Pregnancy dramatically increases nutritional demands. What a mother eats profoundly affects fetal development, pregnancy outcomes, and even the child's long-term health.

Critical nutrients during pregnancy:

• Folate (B9) — 400–800 mcg/day. Essential in first trimester. Prevents neural tube defects (spina bifida). Start before conception.
• Iron — demand doubles. Needed for fetal blood development and to prevent maternal anemia.
• Iodine — critical for fetal thyroid and brain development
• DHA (omega-3) — fetal brain and eye development
• Calcium — fetal skeleton. If intake is inadequate, fetus draws from maternal bones.
• Vitamin D — deficiency increases risk of gestational diabetes, preeclampsia

What to avoid: Raw fish (mercury), undercooked meat (listeria), unpasteurized products, alcohol, high-dose vitamin A supplements.

Weight gain: IOM guidelines recommend 25–35 lbs for normal BMI pregnancies.

Reference:

Wikipedia: Nutrition and pregnancy

https://en.wikipedia.org/wiki/Nutrition_and_pregnancy