Many environmental toxins readily cross the placenta into the baby's circulation.
Sorry.
Well, "I'm" not sorry. I can only speak from experience:
My daughter weighed 8lbs 12 ounces and 21 and a half inches long. She tipped 10 on the newborn baby scale for all things good health.
Even though we drank coffee, smoked, took aspirin and an occasional drink at get togethers, my daughter was born big and healthy. Never had breathing problems, no asthma and the likes of that.
When I was a kid, mother caught me eating dirt. I'm just saying too much protection is not a good thing. Kids need to build up their immune systems. Especially in this day and age when so much junk is floating around in the air.