Pregnancy Blood Test: Procedure, Accuracy and How Early To Do It

Pregnancy blood tests, also called the pregnancy serum tests, are done in a medical facility such as a laboratory to confirm if you are pregnant. They are not done at home.

They are very accurate more than the home pregnancy tests and can detect your pregnancy much before than the urine test.

Besides just telling you whether you are pregnant, the pregnancy blood test results also help to diagnose any pregnancy abnormalities such as a miscarriage or an ectopic pregnancy.

This is a very handy tool for mothers-to-be, who are very anxious to know about their pregnancy status for the simple reason that these tests are very accurate and you can perform them as early as one week after conception or ovulation day.

How is it done? Procedure

A technician draws the blood sample with a syringe from the vein on the front side of the elbow or he may draw it from the back of the hand.  He then uses the sample to conduct the test.

He ties a tourniquet above the elbow to make it easy to draw blood from the vein.

The test basically determines the presence of the Human Gonadotropin Hormone (hCG) in the blood. This hormone is also called the pregnancy hormone because it is produced during pregnancy by the placental cells.

It is the placenta that nourishes the fertilized egg and binds it to the wall of the uterus.

How accurate are pregnancy blood tests?

Though the home pregnancy test gives a fairly accurate result, the pregnancy blood test is more accurate and has an advantage over the home test as far as accuracy is concerned.

The blood test can also detect pregnancy at an earlier date than the home or urine pregnancy test. And besides, more information about the pregnancy (described below) can be gathered via this blood test.

The blood pregnancy test requires only 5 units of human chorionic gonadotropin hormone (hCG) in blood to show a positive result as against the home pregnancy test, which requires 25 to 100 units to be present in the urine. This indicates a very sensitivity.

The pregnancy blood test is more accurate at 99% than a home pregnancy test, which boasts of 97% accuracy. The chances of a wrong result with the blood test are one in hundred.

False negative result

You are pregnant and yet the pregnancy blood test shows a negative result. Looking at its accuracy rate, this is likely due to two reasons:

1.     Human error in the laboratory

2.    You have tested too early in your pregnancy. Recommended day of testing is about a week after the ovulation day.

If a negative result does show and you feel you are pregnant, test yourself again after 48 to 72 hours to see how the hCG hormone levels are rising.

False positive result

On the other hand, you may get a positive false result even if you are not pregnant. This can happen;

1.     Due to a defect in the blood test or human error

2.   Phantom hCG is a positive pregnancy test without being pregnant.
3.    A chemical pregnancy is a condition in which the blood and the urine tests show a positive report but the pregnancy does not develop and there is a very early miscarriage or spontaneous abortion.

4.   Certain drugs can give a false positive pregnancy test. examples include:

  • Methadone used as pain reliever and in drug addiction detoxification,
  • Chlordiazepoxide used to treat anxiety and acute alcohol withdrawal,
  • Promethazine, an antihistamine used to treat allergy symptoms, nausea and vomiting after surgery and to prevent motion sickness.

5.    Islet cell tumor of the pancreas, though rare, can cause a false positive response to the test.

How early can the blood test detect pregnancy?

Blood pregnancy tests are more sensitive and can detect pregnancy earlier than the home pregnancy urine test. They can tell you are pregnant even when hCG concentration in blood is 5 to 25 milli-International units per milliliter of hCG in blood.

According to a study published by “Sterility and Fertility” in 1982 by Dr E. A. Lenton, about 5ml I.U. per ml of hCG can be found at the time of fertilization of the egg by the sperm and about 25 ml I.U. per ml of hCG can be found when the fertilized egg gets implanted on to the uterine wall.

But, blood pregnancy tests can give a more accurate result about a week after the ovulation or conception day, that is even before you would know whether you will miss your period or not.

This helps to satisfy the anxiety of an over anxious mom–to–be. Accuracy of this test is rated at 99%.

However, If you take the pregnancy blood test too early, you could;d end up with a false negative result. To ensure accuracy, follow the instructions on the manual carefully.

How does the blood pregnancy test work?

The pregnancy blood test is done by testing the blood for the presence of Human Chronic Gonadotropin (hCG), also called the pregnancy hormone, which is a hormone produced in the body when a woman becomes pregnant. HCG is produced by the embryo in the initial stages and later by the placenta.

The concentration of hCG in blood varies from woman to woman and is low very early on after conception.This makes it difficult to be detected by low sensitivity tests.

There are two types pregnancy blood tests:

Qualitative blood pregnancy test or hcg blood test

The qualitative blood test simply tests the presence of hCG in blood. This test will simply tell you if you are pregnant or not. It is a sensitive test and can answer your question as early as 6 to 8 days after your ovulation date.

Quantitative blood pregnancy test or Beta hCG test

The quantitative blood test test gives more details about your hCG blood levels and can help measure the exact amount of hCG in blood. These numbers obtained during this pregnancy test are significant to monitor the age and progress of the pregnancy.

It helps in finding how old the pregnancy is and also to detect any pregnancy-related problems you may have such as an ectopic pregnancy (a condition where pregnancy grows in the fallopian tube instead of the uterus) or to monitor falling hCG levels after a miscarriage or abortion.

At times, the hCG blood test is performed to determine pregnancy in the early stages before the woman is subjected to other potentially harmful treatments or tests such x-rays, which can harm the fetus..

Pregnancy blood test results interpretation

How does the quantitative pregnancy blood test help detect pregnancy problems?

It is important to understand that the hCG blood levels rise rapidly and continuously over the first trimester doubling every 48 to 72 hours, peaking somewhere between 8 and 11 weeks and then the levels plateau off or decline to level off for the rest of the pregnancy.

That is why to monitor proper progress of the pregnancy during the first trimester, the quantitative pregnancy blood test is done repeatedly during pregnancy to see whether the hCG levels are rising as they should.

If they aren’t, your pregnancy is in problem. A miscarriage or abortion can cause the hCG levels to fall instead of to rise.

According to ectopic.org.uk, a declining hCG result can also possibly indicate an ectopic pregnancy. An hCG level that is rising by less than 66% over 48 hours indicates the likelihood, not a certainty, of an ectopic pregnancy.

This early suspicion can help treat many an ectopic promptly and save the woman from its complications.

If it is found that the levels of hCG are higher than what they should be, then it could mean any of the following:

  • A wrong calculation of the dates
  • A molar pregnancy (A molar pregnancy is a noncancerous tumor that develops in the uterus instead of the fertilized implanted egg developing into a fetus).
  • Multiple pregnancy (twins or triplets)

Cost

Most insurance companies cover this cost, if you are insured. The cost of the pregnancy blood test varies from place to place and can range from $50 to $100. The consulting cost of your obgyn doctor will be separate.

Disadvantages of pregnancy blood test

  • Longer time to obtain results as compared to urine or home pregnancy test
  • More expensive
  • Has to be done in a laboratory – therefore consumes more of your time
  • Can occasionally give rise to minor complications such as infection or hematoma at the vein puncture site or excessive bleeding from the punctured vein.

Advantages

  • The blood test is more sensitive and can detect pregnancy a week or so after conception. However, if the test is negative, you should repeat it a day after you have missed the period.
  • The qualitative hCG blood test can measure the levels of hCG in blood. This can help to track any problems in pregnancy such as a miscarriage or an ectopic pregnancy as described above.

How long does the pregnancy blood test result take?

Though the pregnancy blood test procedure takes only a few hours to do, the result of your pregnancy blood test should be available within one to three days depending on how busy the laboratory is.

 

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