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The nuchal translucency scan also called the NT scan uses ultrasound to assess your developing baby's risk of having Down syndrome DS and some other chromosomal abnormalities, as well as major congenital heart problems. The NT scan measures the clear translucent space in the tissue at the back of your baby's neck. Babies with abnormalities tend to accumulate more fluid at the back of their neck during the first trimester, causing this clear space to be larger than average. The NT scan is not invasive. The NT scan must be done when you're between 11 and 14 weeks pregnant, because this is when the base of your baby's neck is still transparent. The last day you can have it is the day you turn 13 weeks and 6 days pregnant.
Find out more about the combined screening test for Down's syndrome.
You will not be offered the combined screening test if your dating scan happens after 14 weeks. Instead, you will be offered another blood test between 14 and 20 weeks of pregnancy to screen for your chance of having a baby with Down's syndrome. This test is not quite as accurate as the combined test.
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At 8 to 14 weeks of pregnancy, you should be offered a pregnancy dating scan. It will let you know a more reliable due date and check how your baby is developing. A dating scan is an ultrasound examination which is performed in order to establish the gestational age of the pregnancy. Dating scans also reveal other important information such as: the number of fetuses and gestation sacs. the presence of a heart beat. the size of the fetus, from which the gestational age is estimated. Reliability. Early transvaginal ultrasound, the most reliable way to determine a pregnancy due date, can date a pregnancy within a few days and is more accurate than determining a due date by the date of the last menstrual period.
Bottle feeding advice Sterilising bottles Combining breast and bottle Making up infant formula Types of infant formula Infant formula: common questions. Newborn blood spot test Newborn hearing test Newborn physical examination. What you'll need for your baby Washing and bathing your baby Getting your baby to sleep Soothing a crying baby How to change a nappy Nappy rash First aid kit for babies Baby car seats and car safety. Your age is factored in because although anyone can have a baby with a chromosomal abnormality, the risk increases as you age.
For example, your likelihood of carrying a baby with Down syndrome ranges from approximately 1 in 1, at age 25 to 1 in at age Because a baby's nuchal translucency normally gets a bit thicker with each day of gestation, researchers have been able to establish how large the translucent area should be each day during the three weeks the screening can be performed.
Accuracy of ultrasound to determine date of conception
They've also calculated the statistical relationship between this measurement, the baby's age, the mother's age, and the likelihood that the baby will be born with certain abnormalities. In general, the thicker the nuchal translucency at a given gestational age, the higher the chance of a chromosomal problem. You may get the results right away, or you may have to wait up to 10 days if the doctor has to send the data to a processing center. You'll want to talk with your practitioner or a genetic counselor about how to interpret the results because unless you have a lot of experience with statistical analysis and evaluating the results of medical tests, the results can be confusing.
And even if you're a wizard with statistics, you'll need help understanding your options. You'll get your results in the form of a ratio that expresses your baby's chances of having a chromosomal defect.
For example, you may be told that your baby's chances of having Down syndrome are 1 in 30 or 1 in 4, A risk of 1 in 30 means that for every 30 women with this same result, one baby will have Down syndrome and 29 will not.
A risk of 1 in 4, means that for every 4, women with this result, one baby will have it and 3, will not.
The higher the second number, the lower the risk. You may also be told that your results are "normal" or "abnormal," depending on whether they are below or above a specified cutoff. For example, some tests use a cutoff of 1 in So a result of 1 in 4, would be considered normal because the risk that there's a problem is lower than 1 in A ratio of 1 in 30 would be considered abnormal because that risk is higher than 1 in Remember that a normal screening result screen negative isn't a guarantee that your baby has normal chromosomes, but it does suggest that a problem is unlikely.
Likewise, an abnormal screening result screen positive doesn't mean that your baby has a chromosomal problem - just that he's more likely to have one.
Most screen-positive babies turn out not to have a problem: Only about a third of babies with an increased nuchal translucency measurement turn out to have chromosomal defects. If your baby's nuchal translucency measurement is above the 99th percentile for his gestational age, he's considered to be at increased risk for major congenital heart disease as well, so you'll be given a special ultrasound called a fetal echocardiogram. If your baby has a heart defect, he'll need to be monitored with regular ultrasounds and delivered at a medical center equipped to handle this condition.
Screening tests aren't perfect. They don't detect all cases of Down syndrome, so they may identify your baby as being at low risk when she really does have Down syndrome. This is called a false negative result, and it might lead you to decide against diagnostic testing that would have revealed a problem. Conversely, screening may identify your baby as being at high risk when she is fine a false positive.
Ultrasound is an amazing tool for tracking the development of a pregnancy, and it gives doctors a lot of useful information for providing optimal prenatal care. It also, of course, gives you the first glimpse of your baby! Press shift question mark to access a list of keyboard shortcuts. Keyboard Shortcuts. Play/Pause SPACE. Increase Volume ^Author: Krissi Danielsson. Fractures occur in up to 52of child abuse cases [1, 2].In contrast to accidental fractures, most abusive fractures occur in children younger than 3 years; 80of such fractures occur in children younger than 18 months .Abusive fractures may be multiple and of different ages [4, 5], a point that can only be determined from their cbeebies-games.com fractures may also highlight Cited by: The person performing the scan is called a sonographer. You may need to have a full bladder for this scan, as this makes the ultrasound image clearer. You can ask your midwife or doctor before the scan if this is the case. The dating scan usually takes about 20 minutes. Find out more about what happens during a pregnancy ultrasound scan.
This may cause you to undergo further testing and to worry about your baby's well-being unnecessarily. The reliability of a test can be seen in its detection rate. This tells you how good the test is at identifying babies that are truly affected as being high risk.
Dating scan reliability
Specifically, it's the percentage of affected babies who show screen-positive results, out of all those being screened. The NT scan alone will detect about 70 to 80 percent of babies with Down syndrome depending on which study you look at.
Krissi Danielsson, MD is a doctor of family medicine and an advocate for those who have experienced miscarriage. Every pregnant woman wants to know her due date, and a due date that is calculated from her last menstrual period with a due date calculator often doesn't match the due date that is estimated by her first ultrasound (also known as a Author: Krissi Danielsson. Accuracy of ultrasound to determine date of conception. Resolved Question: The first scan was ONE month off the mark (least likely). ALL the remaining scans continued to be one month off the mark (least likely) This is the only situation, and it is impossible. The dating scan can include a nuchal translucency (NT) scan, which is part of the combined screening test for Down's syndrome, if you choose to have this screening. The second scan offered to all pregnant women usually takes place between 18 and 21 weeks of pregnancy. It is sometimes called the mid-pregnancy scan.
The detection rate for the NT scan plus a first-trimester blood test ranges from 79 to 90 percent. These numbers mean that if you're carrying a baby with DS, there's a 79 to 90 percent chance that the combined screening will detect the abnormality and give you what's called a screen-positive result indicating that further testing is recommended.
It also means there's a 5 to 21 percent chance that the tests will miss the DS and give you a screen-negative result.
This does not mean that a screen-positive baby has a 79 to 90 percent chance of having Down syndrome. It just means that 79 to 90 percent of babies who have DS will have screening results that are suspicious enough to recommend diagnostic testing.
And 5 to 21 percent of babies who have DS will be determined to be at normal risk - that is, the results will be misleading. These tests also have a 5 percent false-positive rate. A false-positive result is one that suggests there may be a problem when, in fact, there is no problem. So a 5 percent false-positive rate means that 5 percent of the babies with normal chromosomes who are tested will be screen positive -that is, the test will show them to have an increased risk for Down syndrome even though they're not affected.
Based on a false-positive result, the mother may go ahead with invasive diagnostic testing that she otherwise might not have. And she'll probably worry more, too, until she knows for sure that the baby is fine. With the help of your practitioner or a genetic counselor, you'll want to decide whether the results indicate a high enough risk that you want to have CVS or amniocentesis to get a definitive diagnosis.
How Is Your Baby's Due Date Determined?
In making your decision, you'll need to weigh your need to know about your baby's condition against the small chance that diagnostic testing could cause a miscarriage. Individual parents must decide for themselves what risks are acceptable. If you decide not to have diagnostic testing, you can get more information about your baby's health and development by following up with the quad screen a blood test in the second trimester as well as a detailed ultrasound at 18 to 20 weeks.
This ultrasound can detect "soft markers" of chromosome disorders, such as short limbs, a bright dot in the heart, a bright bowel, and certain problems in the kidneys. It can also look for anatomical defects, such as spina bifida. Practice bulletin Screening for fetal chromosomal abnormalities. American College of Obstetricians and Gynecologists. Borrell A, et al. First-trimester screening for trisomy 21 combining biochemistry and ultrasound at individually optimal gestational ages.
An interventional study. Prenatal Diagnosis 24 7 Muller F, et al. First-trimester screening for Down syndrome in France combining fetal nuchal translucency measurement and biochemical markers. Prenatal Diagnosis 23 10 Rozenberg P, et al. Screening for Down syndrome using first-trimester combined screening followed by second trimester ultrasound examination in an unselected population.
American Journal of Obstetrics and Gynecology 5
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