Bottom line: In American English, the most correct and generally accepted pronunciation of Latin words ending in -ae appears to be the long ē sound, as in “tea” or “Caesar salad.”
I had an anatomy professor at New Mexico State University that was absolutely adamant that the terminal “ae” sound, as in “placentae,” should be pronounced with the long ē sound: “placentee.” He really harped on this, over and over, insisting that people pronouncing it with the diphthong (as in “say”) were outright wrong. I grew accustomed to his recommended pronunciation, but over the course of medical school I’ve rarely heard it. Instead, each professor, attending, resident, and student seems to have his or her own, uniquely awkward way of pronouncing words like “uvulae.”
Tonight, my roommate and I did a few minutes of investigation, and it seems like my old professor was correct for the most part. For example, here is the Oxford Dictionary page for placentae. It seems that the “ee” sound is correct for the American English pronunciation, at least. If you’re speaking Latin, you may go for the traditional pronunciation, something sounding more like “eye” (e.g. the Oxford entry for uvulae, which shows both). Not much support for the clumsy “hey” sound.
Here’s a great site with soundclips from the UNC Greensboro Department of Classical Studies, which suggests the traditional pronunciation for curriculum vitae (phonetically something like curriculum vee-tie), but clearly demonstrates the “Standard American pronunciation” of alumnae as the phonetic equivalent of “alum-knee.”
Along the way, we encountered a number of lively debates regarding the three plural forms of cactus, platypus, Greek vs Latin roots, and numerous examples of “placentas,” “cervixes,” and “appendixes” being just as correct as “placentae,” “cervices,” and “appendices.” In other words (ha), there’s plenty of opinion to go around, and as a medical student or resident there will never be a shortage of people telling me I’m wrong, but it seems that my old anatomy professor was right. In American English, no other pronunciation of -ae seems more correct or widely accepted than the long ē. Some reputable sources list it as the preferred pronunciation. Although I admit this could just be coincidental, my roomie came up with what seems to be an excellent example: Caesar salad.
So next time you’re stumbling over “fimbriae” (pronunciation at Merriam-Webster), remember: there’s no need for awkward diphthong slurs, just give it an “ee.”