Maternal nutrition directly supports fetal growth because all the nutrients the fetus needs come from the mother's intake. The placenta transfers energy-yielding nutrients like glucose and amino acids, as well as vitamins and minerals, from what the mother eats into the developing baby. When a mother has adequate energy and protein, along with sufficient micronutrients, fetal tissues and organs can grow properly, contributing to a healthy birth weight. Conversely, inadequate intake or insufficient weight gain during pregnancy often leads to low birth weight, while excessive intake can be associated with heavier babies and potential complications. Paternal nutrition doesn’t directly supply the fetus with nutrients, so it does not determine birth weight in the same way maternal intake does. Fat intake of the mother is a part of overall nutrition, but birth weight is influenced by the total quality and amount of nutrients—not just fat. Physical activity has important health benefits for the mother and pregnancy, but it isn’t the primary determinant of birth weight, which is largely driven by what the mother consumes and how that supports fetal growth.