• Gillian Sims

So You Want To See Your Baby On A Screen...

First, let me be clear: In a nation of escalating obesity, increasing IVF rates, unprecedented diabetes and of more older women starting families, I am grateful for ultrasound scans (trust me) but let’s get a couple of things straight:


Because this isn’t the movies. Kiwi women are routinely offered a twelve week scan to help estimate their risk of chromosomal abnormality, and a twenty week scan to review baby’s physiological development. Outside of that, additional scans are offered for abnormalities, such as, your baby could be in a breech position (upside down) or is measuring much smaller than their gestation. Fewer scans indicate fewer clinical concerns...best to roll with it and not look for problems that are not there.


Scans performed prior to twelve weeks are not routine and offer no benefit to the care of a low risk, healthy woman. With the exception of women with symptoms like bleeding, or a history of miscarriage, so called ‘8 week scans’ serve mostly to reassure uncertain women who are still learning to trust their bodies. And uncertain GPs.

But what if I’m having twins?!

Well here’s the thing, you probably aren’t. But if you are you will still have a chance to find out early on at your twelve week NT scan, and an eight week scan will not have changed the management of your pregnancy at all. So, time to be patient! You will need the practice if you’re going to be a mama! Yes, not knowing what is going on inside your own body is hard but as midwife, the best advice that I can offer you is this:

Uncertainty is an inevitable part of parenting that does not go away;

the sooner you can make friends with it the better.

I could write a whole other blog post about this, but for now let me just say that the nature of pregnancy is both highly individualised and unpredictable therefore, raising a baby is often a crash course in learning to trust your own instincts, and scans are just not a reliable alternative. Sorry.


And no, not because we are hippies who prefer burning moxibustion sticks to ultrasound technology, but largely because - unlike other health professionals who are trained to treat illness - midwives trust women’s bodies. Because pregnancy is not an illness. Despite the best efforts of modern society, due dates remain a variable estimate to which the baby is oblivious (they're actually a due month. 97% of Kiwi babies are not born on their due date). So, regardless of when your baby was conceived, their birth will be anywhere within a four-to-five week time frame. What we have known as midwives since, well...forever, is that a woman who is sure of her last period date has a much smaller margin of error around this estimate than a woman who has been offered multiple due dates based on multiple scans. Part of the reason for this is that pregnancy scans are based on the huge assumption that every woman has a 28 day cycle, which every woman does not. So, unless you are unfortunate enough to have wildly erratic periods, or absolutely NO idea when your last period could have been, chances are a dating scan will be of little benefit to you, and possibly a source of confusion.


Sometimes a big one. How large this margin is will vary based on things such as the experience of the technician performing the scan, the amount of abdominal fat a woman carries, or how late in her pregnancy she is. Due to variables such as these, many of the measurements observed on a scan are subjective, so three different technicians may estimate three different baby weights based on the same scan (it’s true). For women who require a growth scan towards the end of their pregnancies, it is not unusual to be offered an estimated fetal weight that is plus or minus 400-500 gms either side. That’s a weight range of up to one KILO, people! Not exactly reassuring. Let’s keep this in perspective: ultrasound scans by themselves are not a reliable basis for decision making and should be factored in as one part of the whole clinical picture.


Your twelve week nuchal translucency scan is designed to estimate your risk (not diagnose. Two very different things) of having a baby with a chromosomal abnormality (Down Syndrome being only one of three), by estimating the thickness of a small fold of skin on the back of your baby’s neck. This scan is a simple measurement and in and of itself can not reassure you of much at all, other than the fact that bubs seemed happy enough at the time of the scan. The information gathered in this scan is then sent to a national testing centre in Auckland, where it is combined with the results of a maternal blood test (because the scan on it’s own is not reliable enough) to determine how likely you are to be in the mainstream population of Kiwi mums who are unlikely to have a baby with a chromosomal abnormality, OR if you could be in a small group of women who require follow up testing. No diagnosis of anything at all. Your estimated result is only about 78% reliable, and if you choose not to get the blood test done then the twelve week scan has little clinical value other than showing you a pretty picture on a screen.


The twenty week anatomy scan is intended to be a full anatomy and physiology review of baby’s development, and most often is the scan where you can find out which gender your baby is, if they are feeling cooperative. Some of the time though, that baby is not interested in cooperating with anyone who wants to peer into their privately developing mystery world, and when this happens it is documented on your scan report as ‘poor visualisation of the (developing organ - usually the heart)” and the woman is asked to return in two weeks for a follow-up scan.

All. The. Time.

So, why twenty weeks then? For two reasons, firstly because twenty weeks is considered by radiologists to be 'the sweet spot' between the baby's soft tissue organs being developed enough to visualise on screen, and the technical ability to see bone structures. The later it is in the pregnancy, the harder it is to see these structures because the sound waves of an ultrasound don't travel through bone. Secondly, because in the event that a baby is diagnosed with something unexpected, or a concern is raised such as the location of the placenta, twenty weeks is the time frame that offers the most opportunity for women to receive genetic counselling before deciding whether or not to continue with their pregnancy, or to arrange ongoing monitoring at key points during a high-risk pregnancy.


Ultrasound scans are helpful and as a Lead Maternity Carer I am grateful for them, but up until the 1950s, women were giving birth to babies without ever having seen anything on a screen, or knowing what sex they would be. In fact, when my grandmother was pregnant with twins in this era, she was sent from Rotorua to Auckland to have an X-Ray to confirm her GP's suspicions, so even then they were not widely used! Ultrasound scans are a tool which help us to generate a more detailed clinical picture when it comes to decision making, but ultimately they have their flaws, and they can, and are being overused. At the end of the day, scans are little more than a window in time which provide information regarding baby's wellbeing during the scan. No ultrasound scan can guarantee that any baby will be born safe and well, because EVERYTHING in pregnancy is subject to change. As unsettling as this might sound, making decisions based on limited information is very much a part of modern health care, just as it is parenting and as I've suggested, my best advice is to make friends with uncertainty, because it is not going away and yet-another-scan is probably not the solution you are looking for.