" Oxytocin is an amino acid peptide. A hormone. They call it the love chemical. “So?” Kelsey gave him a dead-eyed stare. “So when you’re further along in your pregnancy, more oxytocin receptors will be created in your uterine muscles. When the baby’s big enough, your oxytocin level will rise, triggering labor, and will help your muscles contract so you can give birth.” “Gross,” said Cory. “No,” Jack said. “Miraculous. Without the oxytocin, your muscles wouldn’t be strong enough to push that baby out. But because of that chemical, you are. You’ll be superhero strong.” He smiled right into Kelsey’s eyes. “Then, when you see your baby, that rush of oxytocin will help you bond. That’s why they call it the love drug. And if you breast-feed, more oxytocin gets released, strengthening that bond. The maternal instinct is the strongest instinct in the world. Chemistry is definitely part of that. "

― Kristan Higgins