It’s a big concern for most pregnant women – wanting to know if their baby is growing and developing properly. You eagerly await each visit to the doctor and ultrasound examination so you can hear that everything is OK with your baby. Additionally, watching the growth occur right before your very eyes is truly a delight.

Using this chart to track weight and length of your baby can help you put your mind at ease and know that everything is going well.

Week Size – head to bum Weight
8 1,6 cm 1 gram
9 2,3 cm 2 gram
10 3,1 cm 4 gram
11 4,1 cm 7 gram
12 5,4 cm 14 gram
13 7,4 cm 23 gram
14 8,7 cm 43 gram
15 10,1 cm 70 gram
16 11,6 cm 100 gram
17 13,0 cm 140 gram
18 14,2 cm 190 gram
19 15,3 cm 240 gram
20 16,4 cm 300 gram
Week Size – head to bum Weight
21 26,7 cm 360 gram
22 27,8 cm 430 gram
23 28,9 cm 501 gram
24 30,0 cm 600 gram
25 34,6 cm 660 gram
26 35,6 cm 760 gram
27 36,6 cm 875 gram
28 37,6 cm 1005 gram
29 38,6 cm 1153 gram
30 39,9 cm 1319 gram
31 41,1 cm 1502 gram
32 42,4 cm 1702 gram
33 43,7 cm 1918 gram
34 45,0 cm 2146 gram
35 46,2 cm 2383 gram
36 47,4 cm 2622 gram
37 48,6 cm 2859 gram
38 49,8 cm 3083 gram
39 50,7 cm 3288 gram
40 51,2 cm 3462 gram
41 51,7 cm 3597 gram
42 51,5 cm 3685 gram
43 51,3 cm 3717 gram

It’s important to remember that these measurements are just a guideline. Each baby develops differently, according to a number of influences. Genetic factors, such as the weight and height of both the parents definitely play a part. Additionally, the health of the mother will impact fetal growth.

Your doctor will take all of these into account when looking at the ultrasound and working out the measurements of your baby. They will them use the information to decide if the baby’s growth week-to-week is acceptable according to parental biology and gestational age.

IMPORTANT: Women suffering from diabetes, obesity, a prolonged pregnancy, or advanced maternal age are likely to be carrying babies that larger than normal.

If you find that your baby is larger than the average measurements for its gestational age, you’ll likely be encouraged to do a blood glucose test by your doctor. This will be to check for gestational diabetes.

If, on the other hand, your baby is actually smaller than it should be for its gestational age, your doctor will test the placenta. It’s possible that the placenta isn’t supplying the fetus with all of the nutrients it needs to grow and develop properly.

How to calculate the size of the fetus

Using this table will help you to work out how much your baby weighs and how big it is likely to be when it’s born. Remember, this table is based on averages and it doesn’t matter if your baby isn’t exactly the same as the measurements shown. Your doctor will help you with working out why there is a difference and if there is any cause for concern.

When your baby is still small and can be seen all in one go on the ultrasound, the doctor will give you a full measurement from head to bum. However, once your baby starts to grow and the ultrasound can no longer pick up the entire area in one image, the measurements will be taken in sections. In order to calculate the approximate size of your baby from these measurements, multiply the length of its femur by 7.

Readers’ questions:

How do I increase the weight of my baby while I’m still pregnant?

It’s important to get advice directly from your doctor as they will know your medical history. If your baby is shown to be underweight during an ultrasound, your obstetrician may well suggest certain foods that are high in protein that you should try eating and prescribe specific vitamins that should help.

How do I know if the fetal weight is normal?

Only your gynecologist will be able to answer this question. They will do regular ultrasound scans to examine the size of the fetus and monitor you to ensure that everything is progressing normally, and that your baby is at an acceptable weight for its gestational age.

What influences the weight of my unborn baby?

The weight of the fetus is directly linked to maternal nutrition and gestational health. The old adage ‘eating for two’ isn’t completely accurate, but you do need to increase your food intake when pregnant. It’s important, however, to increase your intake of the right kind of foods. Your diet should include things that are rich in omega 3 fatty acids, folic acid, vitamins A and C, iron, calcium, phosphorus and zinc.

If your diet is good but your baby is still underweight, there may be a problem with the placenta. Your doctor will test for this and provide a suitable course of action if this is the case.