Pregnancy Blood Test

A pregnancy blood test is a routine part of everyone’s prenatal healthcare, however there are other types of tests done during pregnancy that may apply to you personally, however, trying to understand all the different terms such as screening, diagnostic, genetic and congenital can all become a little overwhelming.


Blood Screening Test

Antenatal testing (or prenatal) is a very complex area that does not always offer the assurance needed for many women. This section is to give you a better understanding of the screening process used with a pregnancy blood test, which tests will be offered to you in addition to your healthcare, why they are taken, when and what they involve.

See also: Antenatal Notes and Booking Visit

First of all there are 2 areas of antenatal testing and 2 different medical categories that are investigated:

Blood Screening Test – This usually takes the form of a pregnancy blood test and is used only for screening purposes to see if you are at risk of having a baby with a medical condition or not. If a first trimester screening test determines that you are at risk then this does not necessarily mean that there is anything wrong with your baby at this stage. It simply means that you are deemed high risk therefore closer monitoring and further diagnostic testing will be offered or undertaken to determine if there is actually anything wrong or not.

Diagnostic Test – This type of test gives you actual confirmation that your baby does, or does not, have a condition such as Spina Bifida or Down Syndrome and comes in the form of an amniocentesis test or chronionic villus sampling, for example.

Genetic Condition – Conditions such as Down Syndrome, Edward’s Syndrome or Turner’s Syndrome are the result of faulty genetic information in either the sperm or the egg that fused together, therefore, these conditions are unavoidable from the start as they are already built into the baby’s genetic blueprint and, unfortunately, they cannot be corrected.

Congenital Condition – This type of medical condition is the result of something going wrong after a healthy conception took place. These congenital problems can be caused by toxins, poor diet and viral or bacterial infections effecting the womb. Conditions such as Cystic Fibrosis, Spina Bifida or Fetal Alcohol Syndrome would be considered as congenital disorders.

Prenatal Tests by Trimester

First Trimester

8-12 weeks:

  • pregnancy blood test (screening)

10-13 weeks:

  • nuchal translucency test (screening) – Assesses the amount of fluid behind the fetus’s neck, thus indentifying pregnancies that are at risk from Down Syndrome.
  • chorionic villus sampling – CVS (diagnostic) – Collects a sample of cell tissue or villi from the placenta to test for any genetic abnormalities. Not reliable at detecting congenital defects.

Second Trimester

16 weeks:

  • triple test (screening)
  • afp screening (screening)

16-20 weeks:

  • amniocentesis (diagnostic)- Tests the amniotic fluid for fetal chromosomal abnormalities. Sometimes carried out as early as 14 weeks. If results are needed earlier, then a ‘CVS’ (see above) could be considered instead.

18-20 weeks:

  • ‘cordocentesis’ also called ‘percutaneous umbilical cord blood sampling -PUBS (diagnostic) – This is useful when the results of an amniocentesis were inconclusive. It takes a sample of fetal blood direct from the main artery of the umbilical cord for testing

20 weeks:

  • ultrasound scan (screening and diagnostic) – This is a complete health check on your baby, looking for defects and taking measurements to ensure healthy growth and development.

Third Trimester

24-28 weeks:

  • glucose test (screening) – Looking for signs of (gestational diabetes)

32 weeks:

  • ultrasound scan (screening and diagnostic) – Checking the baby’s heartbeat and position

35-37 weeks:

  • Group B Streptococcus GBS (screening) – This determines if a vaginal bacterial infection is present before going into labor as this can cause life threatening infections with newborns. If the test is positive, you will be given intravenous (IV) antibiotics during labor.

40+ weeks:

  • non-stress test – Usually only performed if you have past your due date or suffer with gestational diabetes to check if the baby is suffering any fetal distress.
  • biophysical profile (BPP) – this is also a non-stress test, accompanied by an ultrasound and it is carried out if the non-stress test above delivered undesirable results.
  • contraction stress test (the oxytocin challenge test – OCT) – This test can be performed if the above 2 tests displayed potential fetal distress. This test determines how a fetus will manage labor as heavy contractions can lower fetal blood and oxygen supply. The doctor will then decide whether a C-section is required or not.

A pregnancy blood test, along with a urine sample and blood pressure analysis will be carried out routinely at every antenatal appointment.

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