Obstetric nuchal dating scan
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A balance must always be maintained between diagnostic benefit and risk to the patient. A trained counsellor in the area of diagnosis and screening should be available, as should a quiet room for breaking bad news about the baby. Tissue social will be tucked into your clothing, to protect it from the ultrasound gel which will then be put on your tummy. References Kagan KO, Wright D, Valencia C, et al. NUCHAL TRANSLUCENCY SCANS 12 TO 13 WEEKS There are two functions to the Nuchal Translucency scan. The first is a sin test for Down's Syndrome, Trisomy 13 and Trisomy 18, and the second is to establish who has a high risk pregnancy with regards to Down's Syndrome, Trisomy 13 and Trisomy 18. Down syndrome is one of the most common chromosome abnormalities, affecting 1 in 600 live births. This allows for best assessment of the baby. This has an accuracy of about 70% and obstetric nuchal dating scan lead to recommendations for further testing, such as an amniocentesis. You'll also be offered a more detailed between about 18 weeks and 21 weeks of pregnancy. Several randomized controlled elements have reported no association between Doppler exposure and birth weight,and perinatal mortality.
Getting a nuchal scan All pregnant women will be routinely offered the nuchal translucency scan as part of their antenatal care. The scan needs to be done between 10 weeks and 13 weeks plus six days gestation, so many hospitals will include the test as part of your. It is up to you whether you want to have it. What happens during a nuchal scan and what do they measure? During the scan, the sonographer will measure the amount of fluid at the base of your baby's neck. On the scan it looks like a black space at the top of the spine. All babies have fluid at the base of the neck, but many babies with Down's syndrome will have an increased amount of fluid. A measurement of 3mm and above indicates a higher risk of Down's syndrome. At the same time, the sonographer will check to see whether a nasal bone is visible on the scan. Studies have shown that three in four foetuses with Down's syndrome do not have a visible nasal bone at this. The foetus will be measured and the precise gestational age calculated. This information, along with the mother's age will be entered into a statistical analysis program and the odds of your baby being born with genetic abnormalities will be calculated. The scan cannot tell you conclusively whether or not your baby will have Down's syndrome — it can only estimate the level of risk. For example, if your result is one in 5,000, that means that if you had 5,000 babies, one would have Down's. If your result is one in 150 or less, it is considered high. What do the results mean? At the end of the day, any screening test is just that — a risk assessment. It's not a diagnostic tool. It is important to remember that after the nuchal scan you are given a percentage of risk, not a diagnosis. It is an indication of the likelihood of Down's syndrome and other genetic abnormalities. Before your scan, your risk will be calculated based on your age only. The majority of women will receive a reassuring test result, as the risk will be lower than the risk calculated on age alone. Further investigations will be recommended for anyone with a risk higher than 1 in 150 although some NHS trusts use 1:300 as the cut-off point. Combined screening Most hospitals offer a combined test, which includes a alongside the nuchal scan. This test will look at the levels of two hormones: pregnancy-associated plasma protein—A and free beta—hCG in the mother's blood. These levels may indicate a higher risk of chromosomal abnormalities. This information will be combined with the data from the nuchal measurements along with the general risks for the mother based on her age. Combined screening offers a slightly more informed risk percentage, although it is still not a diagnostic test and cannot be completely accurate. How accurate is the nuchal translucency test? Screening tests cannot be 100% accurate and, according to NHS Choices, the nuchal translucency scan has a false-positive rate of between 3. It has a false-negative rate of 30%, which means that 70 of every 100 cases of Down's will be detected by the test. What are your options if you have a high risk of Down's syndrome? We were given a one in three risk of Down's following the combined screening, mainly due to the blood test. As the risks were so high we got lots of info and were fast-tracked to invasive testing. There were no major chromosome abnormalities detected, but the wait was the most difficult bit. As the nuchal test and the combined screening only give an indication of risk, you will be offered a more definitive test — CVS or — to give a more accurate indication of any genetic abnormalities. CVS and amniocentesis have much lower error rates: amniocentesis has a false-positive rate of 0. These tests are invasive and carry the risk of about 1 in 100, according to the NHS so it will be up to you to decide if this further testing is right for you. The best thing you can do is try to forget about the tests until you get the results, as the discussing, backwards and forwards, and the waiting was what drove me crazy.
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