Biochemical Pregnancy

What is a Biochemical Pregnancy?

If a woman is not pregnant and she has a blood pregnancy test, the result would be negative, as there is no pregnancy hormone (beta hcg) circulating in her blood stream.  Now assume that she becomes pregnant by whatever means (naturally or following fertility treatment), the same blood pregnancy test would be positive as there is now beta hcg circulating in the blood stream.  These levels are initially quite low but as the pregnancy becomes more established, the levels will rise at relatively predictable rates.  For example, in a normal pregnancy, levels rise by roughly doubling every 48 – 72 hours.  In a multiple pregnancy, the levels usually rise faster than this.

In these early stages of the pregnancy, the woman does not look pregnant.  Further, if an ultrasound exam was performed, it would not show any evidence of pregnancy.  This period is called the BIOCHEMICAL PHASE because in reality, the only way we know the person is pregnant, is by doing biochemical blood or urine tests.  Eventually, the levels of beta hcg would rise to a level (usually > 2000 mIU/ml), where it would be possible to see evidence of the pregnancy on ultrasound. Initially there would not be a fetal heart beat present but eventually the fetal heart will be seen and eventually heard by Doppler.  Also, if there is a multiple pregnancy, one would be able to see the number of gestational sacs within the uterus.  Later still, the abdomen will start to bulge and the person can easily be seen to be pregnant.  The phase of the pregnancy which follows the BIOCHEMICAL PHASE, is referred to as theCLINICAL PHASE and the medical term for this is a CLINICAL PREGNANCY.

Therefore, the BIOCHEMICAL PHASE refers to that stage of pregnancy from the time of conception or implantation, until there is evidence by ultrasound or Doppler testing and ultimately by physical inspection of the mother, that a CLINICAL PREGNANCY is present.    If for any reason the pregnancy fails to progress, we say the person had a BIOCHEMICAL PREGNANCY.

Is a Biochemical Pregnancy a real Pregnancy?

A biochemical pregnancy is indeed a real pregnancy.  It implies that an embryo has implanted and secretion of pregnancy hormone ( beta hcg) has taken place and was able to be detected in the mother’s blood stream.  With extremely rare exceptions, PREGNANCY IS THE ONLY TIME beta hcg is secreted into the blood stream.

What are the medical implications of a Biochemical Pregnancy?

For patients undergoing medical treatments for fertility, biochemical pregnancies have important medical implications.  As discussed above, this event means that an egg became fertilized and early implantation took place.  Unfortunately, we often do not know where the implantation occurred – e.g. in the uterus or the fallopian tube ( ectopic pregnancy) .  For example if a person has a positive pregnancy test, and then after a few positive tests, the levels start to drop, it could mean that the implantation took place in the fallopian tube and then it spontaneously aborted and the person had an early tubal abortion.

Other possible reasons for biochemical pregnancies, could be immunological implantation rejection.  This becomes especially important if biochemical pregnancies occur repeatedly. It may imply that the mother’s immune system recognized the pregnancy as “foreign tissue” and mounted a Rejection Reaction to the pregnancy, before it was able to become fully established as a clinical pregnancy.   This is an extremely complex medical situation and beyond the scope of this piece.  Other possible explanations for biochemical pregnancies include uterine fibroids, polyps or adhesions, which may negatively impact on the implantation of the early pregnancy.  Also, past pelvic infection can have disruptive effects on early pregnancies and result in a biochemical pregnancy.

One of the reasons biochemical pregnancies are so common in patients undergoing fertility treatments, relates to the fact that these patients are monitored so closely after any fertility interventions.  In reality it has been estimated that biochemical pregnancies occur in up to 60+% of all pregnancies in humans.  However, most people are not being monitored closely with blood tests.  Usually someone would simply experience a delayed or slightly heavier than normal menstrual period.  In reality they may have initiated a pregnancy which was not destined to progress.  It is quite fortunate that nature has powerful, in-built “clearing mechanisms” to ensure that not every pregnancy will continue, as we understand from research that the majority of these pregnancies are chromosomally abnormal.

In a sense, a biochemical pregnancy is frequently a retrospective diagnosis.  For example, if a person conceives following fertility treatment and we perform a blood test and it is positive, we do not know at that time that the person is going to have a biochemical pregnancy.  All we know at that time is that she is in the biochemical phase of what we hope will progress and ultimately become a clinical pregnancy.  If she goes on to lose that pregnancy before it has a chance to progress to a clinical pregnancy, we can say in retrospect that she had a biochemical pregnancy.

Rev 04/12