BMI in pregnancy

Why BMI is part of prenatal care

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).

Healthy weight gain differs for each person; track it with your prenatal doctor.

Note

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