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Pregnancy and health

BMI During Pregnancy: Weight Gain and Interpretation

Standard BMI does not apply during pregnancy. Learn about healthy weight gain.

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Does BMI change during pregnancy?

Yes, completely. During pregnancy, weight naturally and continuously increases due to the growth of the baby, placenta, amniotic fluid, increased blood volume, and maternal fat reserves. That is why the standard BMI is not used to assess the nutritional status of a pregnant woman.

What is used is the pre-pregnancy BMI (the BMI you had before becoming pregnant) to determine how much weight is healthy to gain during the 9 months.

BMI before pregnancyCategoryRecommended weight gain
Less than 18.5Underweight12.5 – 18 kg
18.5 – 24.9Normal11.5 – 16 kg
25 – 29.9Overweight7 – 11.5 kg
30 or moreObesity5 – 9 kg

Why does weight matter during pregnancy?

Gaining too much or too little weight during pregnancy can have consequences for both the mother and the baby.

Risks of gaining too much weight

Risks of gaining too little weight

Distribution of weight gained

In a full-term pregnancy with 12 kg gained: the baby weighs ~3.5 kg, placenta ~0.7 kg, amniotic fluid ~0.8 kg, uterus growth ~0.9 kg, increased blood volume ~1.5 kg, extracellular fluid ~1.5 kg, maternal fat ~3.5 kg.

Important: All nutritional guidance during pregnancy must be personalized by your obstetrician or nutritionist. This information is for general guidance only.

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