Pregnancies that stop before you even know they exist

There are pregnancies that begin without ever becoming visible. Real biological beginnings, but too early to be clinically perceived. And yet, everything starts perfectly: fertilisation, cell divisions, migration… before the process silently comes to an end.

This is a fundamental reality of human reproduction: a large proportion of pregnancies do not progress beyond the very first stages.

An invisible construction, step by step

From the moment of fertilisation, a new organism begins to form. The oocyte and sperm fuse, giving rise to an embryo that rapidly divides. Within just a few days, it becomes a morula and then a blastocyst.

📌 At this stage:

• no clinical signs

• no specific sensations

• no possible detection

The embryo then travels through the fallopian tube towards the uterus, a discreet but crucial journey. Everything depends on an extremely precise timing between the embryo and the endometrium.

Implantation: the decisive moment

It is at implantation that pregnancy becomes biologically active. The embryo embeds itself into the endometrium and begins an immunological and hormonal dialogue with the mother.

If this step is successful, a hormone appears: hCG.

• Detectable in blood: approximately 8–10 days after ovulation

• Detectable in urine: approximately 10–14 days

But at this stage, everything remains fragile. A pregnancy may still stop without any symptoms, sometimes even before a missed period.

Biochemical pregnancies: when everything stops before becoming visible

Some pregnancies are only detected through a positive blood test, then disappear before any ultrasound evidence can be seen. These are called biochemical pregnancies.

📌 Estimated frequency:

• around 30–50% of human conceptions

• often mistaken for a slightly delayed period

In most cases, the person is not even aware that an embryo had implanted.

Why are these early losses so frequent?

In the majority of cases, the cause is simple but decisive: spontaneous chromosomal abnormalities in the embryo. Nature performs a very early selection here.

However, other factors may also contribute. The endometrium must be perfectly receptive at the time of implantation — a short, finely tuned “window”.

When this synchronisation is disrupted, implantation fails.

Other contributing factors may include:

• hormonal imbalances (especially progesterone)

• endometrial inflammation

• immunological factors

• rare uterine abnormalities

  
  

In vitro fertilisation: a more visible phenomenon

In IVF, these mechanisms become more measurable. Despite good-quality embryos being transferred into the uterus, not all implant.

📌 In practice:

• implantation rate: approximately 30–60%

• strongly dependent on age and embryo quality

Even a morphologically perfect embryo under the microscope may fail to implant, as morphology does not guarantee genetic normality nor synchronisation with the endometrium.

What is really happening

It is essential to understand that these very early failures are not “lost pregnancies” in the traditional sense. They are often biological attempts interrupted at a stage where pregnancy has not yet clinically existed.

One could say that most selection occurs before pregnancy even becomes visible.

Conclusion

Between fertilisation and a detectable pregnancy lies an invisible zone where biology continuously tests, selects, and adjusts. This phase is silent, yet fundamental.

Understanding this helps place these events in their true context: not as dramatic exceptions, but as a normal — albeit often unknown — part of human reproductive physiology.

Take care of yourself.

Kind regards,

Dr. Sandra Yene Amougui