; IVF as most effective single-cycle treatment:

Expectant management. For younger patients (under 35) with a shorter duration of infertility, continued natural attempts for a defined period is reasonable. Cumulative conception rates increase over time, though monthly probability is lower than for fertile couples.

IUI with ovarian stimulation. Intrauterine insemination (IUI) combined with mild stimulation using clomiphene or letrozole increases the number of eggs available and places a prepared sperm sample directly into the uterus. It is less invasive and less expensive than IVF. A 2024 individual patient data meta-analysis of four randomized controlled trials found that cumulative live birth rates from IUI with ovarian stimulation were not significantly different from IVF (43.2% versus 50.3%; HR 1.19, 95% CI 0.81–1.74), supporting IUI as a legitimate first-line option in appropriately selected patients 4Ref 4Lai S, Wang R, van Wely M, Costello M, Farquhar C, Bensdorp AJ, Custers IM, Goverde AJ, Elzeiny H, Mol BW, Li W (2024).IVF versus IUI with ovarian stimulation for unexplained infertility: a collaborative individual participant data meta-analysis.Cumulative live birth rates not significantly different between IVF and IUI with ovarian stimulation over equivalent treatment periods (50.3% vs 43.2%, HR 1.19, 95% CI 0.81–1.74) in four RCTs of 908 women with unexplained infertility.

IVF. In vitro fertilization remains the most effective single-cycle treatment 2Ref 2Practice Committee of the American Society for Reproductive Medicine (2020).Evidence-based treatments for couples with unexplained infertility: a guideline.Evidence-based treatment options for unexplained infertility including expectant management, IUI with ovarian stimulation, and IVF; IVF as most effective single-cycle treatment. It bypasses several of the steps that may be failing — fertilization, early embryo development, and initial tube transport — and when embryo quality can be assessed, it provides additional diagnostic information. Success rates depend heavily on age.

PGT-A with IVF. When IVF is undertaken, preimplantation genetic testing for aneuploidies (PGT-A) allows embryos to be screened for chromosomal abnormalities before transfer, potentially improving implantation rates per transfer in appropriate candidates.

The choice of treatment involves weighing your age, how long you have been trying, emotional and financial capacity, and how urgently you want to pursue the most effective option. A reproductive endocrinologist is the right partner for this decision 1Ref 1Practice Committee of the American Society for Reproductive Medicine (2021).Fertility evaluation of infertile women: a committee opinion.Standard fertility evaluation framework, timing thresholds for specialist referral (12 months under 35, 6 months at 35+), and the unexplained infertility diagnosis.

When to see a specialist and how quickly to escalate

ASRM and most professional societies recommend:

• Under 35: Evaluation after 12 months of unprotected intercourse without conception
• Age 35–39: Evaluation after 6 months
• Age 40 and older: Prompt evaluation without a defined waiting period
• Known relevant history (prior pelvic surgery, PCOS, endometriosis, irregular cycles, abnormal semen analysis): Earlier evaluation is appropriate regardless of age or duration 1Ref 1Practice Committee of the American Society for Reproductive Medicine (2021).Fertility evaluation of infertile women: a committee opinion.Standard fertility evaluation framework, timing thresholds for specialist referral (12 months under 35, 6 months at 35+), and the unexplained infertility diagnosis

A reproductive endocrinologist (RE) is the specialist trained to evaluate and treat unexplained infertility. If you have already had a basic workup through a primary care provider or OB-GYN, the RE visit typically involves reviewing those results, considering additional testing, and developing a treatment plan tailored to your age and history.

What questions should I ask my reproductive endocrinologist?

Going into your appointment prepared can make the conversation more productive:

• Given my age and how long we have been trying, what treatment do you recommend as a first step?
• Are there additional tests worth considering — sperm DNA fragmentation, ERA, or a repeat HSG?
• What is a realistic success rate with IUI versus IVF at my age and given our history?
• If we start with IUI, how many cycles would you recommend before moving to IVF?
• Would PGT-A be relevant for us if we pursue IVF?
• Are there lifestyle factors worth addressing before or during treatment?

Gale can help you organize your questions and prepare for a specialist visit if you have not yet seen a reproductive endocrinologist, or help you think through next steps with a primary care clinician.