The pregnancy test, or pregnancy-specific hormone measurement, is the modern laboratory’s means of detecting or ruling out a pregnancy before being visible through imaging methods such as sonography or medical ultrasound. The great advance, later, was the development of easy-access home tests and with a price for a pregnancy test much lower than the test performed in the clinical laboratory. The fundamental advantage is that in our times the woman with suspected pregnancy can confirm it quickly and long before the product acquires significant dimensions or that a surgical diagnosis is delayed, potentially fatal, such as Ectopic Pregnancy .

The hormone is known as the human chorionic gonadotropin beta fraction or BhCG ??(in English abbreviations) and because it only occurs in pregnancy (and rarely in some cases of malignant ovarian tumors) is highly specific and sensitive to rule out or diagnose the pregnancy. This hormone has the fundamental role of stimulating the postovulatory ovary, specifically the yellow body (progesterone-producing structure), so that it continues to produce progesterone of ovarian origin so that pregnancy can be maintained until the progesterone of placental origin can do the rest of the pregnancy . The hCG of ovarian origin is necessary during the first 8 weeks of pregnancy, if in this period the ovary carrying the yellow body is removed, the pregnancy will be lost irremediably.

The discovery and development of sensitive measurement techniques has incredibly facilitated the gynecological-obstetric practice and saved countless lives.

Origin, detection and measurement of BhCG

HCG is a protein hormone produced by the placenta and begins to release into the mother’s bloodstream after implantation of the fertilized egg (7 days after ovulation / fertilization of the ovum) and therefore 7 days before The lack of the expected period is noted. In short, you can know the pregnancy before there is menstrual delay

HCG has many forms and subunits but the most specific to detect pregnancy is the Beta Sub-unit, so, the request that we usually make to the laboratory is written as follows: beta-hCG or BhCG. This protein has 145 amino acids and can be detected in urine and blood, qualitative measurements can be made (it only detects the presence of the hormone but does not measure its values) or quantitative (the concentrations of the hormone in maternal plasma are detected and measured) , let’s see:

Qualitative Measurements of BhCG

They only indicate that there is a pregnancy without indicating your time, it is the most used test. It can be done in urine (more frequent) or plasma / serum (less frequent, more expensive but more sensitive)

Although they can be done in urine (home or laboratory) and blood (laboratory), these tests are typically done with the urine of the expectant mother, and almost all devices for qualitative measurements can be obtained in pharmacies, for home use. It is one of the most popular tests in the world and practically all women know its existence. It allows you to practice the test in the comfort and privacy of the home and at a lower cost than the test performed in the laboratory. It is suggested to use the urine in the morning to favor the detection of the hormone in the concentrated urine during the night.

Urine detection level: the test is expected to be positive with values ??of 10 to 100 mIU / ml

Serum detection level: the test is expected to be positive with values ??from 5 mIU / ml

Biochemical pregnancy: A sensitive pregnancy test can be positive during the time of implantation, 1 week before the date of menstruation arrival. At this time and for a couple of weeks more there will be no evidence of pregnancy other than that manifested by the pregnancy test; This is known as biochemical pregnancy.

Quantitative measurements of BhCG : indicate the approximate time of pregnancy and provide information on the time from which an intrauterine pregnancy should be visible by high resolution transvaginal ultrasound.

This test is performed exclusively on blood (plasma) and allows to obtain a numerical value of the concentration of the hormone in the maternal blood. It is not a routine test since the qualitative detection of BhCG ??is enough to recognize what we are looking for, a pregnancy.

Detection level: the test is expected to be positive with values ??of 5 mIU / ml and above. It is much better and more consistent than the urine test; In addition, it allows us to know the approximate time of pregnancy (although this is not very efficient to say, because of the wide variability of the range of values ??for the same week).

Uses of Quantitative BhCG

BhCG discriminating zone: the quantitative measurement allows us to establish the cut-off point from which we should show an intrauterine pregnancy: from 2000 mUI / mL we must observe a gestational sac, and even when we do not see anything inside it there is actually an embryo smaller than 1 mm in length invisible by current imaging methods.

Discard an Ectopic Pregnancy (EE): in the presence of a positive qualitative pregnancy test without evidence of intrauterine pregnancy, 2 or 3 quantitative measurements of BhCG ??are performed until reaching the cut-off point of 2000 mUI / mL, at which point the coat. If from this point we do not show a gestational sac we can consider that there is an EE.

Molar pregnancy: quantitative measurements allow the diagnosis of a Molar Pregnancy (BhCG levels are abnormally high) and attest to the decrease in their levels after treatment.