It's becoming increasingly uncommon for pregnant women to have their very first ultrasound at 20-week, though this used to be the first opportunity for most pregnant mums to be able to see their baby inside the uterus. It was a long wait to say the least. But now it's more common for women to be having their second ultrasound at 20 weeks gestation; the first is generally offered at around 12 weeks to screen for chromosomal abnormalities.

Another name for the 20-week ultrasound is a foetal anomaly or foetal morphology scan and it can be done anytime between 18-20 weeks of gestation. If you don't have the opportunity to have a screening ultrasound until 22 weeks of gestation, then this may be fine as well. The purpose of this scan is to assess for foetal development and growth as well as providing a means of detecting any foetal abnormalities which may relate to their structural development. In addition, their period of gestation (to see if it matches with the mother's dates), the position of the placenta and the baby's heart, lungs and organs are all checked. It is also an opportunity for parents to find out the sex (gender) of their baby. Gender prediction is fairly accurate at this stage.

A 20-week ultrasound uses the same technology as all other trans abdominal ultrasounds. Using high frequency pulses of sound waves which pass from a transducer and then bounce off the internal structures of the baby and amniotic fluid surrounding it. Remember that the 20-week ultrasound is a diagnostic and screening scan a medical procedure rather than simply a way for parents to have a peek at their little one. Of course, there are the additional benefits of getting to see your baby up close and personal, but this is an added bonus to the real reason why a foetal morphology/anomaly ultrasound is done.

Do I have to have a 20-week ultrasound?

No, you don't, even if your your maternity care provider recommends one. You still have the ultimate say in whether you consent to one or not. Some mothers prefer to wait and see what their baby looks like and want to leave nature to take its own course.

In fact, feelings can run very deep for some parents in relation to being confronted with their baby having a potential abnormality. For them, the issue of perhaps being faced with the dilemma of knowing what to do in terms of continuing with the pregnancy is enough to decline the recommendation of a screening ultrasound. Spiritual and religious beliefs also factor strongly.

Others are genuinely fearful of what the 20-week ultrasound may detect. Some are unable to face their fears and choose to avoid the experience altogether. Occasionally, in cases where there is a family history of genetic disorders, counselling may be necessary to support parents in making the right choice for them.

Some parents prefer to retain the mystique and surprise of meeting their baby for the first time when it is born. There can also be the feeling amongst some couples that in days gone by, ultrasound was not available, and the majority of pregnancies evolved into healthy, well, full term babies. Adopting this philosophy just sits well for some expectant couples.

Will the 20-week ultrasound be clear?

Yes, you'll be amazed at what detail the ultrasound will provide. Be prepared to feel very connected with your baby and perhaps overwhelmed by feelings of love. Many mothers cry when they see their baby in such a realistic way and partners can feel similar feelings as well. For partners who've not experienced pregnancy symptoms first hand, seeing their baby on an ultrasound screen can the first time they really, truly believe the baby exists. Not that this is a commonly discussed issue, but it is still a fact.

The ultrasound will pick up images of your baby's organs in a series of cross sections. This can be confusing at first, until you become used to the images and your eyes adjust. Your baby's bones will be white on the screen and the amniotic fluid will appear as black. Their tissues will be grey and have a speckled appearance.

What does a 20-week ultrasound detect?

Sonographers have a check list of what they need to look for when doing the 20-week ultrasound. They start off with the basics and work their way through a range of observations including:

• Checking how many babies are present. If this is your first scan it's important to know if you are carrying one or more babies.
• The lie or position of the baby.
• Your baby's spine and abdominal wall.
• The size, weight and general appearance of your baby.
• If the size of your baby is matching your gestational assessment.
• The position of the placenta and cord and the amount of amniotic fluid. If the placenta is assessed as lying low, a repeat ultrasound at 30 weeks gestation may be recommended.
• Your baby's brain, heart, lungs, stomach, oesophagus and trachea, kidneys and general anatomy.
• The limbs, the fingers and toes (counted) the facial appearance and lips/palate.
• Measurements of your baby's head, biparietal diameter, length and a measurement of their femur (long bone in the thigh) will also be taken. These measurements are compared with the average for babies of the same gestation.

Will my 20-week ultrasound detect all abnormalities?

No, the 20-week scan does not provide 100% detection of any or all abnormalities. Some abnormalities may not be obvious until the baby is born. Heart defects and bowel obstructions in particular may not develop under later in gestation.

What if an abnormality is detected during my 20-week ultrasound?

Depending on the imaging service you have accessed, findings from your scan may be given directly to you and a report sent to your maternity care provider. Alternately, you may be advised to speak with your maternity care provider, or an appointment may be made for you to speak with a specialist obstetrician.

The ultrasound findings will be examined and reported on by a specialist sonographer and/or radiologist. Depending on the level of concern, another ultrasound with further diagnostic testing may be ordered.

Sometimes an abnormality or soft marker is detected on ultrasound and this causes parents a lot of anxiety and stress. But in the coming weeks, as the pregnancy progresses, it's not uncommon for slight deviations from normal to resolve themselves without any specific treatment or management. Therefore, a repeat ultrasound may be recommended.

Are we having a boy or a girl?

One of the big bonuses of having a 20-week ultrasound is that it is possible at this stage of gestation to see if your baby will be a boy or a girl. But if you or your partners are keen to keep this a surprise until the baby is born, then tell the sonographer before they begin the procedure. If one of you wants to know but the other doesn't then the sonographer might offer to write the baby's gender on a piece of paper and place it in an envelope to be read later. But remember, the best the sonographer can advise is your baby is likely to be one gender or the other. No, 100% guarantees of gender are provided from an ultrasound.

Be aware though that sometimes it is very clear on the screen what sex the baby is, so any plans to keep this a secret until you meet your little one face to face cannot be realised. Alternately, your baby may be lying in a position where it is not possible to see their genitals and unless they are willing to move around a bit, their sex will remain a mystery.

It's common for expectant parents to be given a photo of their 20-week ultrasound. This can be viewed later at your own leisure and if you want to, shared with your friends and family. It has become routine for imaging centres to request parents that no photographs or videos are taken during ultrasounds and any recordings or images can only be supplied by the sonography service.

This is due, in part, to the possibility of litigation if complications arise and they've not been detected during the ultrasound. You may also be asked to sign a disclaimer/permission form before your procedure.

What do I need to do to prepare for my 20-week ultrasound?

Nothing specific. Other than make the booking and ask your partner to be there as well. Allow some time for your appointment to be late or perhaps run overtime. This way you won't be rushed and too stressed to enjoy it. Also, allow some time after the procedure for you and your partner to have a coffee or lunch to chat about the scan and how it went. The procedure normally takes around 45 minutes from start to finish. It's not every day you'll have a 20-week ultrasound and you'll want to make the most of the experience.

You won't need to have a full bladder for this ultrasound, unlike the 12-week one. But the sonographer may request you don't wee for 30 minutes or so before your procedure as some urine in your bladder will help with visualising the baby. This is because a semi full bladder will help to push your uterus up higher in the pelvis, making it easier for the sonographer to see.

Don't worry if the sonographer seems so focused on the procedure that they don't constantly talk to you. Where there are good windows of time for them to describe what they're looking at and are able to share this with you, they will.

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