What scans can you expect in your first trimester?

A lot happens in the first trimester of pregnancy for both you and your baby. We give you a heads up for this exciting stage.

Obstetric ultrasounds or ‘scans’ as they are commonly known, are highly anticipated events during a pregnancy where parents-to-be are able to gain a unique view of their developing baby while it’s still tucked away in the womb. During the first half of the pregnancy, up until 20 weeks gestation, a woman is generally unable to feel her baby moving. So, these precious moments when you are having a scan, albeit being very surreal, can be enough to reassure you that your baby is safe and well, and growing and thriving within you.
Prospective parents often go to scans with their own expectations, and in the excitement, forget the medical purpose. While most scans unfold perfectly, they can also involve moments of uncertainty and disappointment, so it’s good to be prepared. For this reason, expectant mums often take their partner or a support person along to each appointment. Thanks to technological advances, sonographers can often offer you 2D or sometimes even 3D images of your baby, as well as allowing you to record a video of the scan while being performed that you can show and send to those loved ones who can’t be with you.

To help you prepare for these appointments, here’s a guide of what to expect at each ultrasound.

WHAT IS ULTRASOUND?

Ultrasound is a non-invasive diagnostic imaging procedure that produces pictures of the inside of the body using high frequency sound waves. The sound waves travel from a small probe called a transducer, through the skin and into the body. The sound waves bounce off different tissues within the body in a different way, depending on the tissue, and the sound waves that return back to the transducer are converted into electricity. The transducer sends the electrical signals to a computer which converts them into an image. These images are captured in real time and can show the structure and movement of the body’s internal organs. They can also show blood flowing through blood vessels – this is known as a Doppler ultrasound.

ULTRASOUND IN PREGNANCY

During pregnancy, ultrasounds are performed to evaluate a baby’s development. The sonographer will put a clear odourless gel on your skin which is needed to allow the sound waves to be sent and received by the transducer. The sonographer passes the transducer over your skin overlying your uterus and baby. The transducer sends out ultrasound waves and picks them up again when they bounce back. The transducer converts the sound waves to electrical signals which are sent to the computer to create an image of your baby which is displayed on the screen. Most women will have a 12 week scan, a 20 week scan and one or more growth scans during their uncomplicated ‘singleton’ pregnancy. However, mothers carrying twins or triplets should be prepared to have more scans.

EARLY PREGNANCY ‘DATING’ SCAN (6-7 WEEKS)

Also known as the ‘dating scan’, this is the best timing to assess the viability of your embryo, your gestational age and due date. All embryos are the same size at this stage, your embryo is called a ‘fetal pole’ as it literally appears as a little line, and the measurement from the top to the bottom of the fetal pole, or crown-rump-length (CRL) is the best estimate of how many weeks pregnant you are, with an error of +/- 5 days. If this agrees with your dates by your last menstrual period (LMP) within this 5-day error margin, then your due date is derived from your LMP. If it doesn't agree, the scan is deemed a more reliable predictor of your due dates. Later in your pregnancy, baby’s growth diverges according to their varying genetic potentials and environmental exposures, so later in pregnancy, your baby’s measurements on scan are less reliable at estimating how pregnant you are.

Your embryo is usually 0.5 to 1 cm in length at this stage. The most obvious structure seen and the highlight of this scan, is seeing your baby’s heartbeat for the first time. The yolk sac should also be seen, a circular ring-like structure adjacent to the fetal pole, which confirms an intra-uterine pregnancy and contains nutrients which will help to maintain your pregnancy until the placenta takes over.

THE 12 WEEK SCAN

Since the dating scan, your little embryo has developed exponentially and is now a fully formed foetus with all of its major organs developed. Your foetus is now around 5 cm in length (by CRL) and your 12 week scan is used to confirm your due dates.

The 12 week scan is also an early structural scan of your baby, looking for some problems that can be seen this early such as spina bifida. However, a more detailed structural scan of your baby’s anatomy is performed at 20 weeks. The scan also measures the nuchal translucency, the skin thickness at the back of baby’s neck. This can be used if you opt to have the combined nuchal translucency and serum screening test which can detect some babies with Down syndrome, but it is not very accurate and can also be normal in some babies with Downs syndrome. Non-invasive prenatal testing or NIPT is a more accurate test for Downs syndrome and other chromosomal abnormalities. NIPT involves a blood test of 10 ml of your blood, is performed earlier when you are at least 10+1 weeks pregnant and detects >99% babies with Downs syndrome but also checks all your babies chromosomes including baby’s sex chromosomes and is the earliest test you can do to tell you the sex of your baby if you want to know this. Your Lead Maternity Carer (LMC) can organise this for you.