Ours was 137 but we also used a lawyer so there were a few additional pages and I think it could have gotten massively cut down had I better organized the photos and their explanations. I got an RFE for my (US citizen's) criminal history since I got some stupid tickets in college. It seemed like a dumb RFE just meant to stall time....
Here is a list of the supporting documentation we gave in addition to the regular 129F paperwork:
Copy of Petitioner's passport (every single page of the passport)
Copy of Petitioner's Birth Certificate
Copy of Beneficiary's Identification
Copy of Beneficiary's Birth Certificate with English translation
Copy of Beneficiary's passport (every single page of the passport, even the blank ones)
Copies of flight itinerary
Copies of boarding passes
Copy of Airbnb receipts from trips together
Copies of photos from our trips (~38 pages of photos and copies of the back with details of when and where)
Letters from Family and Friends attesting to our relationship