Why the Targets Exist
Weight gain funds the fetus, placenta, amniotic fluid, expanded blood volume, and maternal fat stores for breastfeeding. Gaining below target raises risks of small-for-gestational-age babies; gaining above target raises risks of gestational diabetes, hypertension, and delivery complications.
The IOM's 2009 guidelines remain the reference in the U.S., with ACOG endorsing the same bands.
The Weekly Rhythm
Gain is back-loaded. The first trimester contributes little, 0.5–2 kg total, while the second and third add roughly 0.35–0.50 kg per week for normal-BMI women.
Week-to-week fluctuations are normal (fluid, meals, constipation). Providers watch the trajectory across visits, not any single weigh-in.
Tracking Without Obsessing
Weigh once weekly, same conditions, and compare against your BMI band's curve. A slow week or a jump is noise; two consecutive trends off-curve is worth discussing.
If you're above target, the guidance is to slow gain, not to lose, even with obesity, intentional weight loss during pregnancy isn't recommended.
Sources
FAQ
How much weight should I gain in pregnancy?
11.5–16 kg with normal pre-pregnancy BMI; 12.5–18 kg underweight; 7–11.5 kg overweight; 5–9 kg with obesity.
When does most pregnancy weight come?
After week 13, about 0.4 kg per week for normal-BMI women in the second and third trimesters.
Is it safe to lose weight while pregnant?
No, even with obesity the goal is to limit gain to the target band, under your provider's supervision.
A note before you begin: this tool offers educational estimates only. It cannot replace advice from your doctor or another qualified professional.