Get him a key cut and ask a school mum to drop him off at the door if need be. Exchange phone numbers for just in case. No need to say why. You could be sick for all they know. What I mean is you don't need to tell them why. You won't be going to pick him up post birth. So make sure that the first thing you do if birthing starts is text your emergency contact. Done. Fingers crossed it all starts before morning drop off so DS doesn't have to go to school at all.