More than 300,000 babies are born in Australia each year, but do you know just what you’re in for as an expectant mum?

Trimester 1

6 – 8 weeks

On the first GP visit to confirm a pregnancy, a woman will be offered several blood tests. A full blood examination will check for possible iron deficiency and thalassaemia risk. A ferritin level may be included and is more sensitive than the full blood alone to determine reduced iron stores.

A blood group will determine not just the ABO group but more importantly identify individuals with a Rhesus negative blood type who should be offered prophylactic therapy during pregnancy to prevent one of the causes of pregnancy loss and new-born jaundice (haemolytic disease of the foetus and new-born).

Women are also screened for infectious disease exposure or immunity including HIV, and Hepatitis B and C which can put babies at risk of future liver disease if not treated. Testing for antibodies to rubella and chicken pox is conducted as exposure to these viruses during pregnancy can cause birth defects if a woman is not immune.

A woman can also talk to her doctor about whether testing for chlamydia, syphilis, thyroid disease and vitamin D is necessary.

After 10 weeks

Combined first trimester screening usually takes place between the 10th and 14th week of the pregnancy to determine the chance of the pregnancy being affected by certain chromosomal abnormalities such as Down syndrome (trisomy 21), Edwards syndrome (trisomy 18) or Patau syndrome (trisomy 13).

This combines information obtained by an ultrasound and blood tests.  The ultrasound is performed between the 11th and 13th weeks, predominantly to assess nuchal translucency, the thickness of the fold at the back of the baby’s neck.

Together with the maternal age, weight, gestation and maternal blood test results (free beta-human chorionic gonadotrophin, pregnancy-associated plasma protein-A) obtained between the 9th and 13th weeks of the pregnancy, the chance of a baby affected by these abnormalities is determined.

Further blood tests are available where parents have close blood relatives carrying other genetic disorders.

Trimester 2

15 – 17 weeks 

Multiple Marker Screening or Maternal Serum Screening involves a blood test that looks for both Down syndrome, Edwards syndrome and neural tube defects such as spina bifida and anencephaly, in which the skull does not form properly.

The screen looks for four chemicals in the blood, alpha-feto protein, unconjugated estriol, free beta hCG and dimeric inhibin A.

Again, these results are combined with the nuchal translucency results and other information about the pregnancy to assess the chance of a fetus having abnormalities.  All tests have limitations and may not be diagnostic alone.

Non-invasive prenatal testing

Non-invasive prenatal testing (NIPT) can offer better accuracy in detecting chromosomal abnormalities. This tests fetal DNA that is released normally into the mother’s blood. 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 so carry a risk of miscarriage, making NIPT a potentially safer option. Amniocentesis tests fetal cells in the amniotic fluid and CVS tests cells taken directly from the placenta.

Trimester 3

24 – 28 weeks

Between 3-8% of women get gestational diabetes between the 24th and 28th week of pregnancy, sometimes earlier. It usually goes away after the baby is born. A glucose tolerance test uses three blood samples: the first sample is taken before a standardised glucose drink is consumed, the second sample one hour after and the third sample two hours after the glucose load.

A pathology laboratory compares results from all samples to see if they indicate gestational diabetes. The condition can be managed with lifestyle changes, monitoring blood glucose levels and sometimes medication.

The full blood examination is usually repeated towards the end of the second trimester, looking for the development of iron deficiency anaemia, which is extremely high in pregnancy, as well as to check the platelet count which may sometimes fall as a result of pregnancy complications.

Rhesus negative women will also have their antibody status checked prior to receiving their first dose of anti-D at 28 weeks.

Other tests

Pregnant women may also be tested for Group B Streptococci (GBS) bacteria via a vaginal or anorectal swab at 35-37 weeks. These bacteria occur naturally in some women and are usually not harmful however, if passed on to a newborn in the birth canal, the baby can become very ill. Pregnant women carrying these bacteria can be offered antibiotic treatment during labour as a measure to help protect a baby from becoming infected.

Women may also be offered pathology tests if they fall ill 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.

How did your prenatal testing go? Share your thoughts in the comments.