• Counseling patients on optimal, evidence-based weight gain during a singleton or twin pregnancy.
• Mitigating risks of macrosomia, cesarean delivery, and childhood obesity associated with excessive weight gain.
• Preventing low birth weight and preterm delivery associated with inadequate weight gain.

• For severely obese women (Class III, BMI > 40), many modern specialists actually recommend ZERO weight gain or even safe, physician-supervised minor weight loss during pregnancy, as it paradoxically lowers their risk of preeclampsia without harming the fetus.
• Do not scold patients for sudden 5 lb weight leaps at 36 weeks; this is almost entirely third-trimester fluid retention (edema) or amniotic fluid, not adipose gain.

• If blowing past the threshold early: Screen aggressively for early-onset Gestational Diabetes and refer to a dietician immediately. Emphasize that excess weight is highly resistant to postpartum loss.
• If failing to gain weight: Investigate hyperemesis gravidarum, severe food insecurity, or eating disorders. Check a fetal growth ultrasound to ensure the fetus isn't suffering from Fetal Growth Restriction (FGR).

In the 1950s, doctors restricted women to gaining no more than 15 lbs to keep babies small and deliveries easy, which led to a crisis of neurodevelopmental delays and cerebral palsy from starving fetuses. The pendulum swung too far in the 1990s ("eat whatever you want"), creating the modern maternal obesity crisis. The 2009 IOM guidelines finally struck the perfect, evidence-based middle ground.