A guide to Antenatal Screening
The first test of any pregnancy is one that confirms the woman is pregnant. Once you know you are pregnant your first port of call Is your GP to discuss antenatal care and tests.
Antenatal screening is a way of assessing whether your unborn baby (foetus) could develop or has developed an abnormality or other condition during pregnancy. Screening is not the same as a diagnosis, it give health professionals an idea as to whether a foetus will develop certain conditions. Around 700,000 women get pregnant in the UK each year 95% of those pregnancies result in healthy babies born . In few cases there are problems with the foetus’ development. This could be serious metal or physical abnormalities. However, if there are any problems, knowing about them in advance can help parents and doctors plan for the baby's future and assess any special requirements for the birth and aftercare. For some conditions that cause physical and mental problems there is no cure, and if the baby is affected some women may wish to have a termination of their pregnancy. Women will be supported by their health carers, whatever they decide.
Mothers do not have to have screening tests and they do not provide a definite yes or no answer. It is important to both parents to carefully consider any implications of the results of a test It simply helps to establish which mothers and their babies may be more at risk of complications and offers the chance for further diagnostic tests.
The screenings can detect a range of genetic and chromosomal conditions in pregnancy, these include spina bifida, downs syndrome, sickle cell anaemia thalassaemia, HIV, hepatitis B, syphilis, and rubella. All antenatal clinics in England offer screening for these conditions.
If the tests show a high enough risk of babies developing a condition and the mothers age and medical history also increase the risk then a diagnostic test is usually offered. This is called prenatal diagnosis. Mothers are carefully selected before being offered a prenatal diagnosis as the tests are quite invasive and carry a small risk of miscarriage. Diagnostic tests that are usually offered include amniocentesis, chronic villus sampling (CVS), or ultrasound scanning Most screenings are carried out in early pregnancy, some look for problems with the mother and some look for any abnormalities with the foetus.
Blood Test
Blood tests are offered from 11-20 weeks. The levels of a number of chemicals can be measured in the mother's blood to help estimate the risk of the baby suffering from certain conditions, such as spina bifida or Down's syndrome. Different tests measure different hormones or proteins, or combinations of these, including alpha-fetoprotein (AFP), human chronic gonadotrophin (hCG), oestriol and inhibin A. If hCG and AFP are used as a screening test, this is often called the "double test". If oestriol is added to the double test, this is known as the "triple test".
Ultrasound scanning
As well as checking the size of the foetus and if there are more than one, ultrasound scans also diagnose early complications such as miscarriage. At 18-20 weeks of pregnancy, most women have a more detailed ultrasound scan. The ultrasonographer makes sure the right amount of fluid surrounds the baby, examines the baby's head, heart, spine, limbs and internal organs in detail and checks the position of the placenta (which joins the mother and foetus and allows exchange of nutrients and waste products between them). This scan can identify some physical abnormalities, such as cleft lip or skeletal abnormalities, and can confirm spina bifida if blood tests have shown the baby is at high risk. It cannot diagnose Down's syndrome
Nuchal Translucency scan
This is a screening test specifically looking for downs syndrome. It is usually done between 11-14 weeks by ultrasound scan. It measures the thickness of the layers of fluid at the back of the babies neck. Babies with downs syndrome have a thicker layer. If the layer of fluid is thicker than average then women are usually offered an amniocentesis test.
Amniocentesis test
Amniocentesis is a test women choose to have usually between 15-19 weeks of pregnancy. A fine needle is inserted into the amniotic fluid surrounding the baby. An ultrasound is used to help guide the position of the needle. This is an accurate way of finding out whether the baby has a number of genetic or inherited disorders, such as Down's syndrome or cystic fibrosis. Amniocentesis carries a 0.5 -1% risk of harming the baby or causing a miscarriage. It is usually only offered to women when screening tests show they may be at a higher risk of having a baby with a genetic disorder, or to women over 35 years old. Full results of an Amniocentesis test can take up to 4 weeks.
Chronic villus sampling (CVS)
For CVS, a fine instrument is inserted through the woman's cervix into the uterus and a sample of the chronic villi (tiny finger like projections found in the placenta) is removed. These have the same genetic material as the baby.
This test looks for similar problems as amniocentesis, although it does not test for neural tube defects. CVS is performed earlier - usually between 10 and 12 weeks of pregnancy, and the results are usually available within a few days. The results of a CVS are not as accurate as an Amniocentesis result and are technically more difficult to perform and not always fully successful. It also carries a higher risk of miscarriage about 1-2%
All mothers-to-be, have regular check ups throughout pregnancy to help diagnose any hidden health problems they may have. A few of the maternal dieses the health professionals look for is high blood pressure, urinary tract infections anaemia and diabetes. These conditions can be harmful to baby if not treated.
It is important to remember that a screening test is not a diagnostic. The results of a screening are either a screen negative or a screen positive. A screen positive result means the baby developing an abnormality is high enough to consider having a prenatal test. It does not mean that the baby is defiantly affected. Most women who have a screen positive can go on to have healthy babies. A screen negative result means that there is not a high risk of abnormality but does not mean all possible problems can be ruled out.
You do not have to have to have prenatal diagnosis if you don’t want to. For many parents-to-be it is a very difficult decision, and it is important to think about what the results would mean if they were positive.
This is a members article written by RIN1983
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