How accurate is a pregnancy test?

by Dimitrios Dovas on September 20, 2018


How accurate is a pregnancy test?

How reliable is the pregnancy test? 

Perhaps the most difficult part for a woman who has undergone IVF treatment is the waiting period from embryo transfer to the pregnancy test. 

Emotions are mixed, since on one hand there is the expectation of a positive result and on the other the fear of failure. 

It is logical for a woman to feel powerless to manage the situation as the days go tortuously late.

So, in many cases, it feels as an ideal solution to do a pregnancy test earlier to clarify the situation.

When should the pregnancy test be done? 

As a rule, the pregnancy test is performed 14 days after the day of the egg retrieval. 

This means that the testing day can’t be fixed based on the embryo transfer day. For example, if embryos are at the blastocyst stage, testing is done nine days after embryo transfer, but if the embryos are on Day 3 of their development the pregnancy test is performed 11 days following the embryo transfer. 

Things can become more complicated in fertility treatments with frozen embryos or in egg donation programs.

Generally, since most treatment cycles are artificial, pharmaceutically induced cycles, dates should not be confused with what would normally happen in a natural cycle. 

For this reason, it is necessary to follow the instructions of the IVF Center exactly as indicated, since the calculation is personalized for each woman.

Urine or blood test? 

In almost all cases, it is suggested that the test should be performed using a blood sample and there are many good reasons for this, the most important being the accuracy of the blood test. 

The concentrations of the pregnancy hormone (chorionic gonadotrophin, βHCG) circulating in the blood are at least two times higher compared to the concentrations in the urine. This means that in some cases the test may be positive, and it doesn’t not show up in the urine test. 

In addition, the blood test has the advantage of being quantitative as opposed to the urine test that is qualitative. This means that with the urine test we simply know if the result is positive or negative, while with the blood test we also know the levels of βHCG. 

This is very useful because usually following a positive result we tend to control again hormonal levels in about 48 hours, as they tend to double in most occasions in ongoing pregnancies. 

One should not forget that in cases of outdated or poorly conserved urine tests we may get a false negative result, meaning that a woman could be pregnant, but the result comes up as negative. 

Such a development can lead a woman to discontinue the medications due to the frustration of the negative result, but these medications are important to maintain pregnancy in the early stages.

When the blood test is considered positive? 

Generally, blood βHCG levels above 5-10 units (IU / Lt or mIU / mLt) are considered positive. There may be a small fluctuation in the results in between labs. Therefore, it is extremely important when repeat testing is performed to use the same lab where the first test was done for the results to be comparable.

Extra tip: Can the result be false positive?

In cases when the test is performed too early and chorionic gonadotropin has been used to mature the follicles for the oocyte retrieval, then the result may be positive while there is no pregnancy. Generally, however, the values become negative seven days after the HCG injection.

Dimitrios Dovas, MD, DFFP

Dimitrios is the Medical Director of Newlife Center of Reproductive Medicine, in Thessaloniki Greece and is also responsible for all international patients.
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