Did you know? A baby is born every 8 seconds in the U.S.? The average age of first-time mommies: 24.6 years. On average, women gain 30.5 pounds during pregnancy. The average birth weight: 7.7 pounds The average length: 20 inches. After hospital bills, baby expenses for the first year average $8,000 to $10,000. New parents will change 2,200 diapers the first year! Babies aren't born with kneecaps! They develop later. Who knew?