6 Week Ultrasound
Perhaps you’ve just found out you’re pregnant and are going to have (or have had) an ultrasound. You probably have lots of questions about early pregnancy scans. A 6 week ultrasound isn’t medically necessary; ultimately it’s your choice to have one or not.
An early ultrasound can be helpful if you’re not sure of the first day of your last period (which is used to calculate your estimated due date).
If you have irregular periods, history of miscarriages or pregnancy complications, your health care provider will likely want you to have an early scan, just to be sure everything is well.
Facts about the 6 week ultrasound
So you can quickly access what you want to read the most, here’s a list of what you need to know about your first ultrasound:
- What to expect at the ultrasound
- 6 week transvaginal ultrasound
- 6 week ultrasound and twins
- Ultrasound pictures
- Heartbeat at the ultrasound
- Your baby at 6 weeks
- Miscarriage and the 6 week scan
- Seeing no baby on ultrasound
- Are early ultrasounds necessary?
6 week ultrasound what to expect
If this is your first ultrasound examination, you might be unsure what to expect.
An ultrasound this early is usually an internal vaginal ultrasound. You’ll lie back on the ultrasound table and probably have a view of the ultrasound screen, so you can see what the technician can see.
During your ultrasound, the technician will check to see if the embryo has implanted in the uterus (and not the fallopian tubes, which is called an ectopic pregnancy), if you have twins or more babies, and if a yolk sac is present.
You might be able to see the fetal pole and even a heartbeat! But if you can only see the empty yolk sac, don’t panic! It’s very normal at this early stage.
6 week transvaginal ultrasound
If you need an ultrasound during early pregnancy, it’s likely you’ll have a transvaginal ultrasound. A specially designed ultrasound wand is inserted into the vagina, to give a clearer and more detailed view the uterus, which hasn’t grown out of the pelvis this early.
The wand will not be painful, although you will feel some pressure and maybe some mild discomfort.
An internal ultrasound allows ultrasound waves (which heats tissue) to get very close to your developing baby, particularly its brain. For this reason, some people choose to avoid unnecessary first trimester scans.
Ultrasounds from around 8 weeks pregnant are usually done externally on your abdomen.
6 week ultrasound twins
Many parents are curious to know if they’re having twins! Seeing twins at the 6 week scan is definitely possible. The exact time twins can be detected depends on the type of twins, for example, if they’re identical (from one egg) or not.
At this stage, the presence of two yolk sacs can be seen, and separate heartbeats distinguished. An ultrasound with twins will show the babies as two dark spots in the uterus.
6 week ultrasound pictures
An ultrasound this early will not show much of your baby. At this gestation, what the ultrasound technician is looking for is the size of a sweet pea.
Normally during a pregnancy ultrasound, a baby is measured by CRL (crown rump length). This means the length from the top of your baby’s head to his or her bottom – limb measurements are not included.
But because it’s so early, the diameter of the sac is what will be measured. At 6 weeks pregnant, the diameter of the gestational sac is normally around 10 millimeters, compared to 2-3 milimeters at 5 weeks of pregnancy.
Don’t be worried if you can only see a small dark circle that looks empty, as it’s very common for only the yolk sac to be visible at this early stage.
But the size and presence of the yolk sac will indicate how your baby is growing, and if everything looks normal.
Your baby’s heartbeat on ultrasound
When you’re 6 weeks pregnant, it’s the earliest possible time you might see your baby’s heartbeat. But it’s not always guaranteed to be detected this early. Especially if you conceived a little later than you expected, your baby’s gestational age might be a little less than you think.
Rest assured, if the technician notices anything concerning about your ultrasound, a follow up ultrasound will be booked in the near future to provide more information.
If detected, your baby’s heartbeat would normally be between 90 to 110 beats per minute.
Your baby at 6 weeks
Right now, your baby will be around the size of a pea – between 5 and 9mm long. Your baby looks a bit like a tadpole but is developing at a rapid pace. The vertebrae is forming as are the internal organs.
So it might not look like a lot is happening from the outside but this development takes a lot of your body’s energy right now.
Find out more in our pregnancy week by week article, 6 weeks pregnant.
Miscarriage and the 6 week scan
Pregnancy loss may be on your mind.
Most miscarriages occur in the first 6 weeks of pregnancy. Quite often, a woman may not know she’s pregnant, and has a miscarriage at the time of her expected period.
Often, women want to know if their pregnancy is viable when having an ultrasound at 6 weeks pregnant.
Once a fetal heartbeat is detected, the risk of miscarriage lowers. There are also certain factors which can increase the chance of being misdiagnosed, such as inaccurate dates for your last menstrual period, or a vanishing twin, when one twin miscarries while the other remains.
In almost all cases, miscarriage diagnosis at 6 weeks is hard to make and you will likely be asked to have another scan in a weeks’ time.
Missed miscarriages occur when the embryo didn’t form or stopped developing at some stage but there have been no signs of miscarriage such as bleeding or cramping. To prevent misdiagnosing miscarriage, health care providers will rely on certain guidelines to help decide if a miscarriage is likely at an ultrasound.
These guidelines vary depending on the area you live in but often they rely on heartbeat being detected after a certain gestation, or size of the gestational sac with embryo or yolk sac present.
Seeing no baby on the ultrasound
Seeing no baby (just a sac at this stage) could simply indicate the pregnancy isn’t as advanced as first thought. The gestational sac forms as soon as the egg is fertilised, and is the first structure to be seen on ultrasound. It can be seen via transvaginal ultrasound between 3-5 weeks pregnant.
The next positive sign of pregnancy is seeing the yolk sac. This develops within the gestational sac and provides nutrition to the developing embryo. This can be seen on ultrasound by 5 and 1/2 to 6 weeks gestation.
If there’s no gestational or yolk sac at the 6 week scan, it doesn’t necessarily mean no baby. It can mean your dates have been miscalculated. This can happen if you’re not sure of the date of your last menstrual period or have irregular cycles. Usually you will have another scan in 1-2 weeks.
If the gestational sac is empty, with no yolk sac or developing embryo by the time it should be, then it’s what is known as an ‘anembryonic’ pregnancy or a blighted ovum. This is when a fertilised egg implants in the uterus but then doesn’t develop into an embryo. It’s a very common cause of early miscarriage.
Are early ultrasounds necessary?
If it’s important to know when your baby will be due, then the earlier a dating scan is done in the first trimester, the more accurate it will be. Remember, the date doesn’t predict the exact day your baby will be born – It’s an estimate only.
Some experts, medical professionals and organisations advise against early ultrasound unless there’s a medical concern. The United Kingdom’s College of Obstetricians and Gynaecologists released a paper advising all early scans before 10 weeks of pregnancy should only be done out of medical necessity.
Find out more in our article, early ultrasounds – are they necessary?