Amniocentesis, triple test and quadruple test
Routine screening for genetic disorders such as Down's syndrome and blood disorders like sickle cell can only give an indication of the possible risk your baby has of having any abnormalities or birth defects.
If you're found to be at high risk, you may be offered more definitive tests, including amniocentesis, that give you a more reliable indication of the health of your baby.
Other reasons you may be offered an amniocentesis include:
- Having a previous pregnancy that was affected by a genetic disorder
- You or your partner have a family history of genetic disorders
- There have been any abnormal results from any screening tests you have had
What can amniocentesis show?
Amniocentesis cannot detect all birth defects but it can be used to test for:
• Down's syndrome • Edwards' sydrome • Patau's syndrome • Sickle cell disease • Thalassaemia • Cystic fibrosis • Muscular dystrophy • Tay-Sachs disease • Neural tube defects such as spina bifida • Rhesus disease • Infections
What happens during amniocentesis?
Amniocentesis involves taking a sample of the amniotic fluid, which is the water that surrounds your baby in your womb.
During the procedure, a needle will be pushed through your abdomen and uterus, guided by ultrasound so that it will be done away from where you baby is lying.
The amniotic fluid is then analysed because it will contain cells from your baby.
The procedure is normally done between weeks 16 and 22.
What are the risks? Is it safe?
Amniocentesis is an invasive test and so does involve risks to you and your baby. The increased risk of miscarriage is about 1:100.
There is also a risk of infection, which could be caused by the needle puncturing the bowel or from contaminants entering the woman's body from the needle. This will happen to less than 1:1,000 women.
The actual test is not painful, and there is no need for an anesthetic. If you feel unwell after the test, you feel shivery or you feel like you are having contractions, go and see a doctor for advice.
Small amounts of blood and a little cramping after the procedure are not uncommon, but it's worth taking it easy for several days after the amnio.
If you are rhesus negative, there may be a risk of sensitisation and you may need an Anti-D injection.
When will I get the results?
There are two different types of test done on the amniotic fluid tested after an amnio. A rapid test will identify Down's, Edwards' and Patau's syndrome. The results are ready in three working days and they are almost 100% accurate.
The full karotype test takes a bit longer (up to three weeks). This is very accurate, but around 1% of tests will not be conclusive.
What are your options?
Although a negative test result will not rule out all genetic disorders, it will rule out the ones that have been specifically tested for. If you get a positive test result, it can be very upsetting, because it throws your imagined future into disarray. You may need counselling to help you adjust. And Mumsnet can be tremendously helpful, because there are umpteen women who've faced similar circumstances and can offer you insights and empathy.
You may wish to end your pregnancy and the methods used to do this will vary according to the stage you are at - you will be given advice about this by your GP or midwife.
No one can make the difficult decisions for you, but the experiences and opinions of those who've had to make the decisions for themselves can help prepare you for whatever the tests and scans show up. Don't agonise alone, get support from other Mumsnetters.
Triple and quadruple tests
There are two screening tests for genetic disorders after the first trimester and they are both based on blood tests that will be taken between 15 and 20 weeks gestation. The triple test looks at these markers in the blood:
- Human chorionic gonadotrophin (hCG)
- Oestriol (uE3)
- Alpha fetoprotein (AFP)
The quadruple test includes one more marker: inhibin A.
If your baby does have Down's syndrome there will be higher levels of hCG and inhibin A in your blood and lower levels of AFP and uE3. The test can also diagnose Edwards' syndrome, neural tube defects and Patau's syndrome.
The triple and quadruple tests are not diagnostic tests. The triple test is about 70% accurate and the quadruple is slightly more sensitive and has a detection rate of 81%.
Some places will offer an integrated test, which will consider first trimester combined tests along with the triple and quadruple test. This is the most accurate non-invasive screening test for Down's at 96%.
What Mumsnetters say about amniocentesis
- The amnio itself wasn't too bad - the needle didn't hurt, and withdrawing the fluid was a weird and slightly uncomfortable pulling sensation, but to be honest the most painful thing was my partner squeezing my hand too hard. whinegums
- I've had two amnios. It's uncomfortable rather than painful, but you do worry about the risk of miscarriage. I suppose it all depends on what you would do with a result that told you your baby had a trisomy eg Down's/Edwards/Patau syndrome. Bundle
- I watched the screen while the doc was doing it and my son (I was 16 weeks pregnant) moved as far away from the needle as possible and then really curled into the foetal position. It was a bit surreal to be honest. shabster
- I wanted a diagnostic test that would tell me 'yes' or 'no'. I understood all the risks and I honestly don't know what I would have done if the results had not been normal. I did what was right for me and my husband, and you must do what is right for you. Christie
- I know a lot of people say they would not terminate a the pregnancy if they were having a baby with an abnormality so there is no point having an amnio, but it is also useful, if the baby does have an abnormality, to prepare for the birth and arrange any necessary care the baby might need immediately after birth. WestCountryLass
- You can discuss your scan results in our Antenatal tests and choices Talk forum