女 underneath is the indexing radical, a kneeling-woman pictograph. It places 婴 in the family of woman-and-childbearing words - 妈, 妹, 婚 - and pictures the mother below the strung beads of her newborn.
贝 on the upper-left is one of a pair of cowrie shells. The two shells together depict a string of beads - a baby's necklace, originally hung around a newborn's neck as a charm and ornament.
贝 on the upper-right pairs with its twin on the left to spell out the bead-necklace sense. Two cowries threaded side by side became the visual shorthand for the precious infant adorned with such a string.
