13/01/2014 15:38 GMT | Updated 22/05/2015 10:12 BST

Antenatal Tests

What's does antenatal testing really mean and what's available to you?

First of all, be reassured that you don't have to agree to undergo any tests at all in pregnancy if you'd prefer not to. Some couples see them as (hopefully) reassuring, while others feel that they throw up dilemmas that could otherwise be avoided.

Blood tests
If you are open to the idea of some tests, however, the first you'll be offered will be at your booking-in appointment at 8-12 weeks of pregnancy. At this visit, you'll be offered a simple blood test. The sample will provide a full blood count as well as confirming your blood group and rhesus factor and screening for sickle cell disease. It will also be used to check:
* for hepatitis
* for syphilis
* for HIV
* for thalassaemia
* your rubella status.The next blood test on offer is a serum screen at around 16 weeks to check for spina bifida, anencephaly and other neural tube defects as well as Down's Syndrome.

Diagnostic tests: how to decide
After the serum screen, diagnostic tests are available which can tell you for definite whether or not your baby has certain abnormalities, but you need to consider the implications before you give your consent. Say, for instance, the serum screen gives you a higher-than-average chance of having a baby with Down's syndrome, and you are offered a diagnostic test (chorionic villus sampling or amniocentesis) to confirm this. The first consideration is that diagnostic tests carry a risk of miscarriage, so you do run the small risk of losing a healthy baby if you agree to them. If all goes well but you get a positive result, what will you do next?

Some parents would rather know in advance about any abnormality so that they can be prepared; others will come to the decision to terminate; but if you know that wouldn't consider termination under any circumstances, is it worth taking the risk of miscarrying in order to know for sure? You can get help and advice around these dilemmas from the charity ARC (Antenatal Results and Choices).

Chorionic villus sampling (CVS)
If there's a history in either of your families of inherited disorders, if you're over 35 or if a screening blood test has shown a higher-than-average risk of your baby having a disorder you may be offered CVS. The test involves passing a needle through your abdomen to take a sample of placental tissue for analysis.
CVS can detect:
● Down's syndrome
● Spina bifida
● Anencephaly
● Cystic fibrosis
● Some types of haemophilia
● Duchenne Muscular Dystrophy (DMD)
● Sickle-cell anaemia
● Turner syndrome.
There is around a 2 chance of miscarriage resulting from the test. It takes 10-30 minutes to perform and the results can take up to three weeks to come through. You may be offered amnio if:
● you're over 35.
● there's a family history of birth disorders or defects.
● you've had an abnormal serum screening blood test result.
● you want to find out your baby's sex for legitimate medical reasons.
● your rhesus status needs to be confirmed.
There are some alternatives to amnio for detecting Down's syndrome. Ask your medical team for details.

Some women are offered an early scan from around 6 weeks of pregnancy, but this is usually only if they've had fertility treatment or a history of problems in pregnancy. All women should be offered dating and nuchal translucency scans between weeks 8 and 14 – but again, you don't have to have any if you'd prefer no to. The nuchal scan measures the amount of fluid in the back of your baby's neck, which indicates the risk of Down's syndrome. The dating and nuchal tests may be combined, and some health authorities offer a blood test at the same time as an extra risk assessment tool.

You'll definitely be offered an 'anomaly' scan at around 18-22 weeks of pregnancy to look at all your baby's organs and check for normal development. Most parents go into this scan looking forward to seeing their babies for the first time, and probably taking photos away with them.

It's important to bear in mind that abnormalities may be detected, and to try to prepare for this eventuality, although the majority of babies are healthy. This is usually the last scan offered unless there's a medical problem with mum or baby, or if there are concerns about your baby's growth.