Invasive tests such as Amniocentesis offer additional information on your baby, but come with a risk factor each mother will have to assess for herself.

These tests detect genetic conditions and diseases by checking the number and structure of your baby’s chromosomes for abnormalities. By extracting genes from the placenta, the umbilical chord or the amniotic fluid, a detailed picture of individual chromosomes or a 'karyotype' can be made.

All invasive tests slightly increase the risk of miscarriage and for this reason some women choose not to have them done.

Chorionic Villus Sampling (CVS)
The placenta is made out of chorionic villi and holds the same genes as your baby. Blood taken from your placenta is therefore a good way to test for genetic diseases.

This test takes place at 11 – 13 weeks. During it, your doctor, using ultrasound, will insert a needle through your abdomen, or a catheter through your cervix, into your placenta. The results are ready in seven days, and a detailed test report takes a couple of weeks.

The results of CVS are available earlier in pregnancy than amniocentesis results. This is an advantage if the mother wishes to terminate the pregnancy due to abnormalities detected.
If you experience vaginal bleeding afterwards for more than two days tell your doctor. You should also tell your doctor if you have a fever, as it is possible you have caught an infection during the procedure.

Amniocentesis
This is a quick procedure carried out at 15 – 20 weeks, by a specialist using ultrasound to guide a long, thin needle through the abdomen into the amniotic sac. One to two tablespoons of amniotic fluid is then withdrawn. Amniotic fluid contains cells from your baby, which can be examined for information about the number and structure of your baby's chromosomes. Besides Downs Syndrome, your baby may be considered at high risk from specific disorders because of your ethnic origin or family medical history.

Many women experience cramp following amnio. Doctors often advise rest for a couple of days following this procedure, and avoiding energetic activity. If you lose a tiny amount of fluid or blood afterwards, do not be alarmed. But if you experience a large loss of fluid or blood, seek emergency medical attention.

You’ll get your results in one to two weeks, although there is a faster test called Fluorescent in Situ Hybridization (FISH). FISH results are ready in 1 – 2 days but they are not comprehensive and only test for certain common abnormalities like Down's Syndrome.

Further Amniocentesis
You may need additional amniocentesis later in pregnancy to test for infections. If you are rhesus negative, you may also need further testing for 'rhesus sensitisation', where they check your amniotic fluid for broken down red blood cells from your baby.

Foetal Blood Sampling
This takes place at 18 weeks and is like amniocentesis, except the needle is inserted into the umbilical cord. This test is sometimes used to diagnose certain infections in your baby or check if the baby has anaemia or hydrops – a condition where your baby’s body is abnormally retaining fluid.
Although this test gives you fast results (only 3 days), it has a higher risk of miscarriage than amniocentesis, and increases chance of infection and rupture of the membrane.

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