Pregnancy Ultrasounds

There are a number of ultrasounds that may be offered to you in pregnancy. Like anything in pregnancy, you have a choice, and it is your care provider’s role to present you with the options and the evidence to facilitate you making an informed choice. While there is certainly a standard path as concerns ultrasounds in pregnancy, not everyone follows it, the choice is yours to make.

Here are the ultrasounds commonly offered:

  • Dating ultrasound:

    Typically conducted between 7 to 10 weeks of pregnancy, this can assist in determining your estimated due date. If you are confident in your dates you may choose not to do a dating scan, or you may seek to do one anyway in the hope of hearing your baby’s heartbeat.

  • First trimester ultrasound:

    Sometimes called the “12 or 13 week” scan, this is best performed between 11 and 13+6 days weeks, to identify any potential structural abnormalities. This assessment includes of baby’s nasal bone, and nuchal translucency (thin layer of fluid at the back of baby’s neck, itself a potential indicator of certain conditions). This may be combined with a blood test to form the combined screening, or alternatively you may elect to complete “non invasive prenatal screening” (“NIPS” or “NIPT”), more below.

  • Second trimester ultrasound:

    Sometimes called the “20 week” or “morphology” scan), this is the main (and for some, the only) ultrasound scan obtained during pregnancy. Completed between 18 and 22 weeks, screening of all vital organs can take place at this scan to assess for any abnormalities. The location of your placenta will also be reported.

  • Third trimester or growth scan:

    In certain circumstances a “growth scan” may be offered later in pregnancy. This should not be offered as part of standard care but may be recommended to you in certain circumstances. Like anything, you may consent or refuse it. Consider using BRAIN to make this choice.

    In some other circumstances, a third trimester ultrasound will be recommended in order to check on the location of your placenta, or to review any minor anormalities which may have been detected earlier in pregnancy (e.g. review of fetal kidneys where increased fluid identified early in pregnancy). If you are undertaking such a scan, get clear on the reason for the scan and if you have particular views about reporting on growth/size, discuss with your care provider.

Routine/regular bedside ultrasound or abdominal examination?

Some care providers (generally private obstetricians) offer a bedside ultrasound at each appointment instead of using a doppler to hear the fetal heart rate. While many parents enjoy seeing their baby on ultrasound, the Australian Pregnancy Guidelines recommend an abdominal examination and palpation, fundal height measurement (where a measuring tape is used to measure the distance between the top of your pubic bone and the top of your uterus, with each cm roughly equating to a week of pregnancy +/- 2cm, ie 37 weeks 37cm), and auscultation by doppler (listening to your baby’s heart rate using a portable device) from 24 weeks of pregnancy (although some care providers will offer it earlier).

The use of abdominal palpation promotes antenatal maternal-fetal bonding and attachment by assisting you to visualise and connect with your baby and build confidence in understanding their positioning in your body. While many parents enjoy visualising their baby on routine bedside ultrasound, some women describe this experience as feeling disconnected from their own body, in contrast to the more “embodied experience” of abdominal palpation (Bonnen et al., 2023).

Much like the evidence on the reliability of ultrasound to predict big babies (which allows for a range of error of up to 10% to be considered “accurate” — something which is significant when considering the size of babies), the evidence on the reliability of fundal height measurements is mixed. What is clear is that accuracy increases when the same care provider (another shout out to continuity of care) completes the measurement at each appointment.

Reliable or unreliable — the questions raised by growth scans are: What will I do with the information? Will it change my approach to birth? Questions that also turn on the evidence surrounding little and big babies. More on this later, but here are some resources for you in the meantime.

Resources: