"Your baby now weighs about 2 1/2 pounds and is a tad over 15 inches long from head to heel. His muscles and lungs are continuing to mature, and his head is growing bigger to accommodate his brain — which is busy developing billions of neurons. With this rapid growth, it's no surprise that your baby's nutritional needs reach their peak during this trimester. To keep yourself and him well nourished, you'll need plenty of protein, vitamin C, folic acid, iron, and calcium. (About 200 milligrams of calcium is deposited in your baby's skeleton — which is now hardening — every day.)"