As a long time breeder here's my checklist of things I do before, during and after breeding, to ensure a healthy foal.
#1 - Make sure the mare is current on all vaccines. Make sure she's cycling and not transitional. Get the mare a cytology, culture and biopsy (at 19 I wouldn't even think of breeding without one)
#2 - if clean, proceed to breed. If not, do the lavage and any treatments the vet tells me to do until she cultures clean.
#3 - if the biopsy comes back 2B or more, know that I have very little chance of getting the mare to carry to term, IF I can get her to settle at all.
#4 - if breeding live cover, I wash her lady parts to make sure she takes nothing to the stallion and wash his manly parts to make sure he doesn't bring anything extra to the party.
#5 - between 17-21 days post breeding (last day bred whether live cover or AI), I have the mare ultrasounded and palpated to check for twinning and to confirm she's ineed in foal.
#6 - 45 days, re-ultrasound and re-palp to confirm she's still in foal.
#7 - 60 days, re-US and Palp to confirm she's still in foal.
#8 - 90 days give the first Rhino vaccine
#9 - 150 days give the 2nd Rhino
#10 - 210 days give the 3rd Rhino
#11 - 270 days give the last Rhino
#12 - 300 days (roughly 1 month before foal is due), give all annual vaccines
#13 - wait for foal to arrive
I have foaling stalls that are set up with cameras and I monitor them 24/7. Considering how much money I spend on just getting the mare in foal, and then to carry her to term, I cannot imagine skipping those beginning ultrasounds. Maybe skip the 60 day one if she's not acting like she's coming back into heat, it's just to make sure things are implanting and going as they should be, but the first 2? NOT on your life, or rather, the foal's life.