What does it mean if the pregnancy test shows a correct positive result, but the ultrasound examination cannot confirm the pregnancy? Well, this is called a biochemical pregnancy.

A biochemical pregnancy means that it is a pregnancy that stops growing and resolves before it becomes large enough to see it in an ultrasound examination. Not long after fertilization and implantation, the pregnancy stops developing – usually due to a severe chromosomal abnormality within the pregnancy. The term“biochemical” means that the only evidence that the pregnancy existed was the positive pregnancy test itself.

So, sometimes it can happen that even though the result of a pregnancy test was a real positive, it is not possible to confirm the pregnancy by ultrasound. This is referred to as a biochemical or chemical pregnancy and means that although the fertilised egg has been embedded and the placenta has formed, which has led to the positive detection of hCG (human chorionic gonadotropin), the development of the embryo has not continued and the previously embedded egg has detached itself from the uterine wall. Biochemical pregnancies are the earliest form of miscarriage.

The vast majority of miscarriages are happening due to one or more chromosomal abnormalities. This may be the case when an abnormal egg is fertilized by a “normal” sperm, when an abnormal sperm fertilizes a “normal” egg. It may also occur when a mistake happens during cell division following normal fertilization. This typically results in embryos that do not have the normal number of 46 chromosomes. Embryos that do not have this number of chromosomes almost always miscarry spontaneously.

In the case of such a biochemical pregnancy, a pregnancy can be detected early by biochemical analytical testing, but ultrasound cannot detect it at a later stage.

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