Third Trimester Growth Scan Guide

It’s totally normal to feel a bit curious or even a little unsure about your baby’s development, especially when you reach the final stretch of pregnancy. The third trimester growth scan is a common checkup, but for many, it can bring up questions about what it is and why it’s done. Don’t worry, we’ll break it all down for you simply and clearly, step-by-step.

What you’ll learn next will help you feel prepared and informed about this important part of your pregnancy.

Key Takeaways

Understand the purpose of a third trimester growth scan.
Learn what the scan measures and why it’s important for baby’s health.
Discover when and why this scan is typically recommended.
Know what to expect during the appointment itself.
Understand how the results are interpreted and what they mean for you.

Why A Third Trimester Growth Scan Is Important

During the last few months of pregnancy, your baby grows a lot. A third trimester growth scan helps doctors make sure your baby is growing just right. It’s like a check-up to see if everything is on track for a healthy arrival.

This scan looks at various things to get a good picture of how your baby is developing and if they are getting everything they need inside the womb.

What Does a Growth Scan Measure

A growth scan looks at several key measurements to estimate your baby’s size and weight. It checks the baby’s head circumference, the abdomen, and the femur, which is the thigh bone. These measurements are used with special formulas to calculate an estimated fetal weight.

Head Circumference (HC): This measurement helps assess brain development and overall head size. It is taken at the widest part of the baby’s head, just above the ears. A consistent growth in head circumference suggests healthy brain development. Deviations might prompt further investigation to ensure normal development.
Abdominal Circumference (AC): This measures the baby’s belly and gives an idea of how well the baby is nourished. The size of the abdomen is closely linked to the baby’s weight and how much fat they are storing. It’s a critical indicator of the baby’s nutritional status and liver size.
Femur Length (FL): This is the length of the baby’s thigh bone. It’s a good indicator of skeletal growth. The femur usually grows at a steady rate throughout pregnancy, and its length contributes to the overall estimation of fetal size.
Estimated Fetal Weight (EFW): This is calculated using the HC, AC, and FL measurements. It gives a good idea of how much your baby weighs. Doctors use this to see if the baby is growing within the expected range for their gestational age.

Assessing Amniotic Fluid Levels

Besides measuring the baby, the scan also checks the amount of amniotic fluid around the baby. This fluid is important because it protects the baby and helps their lungs develop. The scan will measure the deepest pocket of fluid.

This measurement helps doctors understand if there’s too much or too little fluid, which can sometimes indicate a problem.

Amniotic Fluid Index (AFI): This is a common way to measure amniotic fluid. The sonographer divides the uterus into four quadrants and measures the deepest pocket of fluid in each. These measurements are added together to get the AFI. A normal AFI is usually between 5 and 25 cm.
Deepest Vertical Pocket (DVP): Some doctors prefer to measure just the deepest single pocket of amniotic fluid. A normal DVP is typically between 2 and 8 cm. Both AFI and DVP help assess the baby’s well-being.

Placental Health Assessment

The placenta is the baby’s lifeline, providing oxygen and nutrients. The growth scan looks at the placenta’s position, thickness, and appearance. A healthy placenta is vital for a healthy pregnancy.

If the placenta doesn’t seem to be working well, it can affect the baby’s growth.

Placental Position: The scan checks if the placenta is attached to the uterine wall properly. It also checks if it is covering the cervix, which is known as placenta previa, a condition that may require special care.
Placental Grading: The placenta is graded from 0 to 3 based on its maturity. A grade 0 placenta is very early in pregnancy, while a grade 3 placenta is more mature and often seen closer to the due date. This grading helps assess how well the placenta is functioning.
Placental Blood Flow Doppler Studies: In some cases, doctors might use Doppler ultrasound to check the blood flow between the placenta, the baby, and the mother. This can reveal if the placenta is providing enough oxygen and nutrients.

When Is A Third Trimester Growth Scan Recommended

While not every pregnant person needs a growth scan, they are often recommended in specific situations to ensure the baby is developing as expected. These scans are typically performed from around 28 weeks of pregnancy onwards. Doctors consider several factors when deciding if a growth scan is necessary.

Common Reasons for Recommendation

Doctors often suggest a growth scan if they have concerns about the baby’s growth based on regular check-ups or previous scans. This can include if the mother’s belly seems larger or smaller than expected for the stage of pregnancy. It’s a way to get more detailed information and peace of mind.

Concerns About Baby’s Size: If the fundal height (the measurement from the pubic bone to the top of the uterus) is significantly larger or smaller than expected for the gestational age, a growth scan may be ordered. This can indicate potential issues like macrosomia (baby being larger than average) or intrauterine growth restriction (IUGR), where the baby is not growing as expected.
Maternal Health Conditions: Certain health conditions in the mother can affect fetal growth. These include diabetes, high blood pressure (preeclampsia), kidney disease, or heart conditions. These conditions can alter the flow of nutrients and oxygen to the baby, making monitoring via growth scans important.
Previous Pregnancy History: If a mother has a history of delivering a baby with growth problems, either too small or too large, a growth scan in a subsequent pregnancy can help monitor for similar issues. It allows for early detection and management if needed.
Multiple Pregnancies: In cases of twins, triplets, or more, monitoring fetal growth is crucial because the babies share the uterine space and resources. One twin might grow slower than the other, or both might be affected differently. Growth scans help assess each baby’s development individually.

What To Expect During The Scan

The third trimester growth scan is very similar to other ultrasounds you may have had during your pregnancy. It uses sound waves to create images of your baby. You’ll lie down, and a technician will apply a cool gel to your belly.

Then, they will move a handheld device, called a transducer, over your abdomen to get the images.

The Procedure: The scan is typically painless and non-invasive. The gel helps the transducer make good contact with your skin, allowing clear sound waves to travel to your baby and bounce back. You will likely see a black and white image of your baby on a screen. Some clinics allow partners or family members to be present during the scan.
Duration: A standard growth scan usually takes about 20 to 45 minutes. The time can vary depending on how easily the sonographer can get clear images of the baby and whether any specific concerns need to be investigated further. If the baby is not in a good position, it might take a bit longer to get all the necessary measurements.
What You Will See: You’ll see images of your baby, which might include their face, hands, feet, and the internal organs. The sonographer will point out different parts of your baby and take various measurements. It’s a good opportunity to see your baby moving and growing in the final stages of pregnancy.

Interpreting The Results

Once the scan is complete, the sonographer or doctor will review the measurements. They will compare your baby’s estimated size and weight to the averages for babies at the same stage of pregnancy. This helps determine if your baby is growing appropriately.

Understanding Estimated Fetal Weight

The estimated fetal weight (EFW) is a key number from the scan. It provides a range within which your baby’s weight is likely to fall. Doctors use this to see if the baby is on track.

It’s important to remember that this is an estimate, and the actual birth weight can differ slightly.

Percentiles: Fetal growth is often described using percentiles. For example, a baby in the 50th percentile is average in size, meaning they are bigger than 50% of babies and smaller than 50% of babies at the same gestational age. A baby in the 10th percentile is smaller than 90% of babies, while a baby in the 90th percentile is larger than 90% of babies.
Small for Gestational Age (SGA): If a baby’s estimated weight falls below the 10th percentile, they are considered small for gestational age. This doesn’t automatically mean there’s a problem, but it warrants further monitoring to understand why. It could be genetic, due to placental issues, or maternal health.
Large for Gestational Age (LGA): Conversely, if a baby’s estimated weight is above the 90th percentile, they are considered large for gestational age. This can sometimes be related to maternal diabetes or genetics. It might influence decisions about delivery, such as planning for a C-section if the baby is exceptionally large.

What If Growth Is Not As Expected

If the scan shows that your baby’s growth is slower or faster than expected, your doctor will discuss this with you. They may recommend more frequent scans or additional tests to understand the reason and ensure your baby’s well-being. Sometimes, adjustments to your diet or lifestyle might be suggested.

Monitoring and Further Scans: If growth is a concern, your healthcare provider will likely schedule follow-up scans every few weeks. These scans help track the baby’s progress and see if the growth pattern changes. This consistent monitoring is key to managing any issues.
Delivery Timing and Method: In some cases, if the baby is not growing well or if there are concerns about their health in the womb, doctors might suggest delivering the baby a little earlier. They will weigh the risks and benefits carefully. The method of delivery, whether vaginal or C-section, might also be influenced by the baby’s size and the overall situation.
Lifestyle Adjustments: For some conditions, like mild IUGR, simple lifestyle changes might be recommended. This could involve ensuring you are eating a balanced diet, getting enough rest, and avoiding certain activities. Your doctor will provide specific advice based on your situation.

Common Myths Debunked

Myth 1: Growth scans are always 100% accurate in predicting birth weight.

The reality is that growth scans provide an estimated fetal weight, which is a range. Factors like the baby’s position, the amount of amniotic fluid, and the sonographer’s skill can influence accuracy. While they are very useful tools, actual birth weights can sometimes differ from the estimated weight by up to 10-15%.

Myth 2: If my baby is measuring small, there’s definitely something wrong.

Not necessarily. Some babies are naturally smaller, just like some adults are. If a baby measures small, doctors will investigate to rule out any underlying issues.

However, many babies who measure small are perfectly healthy and catch up in growth after birth. It’s about understanding the individual baby’s growth pattern.

Myth 3: Growth scans are the same as regular anatomy scans.

While both are ultrasounds, they have different primary goals. An anatomy scan, usually done around 20 weeks, focuses on checking the baby’s physical development and looking for any structural abnormalities. A third trimester growth scan, however, specifically focuses on the baby’s size, weight, and rate of growth, as well as assessing the amniotic fluid and placenta.

Myth 4: You only need a growth scan if you’re having complications.

While growth scans are often recommended for high-risk pregnancies, they can also be performed for low-risk pregnancies if the doctor has a specific question or concern, or sometimes as part of routine care in certain regions or hospitals. It’s a tool to provide extra information when it’s deemed beneficial.

Frequently Asked Questions

Question: How often are third trimester growth scans done?

Answer: The frequency of growth scans varies. If there are no concerns, you might only have one or none. If there are concerns, they might be done every 2-4 weeks.

Question: Can I request a growth scan?

Answer: You can discuss your concerns with your doctor. They will decide if a growth scan is medically indicated based on your pregnancy.

Question: Is the gel used for the scan harmful to the baby?

Answer: No, the ultrasound gel is water-based and completely safe. It is used to help the transducer transmit sound waves effectively.

Question: Will the scan tell me the baby’s sex?

Answer: A growth scan can sometimes show the baby’s sex if the baby is in a good position and you haven’t found out already. However, its main purpose is to assess growth, not to determine sex.

Question: What happens if my baby is measuring very large?

Answer: If your baby is measuring large, your doctor will discuss the implications, which might include further monitoring or planning for delivery. It can sometimes mean a higher chance of needing a C-section.

Summary

The third trimester growth scan is a valuable tool. It helps healthcare providers monitor your baby’s development in the final weeks. By checking size, weight, amniotic fluid, and placental health, doctors ensure your baby is growing well.

This scan offers reassurance and allows for timely intervention if any issues arise, supporting a healthy outcome for you and your baby.