When is a blood test for beta-hCG necessary?

By Dr Valentina Pontello Ob/Gyn Specialist

A laboratory blood test for beta-hCG is necessary when the doctor needs to check the quantitative level of the hormone. The value of beta-hCG is related to the gestational age and grows exponentially in the first weeks of pregnancy (when it doubles every 48 hours), while from the 6th-7th week of gestation a 30% increase is sufficient to indicate a probable vital pregnancy. One blood test positive for beta-hCG tells us that there is a pregnancy, but to have some information about viability, two blood tests 48 hours apart are needed. The blood level of beta-hCG (high or low) does not give indication on miscarriage risk before the third month of pregnancy, which is the period when the risk is higher. In general, you will not need to take a beta-hCG blood test at the laboratory, unless it is prescribed by the doctor in particular cases (genital bleedings, IVF, previous miscarriages, or extrauterine pregnancies). On the contrary, it may be a cause for anxiety when the levels do not increase sufficiently. Transvaginal ultrasound is a very reliable method to assess a viable pregnancy.