Saline (Fleet) enemas in first trimester

If you Google if enemas are safe in the first trimester, you’ll see a resounding “no”, saying they can trigger a miscarriage. However, not one single article or post on any forum ever links to any sort of study or explanation as to why this may happen. A saline enema works similarly to other things considered safe like Miralax by pulling water into the colon, except with a Fleet enema, it’s localized and therefore more immediate. Furthermore, I found several established OBGYN clinics that say saline Fleet enemas are safe. The sites that say it’s not never distinguish between the various types of enemas that I could see being unsafe, such as those that contain drugs or compounds that actively stimulate the bowels rather than just loosening things up with some saline water. This is not meant to convince people they are safe, but only to ask if anyone has ever seen any sort of explanation. My wife is 9 weeks pregnant and has horrible constipation, sometimes not being able to go for several days at a time. She’s tried everything else and has resorted to one enema about once every week or two so she can get some relief. Last night she came home looking 6 months pregnant from the severe bloat. People at her work even commented on it. Anyway, I would appreciate any further safety information that I wasn’t able to find.