Ultrasound scans are used during pregnancy to check your baby's general wellbeing and position, or guide doctors when they're carrying out any special tests and operations.
In the UK, you'll be given two scans - the first at around ten to 13 weeks, to confirm dates and check whether you're expecting more than one baby. Between 18 and 22 weeks you'll have another scan to check that your baby is growing well and there are no abnormalities.
How an ultrasound scan works?
The process is based on a sonar device that reveals objects in fluid, which was first used by the US Navy to detect submarines during World War II. A crystal, inside a device called a transducer, converts an electrical current into high-frequency soundwaves that the human ear can't detect. The soundwaves form a beam that penetrates the abdomen as the transducer is moved back and forth. The beam reflects off material in its path, and the transducer records these “echoes”. The echoes are converted into electrical signals, which produce an image that can be displayed on a screen. The beam can only penetrate fluids and soft tissue such as the amniotic sac, kidneys, and liver. It cannot pass through bone, or register gas. An ultrasound scan is increasingly used to assess threatened miscarriage, check you're not having an ectopic pregnancy, and in infertility treatments, such as IVF, and for fetal surgery.
Your first scan
The first ultrasound scan can be a thrilling moment for you and your partner - a chance to see your baby for the very first time. Scanning equipment has been improved and refined over the years, and the technique is not intrusive. Having an ultrasound scan usually takes about 15 minutes and doesn't hurt. You'll probably be asked to drink about 600ml (20floz) of water, and not empty your bladder before arriving at the clinic. This may be a little uncomfortable, but it's worth it - a full bladder provides a clearer picture of your baby on the screen.
You should be able to hear your baby's heartbeat, and to see the gentle movement of her hands and feet, waving and kicking, as she floats in the amniotic fluid. Ask the ultrasound operator to explain the image on the screen to you as some details may be difficult to make out. Some clinics will offer you a print of the image of your baby as a memento to cherish, although they may charge you for this.
Is ultrasound scan safe?
There are no known risks to your baby from ultrasound scans. There have been some worries about long-term effects, such as hearing impairment caused by the impact of soundwaves, but recent research suggests that ultrasound is not harmful to mother or baby. The waves are of a very low intensity, and so it's safe for the scan to be performed repeatedly.
20-week ultrasound scan
A scan of your baby will show that she's healthy, how she's lying - and whether you are expecting more than one. This scan shows a baby in her mother's uterus. The baby is floating in the amniotic sac, moving around all the time. At the scan you may be able to see your baby doing things such as sucking her thumb, yawning, blinking, and urinating.
Why you have scans?
- to identify abdominal problems such as an ectopic pregnancy
- if your doctor suspects an imminent miscarriage
- to check for a multiple pregnancy
- to check the position of the placenta
- to check the growth of your baby and the amount of fluid around her.
Why your baby needs scans
- to check on her growth rate, particularly if you're not sure about the date of conception
- to check how she's lying and the development of the placenta
- to find out whether she's ready to be born if she's overdue
- to confirm that she is in the usual head down position, and not bottom down, after week 38
- to detect certain fetal abnormalities, such as spina bifida
- to monitor her during tests such as amniocentesis or fetoscopy
- to assist in operations performed on her in the uterus.
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