So many questions and worries during pregnancy - pathology has the answers

Blood tests during pregnancy – what to expect when you’re expecting

During pregnancy, it is common for women to experience a range of emotions and expectant mothers may feel overwhelmed by the many areas of antenatal care recommended.

Some aspects of your antenatal care involve medical tests to monitor the health of you and your baby. The following guide outlines the different tests available throughout each trimester, and the purpose of each test. Of course, every test is optional.

Trimester 1

At 6-8 weeks’ pregnancy
When you first visit your GP to confirm your pregnancy, you may be offered screening blood tests to check for a number of conditions. A full blood examination (FBE) and ferritin test will determine whether you have enough haemoglobin in your red blood cells and check your iron stores, to make sure you’re not at risk of anaemia, which can make you tired and weak. In addition, you’ll be screened for HIV and Hepatitis B, which can put your baby at risk of future liver disease if it’s not treated. Finally, you’ll be screened for antibodies to rubella (German measles) and chicken pox; exposure to these viruses during pregnancy can cause birth defects if you aren’t already immune to them. You can also talk to your doctor about whether you need testing for Hepatitis C, chlamydia, syphilis and vitamin D levels.

At 10 weeks’ pregnancy
You will be offered the nuchal translucency test at 10 weeks in combination with your 12-week scan, which can determine your risk of carrying a baby with certain chromosomal abnormalities.

This test is performed using ultrasound, it can indicate the likelihood of abnormalities but cannot accurately diagnose a fetus with a chromosomal condition such as Down syndrome, Edwards syndrome and Patau syndrome. Additional blood tests are also available for expectant parents with close blood relatives who carry other genetic disorders.

Trimester 2

Between 15 and 17 weeks of pregnancy
Multiple Marker Screening or Maternal Serum Screening involves a blood test that looks for both Down syndrome and neural tube defects such as spina bifida and anencephaly, in which the skull does not form properly. The tests look for four chemicals in the blood alpha-feto protein, unconjugated estriol, free beta hCG and dimeric inhibin A.

These results are combined with the results from the nuchal translucency test as well as other information about the pregnancy to assess the risk of a fetus having abnormalities.

Non-invasive prenatal testing

Non-invasive prenatal testing (NIPT) can offer better accuracy in detecting chromosomal abnormalities. This is a blood test that tests fetal DNA in the mother’s blood so can detect abnormalities in the baby’s DNA. Testing is recommended between 11 and 16 weeks and may be carried out after a woman has had the nuchal translucency test or following the results of other blood tests.

Tests such as amniocentesis or chorionic villus sampling (CVS) are also available. These are more invasive tests; amniocentesis tests amniotic fluid and CVS tests cells from the placenta. Because of their invasive nature these tests carry a risk of miscarriage making NIPT a safer option.

Trimester 3
Between 24 – 28 weeks
Between three and eight per cent of women will get gestational diabetes between the 24th and the 28th week of pregnancy, sometimes earlier. It usually goes away after the baby is born. A blood glucose test screens for gestational diabetes by checking blood sugar levels before and after you consume a sugary drink. After the first blood sample is taken, you have a drink that contains glucose. One or two hours after you have the drink another blood sample is taken.

A pathology laboratory will compare results from both samples and if blood sugar levels are high in the second sample this may indicate gestational diabetes. The condition can be managed with healthy eating, physical activity, monitoring your blood glucose levels and sometimes medication.

Other tests

Women may also be offered pathology tests should they experience symptoms of illness while pregnant or if they are in a high-risk group – particularly during the early stages of pregnancy. Certain conditions can affect the unborn baby such as cytomegalovirus (CMV), toxoplasmosis and herpes simplex virus (HSV) and pathology can diagnose these conditions so that steps can be taken to protect mother and baby.