Biochemical pregnancy: a positive test that doesn’t hold

‘Biochemical’: the term feels cold when describing what patients go through. You saw a positive result, you started to believe in it, then the second test result came back lower. First of all, I want to say this: it is a loss, and it deserves to be treated as such. Secondly, it is helpful to understand what it means.

Definition

A biochemical pregnancy is when the beta-hCG becomes positive but then drops before a pregnancy is visible on an ultrasound scan — that is, before the gestational sac appears, at around 5 to 6 weeks of pregnancy. The embryo began to implant and produce hCG, but its development then stopped.

The European Society of Human Reproduction and Embryology (ESHRE) prefers to use the term ‘biochemical pregnancy loss’ and classifies it as an early miscarriage.

Is it common?

Very common. In natural conception, many go unnoticed: they resemble a slightly late period. In IVF, because hCG levels are routinely measured, all such cases are detected. According to studies, they account for approximately 10 to 20 per cent of positive tests following a transfer, with the frequency increasing with the age of the eggs.

Why does this happen?

The main cause is the same as for most early miscarriages: a chromosomal abnormality in the embryo, present from the moment of fertilisation. It is not due to anything you have done or failed to do. Less commonly, uterine factors (polyps, endometritis, septum), hormonal factors (thyroid imbalance, insufficient luteal support) or, in rare cases, antiphospholipid syndrome may be involved.

What a biochemical pregnancy is not: the result of physical exertion, air travel, sexual intercourse or everyday stress.

What it tells you about your chances

This is the point doctors often emphasise, and it is correct: a biochemical pregnancy indicates that an embryo was able to begin to implant. Several studies have found that patients who have had a biochemical pregnancy have, in their next cycle, chances of a live birth that are at least comparable — and sometimes better — than those whose test remained negative. This is not a consolation, but it is a fact.

Should you undergo further investigations?

After a single biochemical pregnancy, generally not: this is a common occurrence and is usually an isolated incident. Further investigations may be considered:

• after two or more pregnancy losses, including biochemical pregnancies, according to the 2022 ESHRE definition;
• in the event of repeated failures following the transfer of good-quality embryos;
• if a previous examination of the uterine cavity has never been carried out.

The assessment usually includes an examination of the uterine cavity (3D ultrasound or hysteroscopy), the thyroid, testing for antiphospholipid antibodies and, in some cases, a karyotype for the couple. PGT-A is sometimes recommended; its value depends largely on age. I also discuss this in the article on implantation failure.

When to try again?

Physically, it is not usually necessary to wait more than one cycle: you wait for your period to return and for the hCG to become negative. A frozen embryo transfer can often be scheduled for the very next cycle. Emotionally, however, there is no universal ‘right’ timeframe. Some patients want to try again straight away; others need two or three months. Both approaches are valid.

What I’ve observed

A biochemical pregnancy is often downplayed by those around you, because it ‘didn’t really happen’. Patients, however, have often already imagined a due date. Talk about it – with your partner, a friend or a professional if needed. What remains unsaid weighs more heavily on the next transfer.

Frequently asked questions