WHAT ARE CHROMOSOMAL ABNORMALITIES? SOME OF THE ULTRASOUND IMAGES USED IN THIS BROCHURE ARE COURTESY OF GE HEALTHCARE These are abnormalities that occur in a person’s genetic make-up. Further information on obstetric ultrasound, We have over 30,000 genes that are stored on 23 including fetal anatomy and 4D scanning, pairs of chromosomes. These are like strands in can also be found on our website: the centre, or nucleus, of each cell in the body. The www.ascotrad.co.nz/Our-Services/Ultrasound most common chromosomal abnormality is Down Syndrome (Trisomy 21) where there are three copies of the 21st chromosome instead of the usual two. There are other more severe chromosomal abnormalities, some of which are incompatible with life. These differ from structural abnormalities such as club feet or spina bifida. + The results so far + First trimester screening with ultrasound is 1/2 currently offered throughout the developed world THE 12 - 13 WEEK and millions of women have been examined. Eighty NUCHAL SCANS, and all other obstetric ultrasound CHROMOSOMAL ASSESSMENT SCAN percent of fetuses with chromosomal abnormalities scans, are available at these Ascot Radiology branches: have been identified accepting a 5% false positive Ascot Hospital: 90 Green Lane East, Remuera rate. This compares favourably to the detection rates TEL: (09) 520 9550 or 0800 ULTRASOUND (0800 858 727) achieved with screening based on maternal age alone EMAIL: [email protected] (a 30% detection rate) and maternal age plus serum biochemistry (a 60% detection rate). The addition of AUT Millennium: 17 Antares Place, Mairangi Bay nasal bone screening has increased the detection TEL: (09) 478 6640 EMAIL: [email protected] rate to 90%. Birthcare, Parnell: 20 Titoki Street, Parnell at ascot radiology all our sonographers and TEL: (09) 373 5988 EMAIL: [email protected] reporting radiologists have undergone extensive training in all aspects of nuchal scanning. We have ST HELIERS (From 1st June 2017): been carrying out these examinations since we first First Floor, 8-10 Turua Street, St Heliers TEL: (09) 555 9558 opened in April 1999. We are one of the few private radiology practices in To make an appointment: New Zealand to be accredited in nuchal scanning and Please call us during office hours, have all the most up to date fetal medicine software 8.30 – 5pm Monday to Friday, to allow analysis. or go to our website: www.ascotrad.co.nz/Book-A-Scan In addition, we have been further accredited to include the fetal nasal bone as part of the scan. If the nasal bone is identified during the scan, the risk of fetal chromosomal abnormality decreases quite significantly. ASCOT HOSPITAL • AUT MILLENNIUM BIRTHCARE, PARNELL • ST HELIERS About nuchal scanning For instance, if your risk after the nuchal scan and blood abnormal babies are identified as normal (false - Every woman has a risk of having a baby with Down test was very low, you may decide against having an negatives). 1.4% of normal babies will have an absent Syndrome. As you get older, the risk is increased. amniocentesis or CVS. However, if your risk was high nasal bone but 67% of babies with Down Syndrome - Your background risk is the same as anyone else of the (1 in 300 or greater) you may wish to carry on with will have an absent nasal bone. same age. (See chart below). further testing. If you have any questions during the scan, please feel free to ask the sonographer or radiologist. - The nuchal scan is a screening test for Down Please note that most amniocentesis and CVS results Syndrome and other chromosomal abnormalities. are normal. NON INVASIVE PRENATAL TESTING (NIPT) You will not get an absolute answer about your baby’s How does nuchal scanning work? There is a new screening option for Down Syndrome chromosomes from this scan. - The best time to come for a nuchal scan is from 12 called NIPT. This provides a higher level of accuracy when compared to nuchal scanning and MSS1 (the - Our measurements are combined with results from weeks until 13 ½ weeks as this increases the accuracy routine blood test). It is a user pays option and at your blood test to give you an ‘adjusted risk factor’. and chance of seeing the nasal bone. Ascot Radiology we offer this in conjunction with This takes into account your age, your blood test - The sonographer will take measurements during the counselling, as recommended by the New Zealand results, and the nuchal fold measurement. The nuchal scan to ensure the baby is growing appropriately for Maternal Fetal Medicine Network (NZMFMN). For fold a measurement of the skin thickness behind the dates. more information on NIPT, please go to our website: baby’s neck. - A few measurements of the nuchal fold will be made www.ascotrad.co.nz/Our-Services - If nasal bone assessment has been possible, this to get as accurate measurement as possible. We are information will also be used in the calculation for measuring a very small structure (usually less than 3mm) Amniocentesis & Chorionic Villus Sampling chromosomal abnormality. so the baby has to be in an optimum position. Often you To get an absolute answer with regard to your baby’s chromosomes, you will need to have another test – This adjusted risk factor often helps couples will be asked to roll, cough or sit up to help the baby either a CVS or an amniocentesis. These tests carry a decide about proceeding with further tests such as an move into a better position. Occasionally you may have small risk (1 in 500 to 1 in 1000) of causing miscarriage amniocentesis or Chorionic Villus Sampling (CVS). to fill your bladder to help us visualize the baby. and are not usually recommended unless you have a These are both more invasive tests but they do give We will make every attempt to detect the presence or - high risk from a screening test (1 to 300 or greater in absolute answers. absence of a nasal bone. a nuchal scan). Your LMC can discuss these tests with - A brief scan of the baby’s anatomy will also be carried you and help you reach your decision. out. A more comprehensive scan will be done at 18-20 AGE (YEARS) RISK FOR TRISOMY 21 CVS: This is done from 11½ weeks up to 14 weeks weeks gestation. gestation. The skin is numbed with local anaesthetic AT BIRTH AT 12 WEEKS - The measurements will be forwarded to the lab to be and a very fine needle is passed into the uterus through 20 1 in 1526 1 in 1018 combined with the results of your blood test. A copy the mother’s abdomen using ultrasound as a guide. will also be sent to your lead maternity carer (LMC). 25 1 in 1351 1 in 901 A sample of the chorionic villi is taken from the You will get your overall results at your next placenta. 30 1 in 894 1 in 596 appointment with your LMC. Amniocentesis: This is done at 15 to 17 weeks. 32 1 in 658 1 in 439 - However, if your risk is high, or if we are concerned The skin is numbed with local anaesthetic and a 34 1 in 445 1 in 297 about your scan, we will make you aware of this very fine needle is passed into the uterus through 36 1 in 280 1 in 187 before your leave the department so you can obtain the mother’s abdomen using ultrasound as a guide. 38 1 in 167 1 in 112 your results from the lab more promptly. A sample of the amniotic fluid is taken from around 40 1 in 96 1 in 64 Only about 80% of chromosomally abnormal babies the baby. 42 1 in 55 1 in 36 have thickened nuchal folds. Some look normal which Both tests obtain cells that are then grown to check 44 1 in 96 1 in 20 is why, as with all screening tests, some normal babies for any abnormality. The results can be expected in are identified as abnormal (false positives) and some approximately 2 weeks.