If you’re expecting, especially after IVF, you’ve likely been through multiple ultrasounds, blood tests, and scans. Among them, the third-trimester growth scan is one of the most closely watched. One key number from this scan often causes anxiety: the estimated fetal weight (EFW). But how accurate is a growth scan in predicting your baby’s actual birth weight?
Why IVF Pregnancies Require Stricter Fetal Growth Tracking
Women who conceive through IVF are more likely to undergo frequent growth scans, and for good reason. IVF pregnancies carry a higher likelihood of multiple gestation, which naturally increases the need for close monitoring. There’s also an elevated risk of Intrauterine Growth Restriction (IUGR), especially in cases involving embryo manipulation or underlying fertility issues. Many IVF mothers are also over the age of 35, which adds age-related risks to the pregnancy. Additionally, IVF pregnancies are more prone to complications like placenta previa or gestational diabetes, both of which can impact fetal growth. Because these factors can influence how well the baby is developing, doctors often rely on serial growth scans to track changes, ensure the fetus is thriving, and make timely decisions, particularly when it comes to the safest time and mode of delivery.
How Accurate Are Growth Scan Reports for Baby’s Weight?
Growth scans rely on biometric data like Biparietal Diameter (BPD), Femur Length (FL), Abdominal Circumference (AC), and Head Circumference (HC) to estimate fetal weight, but it’s important to remember this isn’t an exact science. The accuracy of these estimates ranges between 70–85%, meaning a baby estimated to weigh 2.8 kg could weigh anywhere from 2.4 to 3.2 kg at birth. Certain factors, such as maternal obesity, baby’s position, or low amniotic fluid levels, can also affect the precision of these measurements. In IVF pregnancies, it’s common to see slightly smaller biometric values in the third trimester, but these often catch up by delivery and aren’t always a cause for concern. Despite its limitations, the Estimated Fetal Weight (EFW) provides doctors with a valuable baseline to track growth trends over time, and in many cases,
these trends matter more than a single isolated number.
Why Serial Scans Matter More Than One-Time Estimates
It’s not just about one scan; serial growth tracking is key to understanding your baby’s development. Growth scans done at 28, 32, and 36 weeks provide a more accurate picture of how your baby is progressing over time, rather than relying on a single measurement. For instance, a baby consistently growing along the 25th percentile is usually less concerning than one who drops from the 50th to the 10th percentile in just a couple of weeks. These trends help identify potential issues early, such as growth restriction or placental insufficiency. Tracking how different parameters, like head vs. abdominal growth, change concerning each other can also reveal asymmetries that may point to underlying problems with nutrition or blood flow from the placenta. This longitudinal approach helps doctors make better-informed decisions about monitoring and delivery.
Red Flags That Require Closer Monitoring
Doctors may investigate further if:
- There’s a slowed growth velocity between the two scans
- EFW falls below the 10th percentile
- There’s abnormal blood flow in the umbilical artery (Doppler test)
- There’s discordance in twin or multiple pregnancies
Growth Scans and IVF
In IVF pregnancies, doctors often take a more comprehensive approach by combining growth scans with additional monitoring tools to ensure both mother and baby stay healthy. Doppler studies are commonly used to assess placental blood flow, helping detect any early signs of insufficiency. Cervical length scans can monitor the risk of preterm labor, especially important in cases of multiple gestation or a history of miscarriage. As the pregnancy progresses, non-stress tests (NSTs) are often done more frequently in the third trimester to check on fetal well-being. These extra precautions are designed to manage the higher risk profile of IVF pregnancies, not to create anxiety, but to catch and address any concerns early, offering the best chance for a safe and successful delivery.
Schedule Your IVF Fetal Growth Tracking Plan at Milann
At Milann, our fetal medicine and IVF teams work hand-in-hand to tailor growth tracking for every pregnancy. Whether you’re 28 weeks or nearing your due date, we’ll make sure no detail is missed.
Book your next fetal growth scan with us and take the guesswork out of your journey to parenthood.
Reviewed by
Dr. Kavya D Sharma - Consultant - Reproductive Medicine, Whitefield.
