20 week ultrasound – importance of

There are three trimesters to your pregnancy – the first lasting to 12 weeks, the second to week 27, and the third running through to delivery. Your 20 week ultrasound falls almost halfway though your pregnancy.  Normally the fetus’s heart is fully formed and functioning within the first 12 weeks.

At this point your baby will be about 8 inches long and you will be feeling movements made by your baby. Watching your baby on the ultrasound screen is very emotional and it’s great if you can share it with your husband or partner and even with your other children.

Whether you want to know the sex of your baby is up to you and your partner. Your ultrasound  is mainly to find abnormalities and if your baby is in the right position it is quite likely that the sex will be revealed. You need to decide in advance whether you want to share in this information.

Almost all the hospital labs let you watch the scan as it is being performed you can watch the screen. By the way at 20 weeks twins can also be detected.

While the scan is being done your technician will often point out the different parts of your baby. When the detailed scan is being conducted that could reveal abnormalities some technicians turn the screen away. Procedure depends on the protocol of the hospital or lab.  Much of the time, if certain defects are found, further testing will be done. 

The technician will examine the baby’s internal organs. You with an untrained eye would not be able to distinguish these organs. Bones will appear white, soft tissue grey, and fluid black.

The technician will start by examining the head which should be ball shaped with a line that separates the two brain halves which have fluid around them. At the back of the head will be a dumb bell shape called the cerebellum.

The technician will also check your baby’s spine from the neck down to the shoulders and pelvis to ensure all the vertebrae are correctly aligned. The abdomen is also checked to make sure it is properly covering the organs.

Next the heart will be examined to ensure that it is properly developed, that valves are operating properly, and that the chambers are equally developed. The ultrasound has saved many lives by picking up on heart defects early so that they can be corrected.

The stomach, kidneys, and bladder will also be examined. Then the hands and feet are checked for deformities. Lastly the placenta, umbilical cord, and amniotic fluid are all checked.

Almost half of all major abnormalities can be seen on a scan by 20 weeks. However that means that half will not be seen. Here are some major abnormalities and the percentage at which they can be picked up at 20 weeks.

1. Down’s syndrome -40% – with babies with Down’s that have bowl or heart problems the scan can pick it up.
2. Anencephaly which is when the top of the head is absent – 99%
3. Exomphalos and gastroscisis which are abdominal wall defects – 90%
4. Spina bifida (open spinal cord) – 90%
5. Major limb abnormalities – 90%
6. Major kidney problems – 85%
7. Major heart problems such as defects in the chambers, valves or vessels) – 25%


8. Diaphragmatic hernia – 60%
9. Hydrocephalus which is excessive fluid within the brain – 60%.

*** Cerebral Palsy and Autism cannot be picked up with a scan.

If anything is looking abnormal you will be told and another scan will be scheduled for usually within a couple of days. If a serious problem is confirmed you will and your doctor will discuss all your options including and the risks associated with these options.

Question to ask during your 20 week ultrasound

1. Do you see 4 chambers?

2. Do you look at the arteries or outflow tracks as part of your scan?

*Note: Extremely important to focus on artery views. CHD often missed if only a standard “chamber view” is performed.

3. Are the heart and stomach in correct positions? Both organs should lay on the left side of the fetus.

4. Is the heart rate normal? Is the heart rate too slow (less than 100 beats per minute), too fast (over 200 beats per minute), or irregular? *Note: A normal heart rate range for a fetus is 120-180 beats per minute.

5. Is the heart function normal? Does the muscle work normally? Is everything hooked-up correctly?

Your 20 week ultrasound is a great way to ensure that all is progressing well with your pregnancy and to make you feel much more relaxed about your baby’s health.

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