Following assisted reproduction treatment, the beta hCG test is often seen as one of the most eagerly awaited and, at the same time, most delicate moments of the process. Although the result indicates whether embryo implantation has occurred, interpreting a beta hCG test is not always as straightforward as simply getting a 'positive' or 'negative' result.
In many cases, the hormone level, the timing of the test and, above all, how the levels change in the days that follow is key to correctly assessing how the pregnancy is progressing.
What is beta hCG?
Beta hCG is the beta subunit of the human chorionic gonadotropin hormone. This hormone is produced by the embryo following its implantation in the endometrium, and its detection in blood or urine confirms pregnancy.
In in vitro fertilisation (IVF) treatments, this test is usually carried out between 9 and 14 days after embryo transfer, depending on the stage of development of the transferred embryo.
What beta hCG levels are considered positive or negative?
Although levels may vary slightly, it is generally considered that:
- A beta hCG level below 5 mIU/ml is usually considered negative.
- Levels above 25 mIU/ml are usually interpreted as positive.
- Results between 5 and 25 mIU/ml are considered indeterminate or inconclusive and usually require the test to be repeated after 48 hours.
What does a low beta hCG level mean?
A positive but low beta hCG level does not always mean that the pregnancy will go wrong. In some cases, it may simply be because implantation occurred later and the pregnancy is still very early.
However, low levels may also be associated with:
- Biochemical pregnancies.
- Slower-progressing pregnancies.
- Increased risk of early miscarriage.
- Ectopic pregnancy.
For this reason, when the initial beta hCG level is low or there is any doubt about its progression, the test is usually repeated after 48 hours.
Why is it important to repeat the beta hCG test?
The progression of the hormone is one of the most important factors in assessing whether the pregnancy is progressing properly.
During the first few weeks of pregnancy, beta-hCG levels tend to double approximately every 48–72 hours. A normal rise is usually a positive sign and in contrast, if levels rise very slowly, remain stable or fall, this may indicate that the pregnancy is not progressing as it should.
Can there be false positives or false negatives?
Although the blood beta hCG test is highly reliable, there are some situations that can cause confusion.
In fertility treatments, some medications used to trigger ovulation contain hCG. If the test is carried out too early, traces of this hormone may be detected, resulting in a false positive.
On the other hand, taking the test before the recommended time may result in a negative beta hCG result even if a pregnancy is present, simply because hormone levels are still too low to be detected.
Therefore, adhering to the timeframe indicated by the medical team is essential to obtain a reliable result and avoid misinterpretation.
When is pregnancy definitively confirmed?
A positive beta hCG indicates that embryo implantation has taken place, but it does not in itself confirm that the pregnancy is progressing.
Definitive confirmation is usually made via transvaginal ultrasound a few weeks later, when it is possible to visualise the gestational sac and check the progress of the pregnancy.
Until that point, changes in beta hCG levels help guide the prognosis and allow the medical team to monitor the pregnancy more accurately.
