I can't really offer a scientific/logic-based approach to this, since there is no predicting your baby's 1st or 2nd year (or complications with pregnancy/delivery/etc) in most cases...
What I can say is that for us, we had the cadillac plan for #1, nothing OOP at all besides the cost of payroll deduction for the insurance plan itself, for pregnancy & birth. Easy birth with midwives at a hospital. Typical 2-day stay for mother & baby. All preventative care visits were covered by our insurance in full (vaccinations, well baby check-ups every few months). We did not have any ER visits. Super cheap prescriptions, but only needed one for baby's first year. Not a deciding factor for us.
#2, we had the equivalent of a Honda Civic plan (HMO, standard coverage, about 30% less cost in monthly premiums than the Cadillac plan above) - $200 per admission to L&D (we only had the one, while in real labor), uncomplicated pregnancy, covered at $0 OOP for all Dr. Visits, ultrasounds, even the high-risk Dr. visits for a few issues. Free breastpump & milk bags every 90 days (thanks ACA!) Easy birth. Fully covered. Two-day stay, nobody was sick. All preventative care visits were covered by insurance in full, no ER visits. Probably 2 sick baby visits, had to pay $20 copay each time I think. Our insurance coverage is good, but not as good as it was with the cadillac plan above for #1, but luckily only needed antibiotics one time ($10) and some cream another time ($20 i think?)
Since it's hard to plan for the unknown, I would go with the coverage you feel most comfortable with. All totaled, each birth was easily $15k with dr. bills, hospital bills, anesthesiologist, etc. I would not have felt comfortable with HSA/HDHP only, in the event of some catastrophic event (heart defect discovered after birth, a long stay in the NICU, etc). And after the birth of the baby (or even during, as your mind is adding up the $$$$$ of each specialist that comes in your room) is NOT the time to worry about how you're going to pay for the birth of a child. It's a happy time... should be spent focused on baby and mom and dad as a family unit. Some things are worth paying slightly more for, (temporarily since you can always switch back to the HSA/HDHP after baby arrives) so that you can have peace of mind. Good luck!