What is a biochemical pregnancy?

Man comforting his wife about biochemical pregnancy

Waiting for the pregnancy test after assisted conception is in some ways the most difficult period of time. Even when the pregnancy test is positive pregnancy, the potential outcome is not always positive. Of course, one always hopes for a healthy pregnancy resulting in a live birth. On occasion, however, the joy of that first test can be followed by the disappointing news of a miscarriage or biochemical pregnancy.

What is a biochemical pregnancy?

Biochemical pregnancy is defined as the absence of an identifiable pregnancy on ultrasound examination despite a positive urine or serum HCG pregnancy test. The transient rise in β-hCG – the hormone that heralds a pregnancy –  is what characterizes a biochemical pregnancy and differentiates it from the much desired clinical pregnancy. Specifically, a low peak in β-hCG (< 100 mIU/mL) is usually followed by a rapid decline. As far as biochemical pregnancy is concerned, its exact cause is unknown and there are no definite predisposing factors to be remedied in subsequent cycles.

How common are biochemical pregnancies?

In spontaneous conception, biochemical pregnancies are thought to be fairly common, involving as many as half of all pregnancies. An accurate number is, however, hard to determine because most women who experience a biochemical pregnancy never even realize they are pregnant unless they are trying to conceive and are testing regularly and early. Many biochemical pregnancies are discovered today that would otherwise have gone undetected due to the ultra-sensitive pregnancy tests on the market, which make it easier to get a positive result as many as 3 or 4 days before a woman’s period is due. Additionally, it has been established that as many as 25% of pregnancies fail even before the woman has any subjective indication that she is pregnant, that is, before she misses her menstrual period or has symptoms of pregnancy.

What causes a biochemical pregnancy?

Several attributable factors have been proposed but the exact relationship is unknown. These factors include:

Endometrial thickness and pattern:
Biochemical pregnancies are related to endometrial thickness and pattern, but are unrelated to maternal age or previous pregnancy loss. Neither biochemical pregnancy nor clinical spontaneous miscarriage is related to estradiol or luteinizing hormone (LH) levels on the day of hCG administration or LH surge. In other words checking hormone levels before conception can’t predict which pregnancies will be healthy and which will go on to unfortunately miscarry.

It is becoming clearer that the genetic make-up of the oocyte (egg) is pivotal to early embryo development. Recent hypotheses point to the presence of two distinct mechanisms of early embryo loss. The first is nondisjunction (absence of segregation) of chromosomes at the time of cell division and the second is cytoplasmic and energy supply incompetence in the early embryo. Meaning that the abnormal genetic material may come about in the egg or in the sperm even before conception or after they fuse to create an embryo in the very first days after conception.

What about Stress?
Day-to-day stress, intense exercise and lifting heavy objects are not considered by scientific evidence as causes of miscarriages. The only result of these persistent fallacies is a lot of unnecessary guilt and suffering for women today.

Clearly, to the IVF patient, the diagnosis of a biochemical pregnancy represents a severe disappointment. However its occurrence provides clear evidence that at least one embryo reached the advanced preimplantation phase of development (the blastocyst stage), went on to “hatch” and attempted to implant. As such, a biochemical pregnancy can often be regarded as being a “dark cloud that has a silver lining” because it offers the hope of a successful clinical pregnancy in the future.

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