South African Society for Ultrasound
in Obstetrics and Gynaecology

For Patients

Prenatal tests

Your clinician (Obstetrician, General Practitioner or Midwife) will request some tests to check that all is well with your pregnancy. Some are optional and may depend on whether you can afford them or not.

The tests include the following:

Routine tests to check your health and risks to the pregnancy
  • Your A, B, O and Rhesus blood group and antibodies (to see if your baby is at risk of anaemia or jaundice because your blood group differs from the baby’s father’s);
  • Your haemoglobin level (to check if you are anaemic);
  • Antibodies against Rubella (German measles), HIV, hepatitis B and syphilis (to see if your baby is at risk of sustaining an infection before birth);
  • Your blood glucose level (in some cases) (to check if you have diabetes, which might be underlying or brought on by the pregnancy);
  • Your blood pressure (to check if you have hypertension, which might be underlying or brought on by the pregnancy as in a condition called pre-eclampsia);
  • Your urine (to check for a bladder infection, or for protein in your urine (which might also indicate pre-eclampsia or underlying kidney disease);
  • A swab (in some cases) to check whether a bacterium called group B streptococcus is present in your vagina (this could cause a serious infection in the baby if born vaginally);
  • A basic ultrasound scan to determine exactly how far you are pregnant, whether the baby is in the uterus (womb) and alive, whether there are twins or not, to check the amniotic fluid volume around the baby and the position of the placenta (afterbirth).

Routine tests to check whether your baby is at increased risk for physical or mental problems.

The vast majority of babies develop normally but every pregnancy carries a small risk that the fetus (unborn baby, still in the mother’s womb) is not developing normally. It is important to realize that no test or combination of tests is fool-proof and that one can ever guarantee you will give birth to a baby without any abnormality.

The following risk factors indicate that your chance of carrying a fetus with an abnormality is higher than average and it is important that you inform your doctor of any of the following:
Yes or No
I am 35 years old or more
I have epilepsy (fits, seizures, convulsions) and take medication for it
I have diabetes
I take medication for a chronic condition
I have used over-the-counter medication/herbal remedies/traditional medicine during this pregnancy
I took medication for a chronic condition within 3 months before falling pregnant
I did not take vitamin supplements before I fell pregnant
I have had a previous pregnancy with an abnormal fetus
I have lost a previous pregnancy at a late stage
I have had more than 1 previous miscarriage
I or my partner or one of our family members was born with an abnormality
I or my partner or one of our family members suffers from mental impairment
I or my partner or one of our family members had a termination (abortion) for an abnormal pregnancy
There is a genetic (inherited, familial) condition in my or my partner’s family
I have smoked during this pregnancy
I have used alcohol during this pregnancy
I have used recreational drugs during this pregnancy (Marijuana, TIK, methamphetamine, heroin, cocaine etc…)

Available tests include prenatal screening tests and prenatal diagnostic tests. These tests are optional, but may provide valuable information for the management of the pregnancy.

Screening and diagnostic tests

Screening tests are tests that can be done on everyone who wants it, but they do not give a definitive answer about whether a condition (for example Down syndrome) is present or absent. They only give an indication of the likelihood of the condition being present, expressed either in numbers (risk of 1 in xxx) or as low, intermediate, or high risk. The majority (but not all) of affected individuals would have a “high risk” result on their screening test. The proportion of individuals with the abnormality who are identified by the test is called the sensitivity or detection rate. The proportion of normal individuals that received a “high risk” result is called the false positive rate. The abnormal fetuses that had a “low risk” result are missed by the screening test and called false negative results. Ideally, a screening test needs a high sensitivity (although it is never 100%) and low false positive rate (although it is never 0%).

Diagnostic tests on the other hand give a definitive answer about whether this condition is present or absent. Diagnostic tests have some features that make them unsuitable for use on a wide scale, such as risk or cost associated with the test or limited availability. The choice of a specific diagnostic test depends on the specific condition that one wants to detect or exclude. Options for diagnostic tests include ultrasound examinations by an expert (e.g. for physical defects in the fetal body parts) or invasive procedures where a needle is passed through the mother’s skin and into the womb to obtain samples (specimens) for genetic or infective testing (chorionic villus sampling to obtain a piece of placental tissue, amniocentesis to draw some of the fluid that surrounds the fetus, cordocentesis to draw blood from fetal blood vessels in the umbilical cord which is located outside the fetal body but connects the fetus to the afterbirth). All invasive tests carry a risk of miscarriage (approx. 1:200). More information regarding specific invasive tests can be provided by your obstetrician or genetic counsellor.

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