IOM 2009 guidelines for twin pregnancy weight gain by pre-pregnancy BMI: Underweight (BMI <18.5): 50-62 lbs, Normal weight (BMI 18.5-24.9): 37-54 lbs, Overweight (BMI 25-29.9): 31-50 lbs, Obese (BMI ≥30): 25-42 lbs.

Higher than singleton pregnancy (25-35 lbs normal BMI).

Most gain occurs in 2nd/3rd trimester.

Inadequate gain increases preterm birth risk, excessive gain increases gestational diabetes and C-section risk.

Twin pregnancy nutritional requirements: Calories: +600 per day above baseline (vs +300 for singleton).

Example: 2,000 baseline + 600 = 2,600 calories/day.

Protein: 150-175g daily (vs 71g singleton), 25-30g per meal.

Folic acid: 1,000 mcg (vs 600 mcg singleton).

Iron: 60-100 mg (vs 27 mg).

DHA: 300-600 mg omega-3.

Calcium: 1,200-1,500 mg.

Eat nutrient-dense foods - twins deplete maternal reserves faster.

Twin types affect pregnancy monitoring: Monochorionic (identical, share placenta): 1/3 of twins, higher risk TTTS (twin-to-twin transfusion syndrome), more frequent ultrasounds every 2 weeks, closer weight gain monitoring.

Dichorionic (fraternal or identical, separate placentas): 2/3 of twins, lower complication risk, ultrasounds every 4 weeks, standard twin weight gain applies.

Chorionicity determined by early ultrasound (6-14 weeks).

Affects delivery timing and monitoring intensity.

Inadequate gain (<37 lbs normal BMI): Preterm birth before 37 weeks (60% risk vs 12% singleton), Low birth weight babies (<5.5 lbs each), NICU admission, developmental delays.

Excessive gain (>54 lbs normal BMI): Gestational diabetes (8-10% vs 5% singleton), Preeclampsia (10-20% vs 5%), C-section delivery (75% vs 32% singleton), Postpartum weight retention.

Target steady gain: 1-1.5 lbs/week in 2nd/3rd trimester.

Twin pregnancy weight gain accelerates earlier: 1st trimester (weeks 1-13): 5-10 lbs total (vs 2-4 singleton), 2nd trimester (weeks 14-27): 1.5 lbs/week (vs 1 lb singleton), 3rd trimester (weeks 28-37): 1 lb/week (vs 1 lb singleton, but twins deliver earlier).

Total duration: 35-37 weeks average twin delivery vs 40 weeks singleton.

More rapid early gain needed - twins have higher metabolic demands from conception.

Weekly weight checks recommended after 20 weeks.

NO - weight restriction during twin pregnancy is dangerous.

Even obese mothers (BMI 30+) should gain 25-42 lbs minimum for twin health.

Risks of dieting: Severe intrauterine growth restriction, Preterm labor (twins already 60% risk), Nutrient deficiencies affecting brain development, Placental insufficiency.

Focus on quality nutrition, not restriction.

Acceptable: Avoid empty calories (soda, candy), moderate portions, gentle exercise (walking, swimming).

Consult maternal-fetal medicine specialist for personalized plan if BMI >35.