Why do so many women get pregnant… when they thought they were infertile?

This is a common story in consultation: a woman presents with a diagnosis of infertility, sometimes established years ago, sometimes after multiple treatment attempts… and yet, she becomes pregnant spontaneously.

At first glance, this may seem paradoxical. In reality, human fertility does not follow a binary logic. It is not a matter of being “fertile” or “infertile,” but rather a continuum of probabilities, sometimes very low… but rarely zero.

What is infertility, exactly?

Medically, infertility is defined as the absence of pregnancy after 12 months of regular unprotected intercourse, or after 6 months in women over 35 or in the presence of risk factors.

It is essential to understand that this is a statistical definition, not a diagnosis of definitive sterility.

Moreover, infertility is a couple-related condition:

• approximately 30% female factor

• 30% male factor

• 30% combined factors

• 10% unexplained

👉 An evaluation focusing only on the woman is therefore often insufficient.

Even after IVF: why spontaneous pregnancy is still possible

Even in patients who have failed multiple IVF attempts, spontaneous pregnancy can occur.

This is neither a “miracle” nor a diagnostic error.

It is simply biology:👉 millions of sperm cells,👉 one oocyte,👉 and a probability that is extremely low… but real.

Human fertilization is an exceptionally complex process:

• natural selection of sperm cells

• sperm–oocyte interaction

• early embryonic development

• implantation in a receptive endometrium

👉 IVF optimizes some of these steps, but does not perfectly replicate natural physiology.

IVF improves conditions, but it does not guarantee success.Conversely, nature can sometimes succeed where medicine fails — not because there is no underlying problem, but because even a very small probability may eventually materialize.

Low AMH ≠ inability to conceive

AMH is frequently misunderstood.

It reflects quantitative ovarian reserve, but does not directly predict:

• oocyte quality

• or the short-term ability to conceive naturally

👉 A low AMH indicates reduced probability, not zero probability.

Irregular cycles ≠ sterility

Irregular cycles make timing more difficult, but:

• ovulation may still occur

• sometimes unpredictably

• yet sufficiently to allow conception

👉 Again: reduced probability ≠ impossibility.

The role of time… and stress

Stress is not the sole cause of infertility, but it can:

• disrupt hormonal regulation

• reduce frequency of intercourse

• indirectly affect chances of conception

In some cases, pregnancies occur after:

• a release of pressure

• a change in environment

• or a pause in treatment

👉 Not because “it is all psychological,” but because the reproductive system is sensitive to the overall physiological context.

When to seek medical advice

Even though spontaneous pregnancy remains possible, it is important not to lose time:

👉 Consult after:

• 12 months of trying

• 6 months if over 35

• earlier in case of risk factors

• 
  

The key message

A diagnosis of infertility does not mean zero chance.

👉 In most cases, it means:a reduced probability — sometimes very low… but rarely zero.

It is precisely within this narrow, uncertain space that these “unexpected” pregnancies occur.

Conclusion

When some women become pregnant “against all expectations,” it is neither an error nor a miracle.

It is the most fundamental expression of reproductive biology:👉 an imperfect, variable, probabilistic system

…where sometimes, a small probability is enough.

As a gynecologist, I always remind my patients that in matters of fertility, even a low probability remains a real possibility — one that deserves to be understood without creating false hope, but also without being dismissed.

Take care of yourself.

Kind regards,

Dr. Sandra Yene Amougui