When should I have my first pregnancy scan? Well, the general guidelines suggest between 8 and 14 weeks for the first ultrasound scan. However, what appears sometimes to be overlooked is the critical measurement for Down syndrome which must be done before the foetus has reached 13 weeks 6 days or 84mm in length from the top of its head to the base of the spine.
What is an ultrasound scan?
An ultrasound picture is formed using sound waves which are passed through the uterus and reflected back as an image on a screen. The sonographer will apply a gel on your lower abdomen and he or she will move the scanner over the gel, sometimes pressing down, until the uterus (womb) and foetus can be seen. You will be advised to drink a litre of water around an hour before your scan to ensure your bladder is full, pushing your womb up which assists the sonographer to detect the foetus more easily.
What do ultrasound scans check for?
- the measurements of your baby allowing a more accurate dating of how many weeks pregnant you are and for the due date.
- to check for multiple pregnancies
- to check for abnormalities, particularly in the baby’s head, abdomen, limbs or spine.
- to show the position of your baby and the placenta. e.g. for a low placenta in late pregnancy, special care may be needed at delivery or a Caesarian section may be advised
- to check that the baby is growing and developing normally (particularly for multiple pregnancies.
- to determine the baby’s heart rate
- to identify problems of the uterus, placenta, cervix or ovaries
- to look for possible ectopic pregnancies or the chances for miscarriage
A nuchal scan helps to identify higher chances for chromosomal conditions including Down Syndrome in a foetus, particularly for older women who have high risks. High thickness measurements are also associated with congenital heart defects. The scan is carried out between 11 – 13wks 6days pregnancy and assesses the thickness of the soft tissues of the nape of the foetus’ neck. There are two distinct measurements, the Nuchal translucency, which is measured earlier in the pregnancy at the end of the first trimester, and for which there is a lower threshold for increased diameter, and the nuchal fold, which is measured towards the end of the second trimester. Foetuses with Down Syndrome tend to have a higher amount of fluid around the neck. This scan is best combined with your first trimester blood tests for a more accurate determination of these conditions, generating more reliable results.
My Scan – Don’t Make The Same Mistake!
Well, my first scan didn’t go quite according to plan. I asked for the first available appointment, booked the blood tests for the same day to follow my scan and discovered on the day that my baby fell just outside the measurement limits for the Down Syndrome assessment. The sonographer measured 86.4mm, a mere 2.4mm over the maximum of 84mm for the software to make the assessment! I was three days over the maximum time limit too! Additionally, the blood test had to be cancelled and rescheduled for a week later to be safely within the second trimester window for a valid test! I was infact 14 weeks 3 days into my pregnancy!
This left me feeling very anxious and annoyed that I hadn’t been given the possibility to have the test within the prescribed timescale. Now the only non-invasive test I have for Down Syndrome is the second trimester blood test which is done between 15 and 20 weeks of pregnancy. It measures the blood level of four pregnancy associated substances, alpha fetoprotein, estriol, HCG and inhibin A.
So now I have to play the painful waiting game and with less certainty from the second trimester blood tests than I may have had with a Nuchal scan during the first trimester. Ladies, don’t leave it to chance, challenge the appointment timescale for that all important first scan! Sadly, I didn’t realise how critical this was.
Post by Adriana
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