There's the birds and the bees. And then there's what happens after. The process that leads to the beginning of pregnancy has a lot more twists and turns than a happenstance meeting. Today on Short Wave, NPR health reporter Selena Simmons-Duffin talks about the science of the very first week of pregnancy.Read Selena's full explainer by clicking this link. Or download and print it here. Have an incredible science story to share? Email us at shortwave@npr.org.