During pregnancy, ultrasounds allow your doctor to check on the growth and development of your baby. They use sound waves to create images of your baby in the womb. Ultrasounds are considered very safe for both mother and baby. In your third trimester, you typically have at least one ultrasound, but some women have more.
First Trimester Ultrasounds
In the first trimester, between weeks 6-13, most women have one ultrasound. This is called the dating ultrasound and is done to:
- Confirm the pregnancy
- Determine your due date
- Check the baby’s heartbeat
- Look for any potential problems or complications
This ultrasound is often done transvaginally in the early stages for a clearer image. As your pregnancy progresses, ultrasounds are done transabdominally with a wand moved over the belly. Some women may have additional first trimester ultrasounds if any issues are suspected, like miscarriage risk or ectopic pregnancy.
Second Trimester Ultrasounds
The second trimester spans weeks 14-27. During this time, you will likely have at least one standard ultrasound around weeks 18-22.
The main purposes of this ultrasound are to:
- Check the baby’s growth and anatomy
- Look at the placenta, amniotic fluid and umbilical cord
- See fetal movement
- Check for any birth defects
- Determine the sex of the baby (if desired)
This ultrasound provides a detailed look at the development of the baby’s brain, heart, face, hands, feet and organs. Your doctor will ensure everything is progressing as expected. Some mothers may opt for additional ultrasounds during this trimester for keepsake photos or to monitor identified issues. This is also when the fetal anatomy survey ultrasound is typically conducted.
Fetal Anatomy Survey
The fetal anatomy survey, also called the level 2 ultrasound, provides your doctor with detailed anatomical information to screen for any abnormalities or problems. This ultrasound is usually done between 18-22 weeks and thoroughly examines:
- Brain and spinal cord
- Heart chambers, vessels and valves
- Stomach, kidneys and bladder
- Bones and muscles
- Face and neck
- Umbilical cord
The ultrasound technician will take measurements and evaluate each part of the anatomy. If any potential issues are seen, additional testing may be recommended. This survey provides reassurance that fetal development is on track.
Third Trimester Ultrasounds
Now we get to the main question – how many ultrasounds do you have during the 28-40 week third trimester?
In an uncomplicated pregnancy, you will likely have at least one ultrasound during the third trimester. However, some women have additional ultrasounds during this time frame for various reasons:
- Growth monitoring ultrasounds – For women whose babies were measuring small or large at prior scans, repeat third trimester ultrasounds may be done to track growth. They check the fetus’s weight and position and the amount of amniotic fluid.
- High-risk pregnancy ultrasounds – Women with identified complications like gestational diabetes, preeclampsia or placental issues often need third trimester ultrasounds to monitor their baby’s health and development.
- Cervical length checks – Women at risk of preterm labor may have transvaginal ultrasound cervical length exams to assess the risk of early delivery.
- Biophysical profile – This nonstress test combines ultrasound with fetal heart rate monitoring to check on the baby’s wellbeing later in pregnancy.
- Repeat anatomy scan – If any potential issues were seen on the earlier anatomy ultrasound, your doctor may want to take another look later in pregnancy.
- Position check – As you near your due date, ultrasound can be used to confirm if your baby is head down in preparation for birth.
The number of third trimester ultrasounds you get depends on your individual situation. Some women have 1-2 scans, while others have them weekly or biweekly in the late stages of pregnancy. Your doctor will determine if additional ultrasounds are recommended for you based on your health, risk factors and prior ultrasound findings.
Common Third Trimester Ultrasound Checks
Here is more detail on some of the most common reasons for third trimester ultrasounds:
Fetal Growth Ultrasounds
If earlier scans revealed accelerated or restricted fetal growth, your doctor will likely want to monitor this closely in the third trimester. These growth check ultrasounds usually include:
- Estimating fetal weight based on measurements
- Looking at growth patterns compared to prior ultrasounds
- Checking the placental appearance and umbilical cord blood flow
- Measuring the amniotic fluid level
Your doctor will determine how often growth scans are needed depending on the severity of small or large measurements. It may be every 2-4 weeks or more frequently down the stretch if it could impact the delivery plan.
High-Risk Pregnancy Ultrasounds
Women with identified complications or risk factors often require extra third trimester ultrasounds. These may include conditions like:
- Gestational diabetes
- Hypertension/preeclampsia
- Placental problems
- Carrying multiples like twins
- Autoimmune disorders
- Kidney disease
- History of pregnancy loss
These extra ultrasounds allow close monitoring of the fetus for wellbeing and growth. Women with high-risk pregnancies commonly have ultrasounds every 2-4 weeks in the third trimester, or more often if the situation calls for it.
Cervical Length Assessment
Women at increased risk of preterm birth may have transvaginal ultrasound cervical length screening in the third trimester. This looks at the length and dilation of the cervix to determine the risk of early labor.
Shortening and opening of the cervix happens in preparation for childbirth. Premature changes could indicate higher risk of preterm delivery. Based on the cervical length and funneling observed, your doctor can take any needed steps to help prevent early labor.
Biophysical Profile
This nonstress test is commonly done in the last weeks of pregnancy. It combines ultrasound with electronic fetal heart rate monitoring. The biophysical profile evaluates:
- Fetal breathing motions
- Body movements
- Muscle tone
- Heart rate reactivity
- Amniotic fluid volume
Each parameter gets scored. The results provide information about the health and wellbeing of your baby as you near delivery. If concerning findings are seen, your doctor may recommend delivering sooner rather than later.
How Many Ultasounds are Too Many?
There are no hard rules for the number of ultrasounds considered safe during pregnancy. Some women have 10-15 over the course of 9 months, while others may only have the standard dating and anatomy scans. Here are a few things to keep in mind:
- Medically indicated ultrasounds based on health conditions and concerns do not have limits, as they provide important information about the wellbeing of mom and baby.
- Ultrasounds should only be done when there is a medical need for them. Extra scans just for fun should be avoided.
- Research has not conclusively identified risks from numerous ultrasounds. But until more is known, most experts say additional scans should be limited without medical reason.
- Keepsake 3D and 4D ultrasounds are not recommended for safety reasons. Standard 2D ultrasound is preferred.
- Every scan done should provide useful data to guide pregnancy care. Scans that don’t give your doctor meaningful information are hard to justify.
Discuss any ultrasound concerns you have with your prenatal provider. They can explain why they recommend particular scans for you and how often they should be done.
Preparing for Your Ultrasound
To get the clearest images during your ultrasound, there are a few things you can do to prepare:
- Drink extra water before the scan so you have a full bladder.
- Avoid emptying your bladder right before the ultrasound.
- Wear comfortable clothes that are easy to expose your belly.
- Arrive on time for your scheduled appointment.
- Relax during the test and limit movement.
- Ask when/how you will get the results.
Having a full bladder helps push your uterus up so there is less tissue for the ultrasound waves to pass through. This provides better visualization of the baby. Let your technician know if you feel any discomfort or need to empty your bladder.
Conclusion
During pregnancy, ultrasound provides important monitoring of fetal growth and development. In your third trimester, you will likely have at least one ultrasound, but may have more depending on your individual circumstances.
Women with identified complications often need growth monitoring or biophysical profile scans in the last weeks before delivery. Your doctor will determine the number of ultrasounds recommended for your health and safety.
While ultrasound is considered very safe, additional scans without medical need are not really necessary. Talk to your prenatal care provider about any concerns over too many ultrasounds. They can explain the purpose of each one and put your mind at ease.
Preparing properly for your ultrasounds allows the technician to get optimal images and footage. Follow their instructions for best results. Routine ultrasounds provide valuable information to keep you informed on your baby’s wellbeing up until delivery.