I would wait until you have the baby for people to get seats. For one, seats expire, so you don't want to lose 9 months or the seats life.
It sounds like you want an infant seat, so I think before the baby comes, you should get an infant seat and extra base--put one base in your car, one in dad's car. (just assuming dad is in the picture--if not, disregard that one).
Then, I would think about child care. Are you going to have a child care provider? Will the child care provider be transporting your child? If so, I would provide a seat or base. If you have a snugride 35 or something similar, I would purchase the extra base for daycare provider. If you have an infant seat that only goes to 22 pounds, I would probably get a convertible for daycare providers car because it will last longer. Otherwise, you'll have to get a convertible anyway at 9 months so when the baby outgrows the infant seat.
For grandparents--I would wait and see how often they are transporting. My parents got a convertible when my LO was about 6 months because when they watch him, they are extra nice and come pick him up! I didn't want them to get a base because I knew that the convertible would last so much longer. I have a tiny guy (think less than 5% for height) and he outgrow snugride 22 at 9 months.
For anyone else--also wait and see how often you want them transporting. Sometimes it is not too bad to just to install or trade cars.
I am very concerned about anyone else having a seat for my LO that I did not install or check. I installed my parent's seat and showed them how to do it. When they had to take it out for something, I rechecked after they reinstalled it. Also, I make sure people know how to buckle properly. I dislike anyone else driving with my LO unless I buckle him in or I am POSITIVE they will do it properly every time.
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