2021-09-09 13:23:30
Something tells you that you might be pregnant? Two choices available to you to confirm the diagnosis of pregnancy: a urine test bought in pharmacies or supermarkets, to do at home, or a simpleblood test made in a medical analysis laboratory.
What is a pregnancy blood test or beta-HCG?
Both the urine test and the blood test work on the same principle: detect the presence of the beta-HCG hormone in blood or urine.
The HCG hormone, or chorionic gonadotropic hormone, is a hormone secreted by the future placenta, which at this stage is called the ‘trophoblast’.
“When this future placenta enters the uterine lining and connects to the blood vessels, the hormone beta-HCG can then circulate in the blood of the future mother “, explains Dr. Multon, gynecologist and obstetrician. The level of this hormone increases steadily and gradually during the first 8 weeks of pregnancy. It is at this moment that a blood test allows a clear result of the situation.
Is a beta-HCG blood test more reliable than a urine test?
Question reliability, there is nothing to worry regarding: the two tests offer a result that is now reliable on which to rely.
In a woman who knows herself well, who lives a regular cycle, and who has a late period, there is no possible ambiguity: if the urine test is positive, there is no need to double that with a blood test, says the doctor.
On the other hand, opting for a maternal blood sample can be recommended depending on the context and the situation of the patient.
When should you take a blood test to find out if you are pregnant?
While the urine pregnancy test is quite sufficient in many cases to detect pregnancy, the blood test has the advantage of being slightly more sensitive to hormones and more precisely quantify its level in the blood. Depending on the context and the history of the woman who is questioning, the blood test can be a more precise medical tool:
When there is a medical history
A woman who has had one or more ectopic pregnancies (EUG), a miscarriageor who is taking treatment to get pregnant will be directed to a blood test,
For a matter of trust
Dr. Multon agrees, “there are still a lot of patients who have need to be reassured regarding their new pregnancy and this blood test seems more reliable to them, especially when they fear a false negative or positive, for example, on a urine test”. Indeed, the result is written there in black on white.
To have access to a refunded exam
The advantage also of the blood test is that it remains, unlike the urine test, a medical examination reimbursed by social security. In case of doubt, it is therefore quite possible to have a blood test quickly prescribed, reimbursed, an asset for the patient.
When should a pregnancy blood test be taken?
No need to rush to a laboratory the day following unprotected sex. “The beta-HCG hormone becomes detectable only when placenta begins to attach to the uterine wall a few days following fertilization. The first cell must first divide thousands of times and head for the uterus,” explains the doctor.
In concrete terms, this means that we have to wait the necessary period of 12 to 14 days between ovulation and implantation in case of pregnancy to analyze the blood of the (possibly) pregnant woman. On the other hand, it also means that the HCG hormone is detectable from the first day of delay of the expected period.
How to read a pregnancy blood test?
Different laboratories have different techniques for quantify the HCG hormone in the blood test. Nevertheless, they all agree on the threshold that determines a pregnancy: the hormone is counted in unit per liter (IU/L), and the threshold is set at 5 IU/L.
- Below this threshold for Dr. Multon, there is a small uncertainty;
- At 5 units, the test is positive and confirms pregnancy;
- A beta-HCG level that doubles every 48 hours indicates the good progress of the beginning of the pregnancy.
Are there false positives or false negatives with a blood test?
The facts are rare but can exist. “False positives can occur in extremely rare cases and fortunately, because these are ovarian tumors or tumors of the placenta which would also secrete HCG hormones. Otherwise, no, false positives do not exist,” says the practitioner. As for the false negatives, if there is indeed a pregnancy which is confirmed later, they are only the sign that the blood sample was taken too soon, when the hormone threshold was not yet detectable.
In which cases can the blood test be repeated?
In some special cases at the start of pregnancy, the beta-HCG assay may require more than one blood test. “This is what we do when the rate is still too low, when we are not sure of a pregnancy. If the sample is taken too early in the first days of implantation, a second analysis may of course be necessary”, explains Dr. Multon.
When in doubt regarding the correct installation
The blood test and its measurement of the HCG level are also repeated when you want ensure proper implantation of the embryo and an early pregnancy that is taking its course. “The growth of the pregnancy hormone is quite linear in the early days of embryonic development, when implantation is going well. His rate will double every 48 hours “says the gynecologist. “However, if a growth is not of this order, one can suspect a pregnancy which stops, and therefore a future miscarriage, or an ectopic pregnancy ».
In this case, a new blood test will be done every 48 hoursuntil the certainty of the implantation of the pregnancy, which will be perceived on the ultrasound when the HCG hormone threshold reaches 1,000 IU/L.
Pregnancy blood test: other information you need to know
Prescription, price, results: here is what you need to know before taking a blood test to find out if you are pregnant.
Do I need a prescription?
No, the prescription is not not mandatory for a beta-HCG diagnostic test. Your laboratory can carry out this detection of pregnancy hormones by blood test on your simple request. Nevertheless, your practitioner, doctor or gynecologist can just as easily prescribe this examination, which will then be 100% supported by the Health Insurance Fund.
How much does a pregnancy blood test cost?
If you do not go through the prescription stage, possible on simple request to your doctor, the biological procedure will cost you around 17 euros without refund.
Should I be fasting or not for the sample?
No, it is not useful to be on an empty stomach for this blood test, it absolutely does not change the result and does not modify the level of beta-HCG detected. For a quick result, it is better to come at the beginning of the day, but the test is possible at any time of the day.
Result of the pregnancy blood test: in how long?
The HCG assay is a relatively quick act. “Depending on its workload, a laboratory is able to provide you with this result between 1 and 3 hours, especially if you come for a sample in the morning,” says the doctor. In hospitals, when the emergency is a data to be taken in addition (for example in the suspicion of an ectopic pregnancy) the results are available in one hour.
Positive pregnancy test: what to do when you find out you are pregnant?
For the doctor, once the result is confirmed, it is contact the person who will monitor the pregnancy to support it, whether you decide to pursue it or not. In the case of a classic and desired pregnancy, your doctor or gynecologist will plan your first consultation. In the case of a less obvious pregnancy (irregular periods, difficulty getting pregnant, history), an early ultrasound may be considered to obtain a precise dating and to ensure the correct location of the pregnancy.
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