As soon as we find out we’re pregnant, it’s perfectly normal to be super curious and concerned about the size and weight of the fetus during pregnancy, always wanting to make sure everything’s okay at every prenatal visit and ultrasound. Watching the baby’s weekly growth happen at the right pace and monitoring the head circumference measurements is wonderful. Now, having a fetal weight chart to help you track this development is even better.
| Week | Size Head to Bottom | Weight |
| 8 | 1.6 cm | 1 gram |
| 9 | 2.3 cm | 2 grams |
| 10 | 3.1 cm | 4 grams |
| 11 | 4.1 cm | 7 grams |
| 12 | 5.4 cm | 14 grams |
| 13 | 7.4 cm | 23 grams |
| 14 | 8.7 cm | 43 grams |
| 15 | 10.1 cm | 70 grams |
| 16 | 11.6 cm | 100 grams |
| 17 | 13.0 cm | 140 grams |
| 18 | 14.2 cm | 190 grams |
| 19 | 15.3 cm | 240 grams |
| 20 | 16.4 cm | 300 grams |
| Week | Size Head to Toe | Weight |
| 21 | 26.7 cm | 360 grams |
| 22 | 27.8 cm | 430 grams |
| 23 | 28.9 cm | 501 grams |
| 24 | 30.0 cm | 600 grams |
| 25 | 34.6 cm | 660 grams |
| 26 | 35.6 cm | 760 grams |
| 27 | 36.6 cm | 875 grams |
| 28 | 37.6 cm | 1005 grams |
| 29 | 38.6 cm | 1153 grams |
| 30 | 39.9 cm | 1319 grams |
| 31 | 41.1 cm | 1502 grams |
| 32 | 42.4 cm | 1702 grams |
| 33 | 43.7 cm | 1918 grams |
| 34 | 45.0 cm | 2146 grams |
| 35 | 46.2 cm | 2383 grams |
| 36 | 47.4 cm | 2622 grams |
| 37 | 48.6 cm | 2859 grams |
| 38 | 49.8 cm | 3083 grams |
| 39 | 50.7 cm | 3288 grams |
| 40 | 51.2 cm | 3462 grams |
| 41 | 51.7 cm | 3597 grams |
| 42 | 51.5 cm | 3685 grams |
| 43 | 51.3 cm | 3717 grams |
It’s important to remember that every baby develops according to the mother’s health, and also depends on genetic factors like the parents’ weight and height. The compatibility of these factors is essential at the time of the ultrasound, to find out if the baby’s weight during pregnancy is in line with what’s expected.
The fetal weight chart values serve as a guideline but shouldn’t be taken too literally. It’s up to the doctor to determine whether the baby’s weekly growth is on track for the parents’ body type and for the gestational age.
IMPORTANT: Women with diabetes, obesity, prolonged pregnancy, or advanced maternal age are at risk for having babies larger than what is considered normal.
If your baby is larger than the average measurements for gestational age on the fetal weight chart, it’s important to consider glucose testing to rule out the possibility of gestational diabetes. On the other hand, if your baby is smaller than the average for gestational age, a study should be done to check whether the placental blood flow to the fetus is meeting all of the baby’s needs.
How to Calculate the Size of the Fetus
Here’s how to calculate fetal weight to help expecting moms monitor their baby’s weight. This is the method I used in all three of my pregnancies, and it can help satisfy a bit of curiosity. Remember that every baby is unique and should be evaluated individually. So don’t worry if the numbers aren’t exactly the same as your baby’s measurements. To calculate your baby’s size, you should multiply the femur length by 7.
That way, you’ll know the approximate size of your baby. If the measurement is 2.3 cm, for example, then 2.3 cm x 7 = 16.1 cm, so your baby is about 16 centimeters long. In the early stage, the size can be measured from head to bottom. Later, the baby grows and the size and weight during pregnancy can only be measured in parts, which is why this multiplication method is used.
Readers’ Questions:
How Can I Increase the Fetus’s Weight During Pregnancy?
If an ultrasound shows that the fetus is underweight, the obstetrician may recommend adding some foods to the diet that help with weight gain, particularly those rich in protein. Another option is certain vitamin supplements. However, you should only use these supplements if recommended and supervised by a doctor.
How Can I Know if the Fetus’s Weight Is Normal?
Only a physician specializing in ultrasound can examine and determine from the fetal measurements and images taken during the exam whether the fetus’s weight is within the expected range for gestational age. The exam report will contain all the information for the obstetrician to review at your prenatal appointment.
What Influences the Weight of the Fetus?
The weight of the fetus is directly related to the mother’s nutrition and pregnancy health. It’s not a matter of “eating for two,” but rather investing in a healthy diet1, following a menu rich in vitamins like omega 3, folic acid, vitamins A and C, and minerals such as iron, calcium, phosphorus, and zinc. Keep in mind that prenatal multivitamins should be used from the beginning of pregnancy, at the start of prenatal care, since it’s practically impossible to get all these vitamins in the necessary daily amounts from food alone2.
These multivitamins are complete, with iron, folic acid, and all the other vitamins that are vitally important for fetal development. The vitamins contained in multivitamins are very important—not only do they nourish, but they can also prevent possible malformations in the baby. Finally, problems with the placenta can also impact the fetus’s weight and should be investigated with care.
Also see: Head Circumference: Table of Baby’s Head Size During Pregnancy
