Healthy weight gain in pregnancy by pre-pregnancy BMI

Why track weight?

Gaining too little or too much can relate to risks such as preterm birth, macrosomia, gestational diabetes, and hypertension. The U.S. Institute of Medicine (IOM), cited by ACOG, gives reference ranges by pre-pregnancy BMI.

What is pre-pregnancy BMI?

BMI = weight (kg) / [height (m)]². The Bầu Ăn Gì? app calculates BMI and offers reference weight-gain guidance when you enter your details.

Reference ranges (singleton pregnancy, IOM/ACOG summary)

• Underweight (BMI <18.5): about 12.5–18 kg (28–40 lb).
• Normal (18.5–24.9): about 11.5–16 kg (25–35 lb).
• Overweight (25–29.9): about 7–11.5 kg (15–25 lb).
• Obesity (≥30): about 5–9 kg (11–20 lb).

Twins or triplets have separate targets — your clinician will advise.

Trimester pattern (estimate)

• First trimester: modest gain (~0.5–2 kg for many).
• Second and third: steadier weekly gain (~0.4–0.5 kg/week depending on BMI).

If weight rises quickly

Focus on quality: more vegetables and lean protein, fewer sugary drinks. Gentle activity if approved (walking, prenatal yoga).

If weight gain is slow

Do not force excess junk food; check nausea, stress, or medical issues. Prenatal visits screen for fetal growth concerns.

Note

These are reference ranges, not rigid rules. Underweight history, edema, or gestational diabetes need individualized plans.