Wondering if your baby’s weight is normal? Learn the average fetal weight by week from 12 to 40 weeks, how ultrasound estimates fetal weight (EFW), and what normal growth looks like during pregnancy.
Fetal Weight by Week: Is My Baby Growing Normally?
One of the most common questions during pregnancy is:
“Is my baby’s weight normal?”
During routine prenatal ultrasounds, doctors estimate your baby’s weight using several body measurements. This estimate is called Estimated Fetal Weight (EFW).
The table below shows the approximate average fetal weight throughout pregnancy.
Average Fetal Weight by Week
| Gestational Age | Average Weight |
| 12 weeks | 14 g |
| 16 weeks | 100 g |
| 20 weeks | 300 g |
| 24 weeks | 600 g |
| 28 weeks | 1,100 g |
| 30 weeks | 1,400 g |
| 32 weeks | 1,700 g |
| 34 weeks | 2,200 g |
| 36 weeks | 2,700 g |
| 38 weeks | 3,100 g |
| 40 weeks | 3,300~3,500 g |
These values are averages. Every baby grows at a slightly different rate.
How Is Fetal Weight Estimated?
Ultrasound does not measure your baby’s weight directly.
Instead, it calculates an estimate using several fetal measurements, including:
- Biparietal Diameter (BPD)
- Head Circumference (HC)
- Abdominal Circumference (AC)
- Femur Length (FL)
These measurements are entered into validated formulas to calculate the Estimated Fetal Weight (EFW).
How Accurate Is Ultrasound Weight Estimation?
Many parents ask,
“Can ultrasound accurately predict my baby’s weight?”
The answer is mostly yes—but not perfectly.
Ultrasound estimates usually have an error range of ±10–15%.
For example, if the estimated weight is 2,000 g, the actual birth weight may reasonably range from about 1,700 to 2,300 g.
For this reason, healthcare providers focus more on your baby’s growth trend over time than on a single measurement.
What If My Baby Is Smaller Than Average?
A smaller-than-average baby is not always a cause for concern.
Possible reasons include:
- Family genetics
- Naturally small body size
- Normal variation in fetal growth
However, if growth slows significantly or blood flow abnormalities are detected, your doctor may evaluate for Fetal Growth Restriction (FGR/IUGR).
What If My Baby Is Larger Than Average?
A larger baby can also be completely healthy.
Sometimes, increased fetal weight may be associated with:
- Gestational diabetes
- Large for Gestational Age (LGA)
- Delivery planning considerations
Your healthcare provider will assess the overall clinical picture rather than fetal weight alone.
Frequently Asked Questions
Is 1 kg normal at 28 weeks?
Yes. Around 1,100 g is considered average at 28 weeks, so approximately 1 kg is often within the normal range depending on individual growth patterns.
My baby measures two weeks behind. Should I worry?
Not necessarily.
Doctors usually monitor growth over time rather than relying on a single ultrasound measurement.
Is ultrasound weight the same as birth weight?
No.
Estimated Fetal Weight (EFW) is an approximation and may differ from the baby’s actual birth weight.
Final Thoughts
Fetal weight is an important indicator of your baby’s development, but it is only one part of the overall assessment.
Doctors also evaluate fetal anatomy, amniotic fluid, placental function, blood flow, and the baby’s growth pattern over time.
Regular prenatal care and follow-up ultrasounds are the best ways to monitor your baby’s health.
