Childbirth is not just some miserable medical procedure. The entire event is a pair bonding activity for the parents and child. Deleting that because it makes you uncomfortable is unwise.
https://www.nichd.nih.gov/health/topics/labor-delivery/topic...
The above list does not even include hemorrhoids that require a hemorrhoidectomy or retained placenta, both which require an operation where the mother has to go under anesthesia.
https://www.cdc.gov/reproductivehealth/maternalinfanthealth/...
Childbirth is remarkably dangerous, even under current medical standards. Even a successful natural birth tends to bring a whole host of complications afterwards, and it's not unreasonable to want to avoid that.
Let me be uncharitable here: do you really think a mom would love her baby any less just because she rip open her entire perineum in the process of pushing that baby out? (If so, I guess I have bad news for C-section babies...)
I'm pointing out that the same phenomenon where "parents" of children born via surrogacy feel less of an attachment to their child would be present in the AWT situation.