That's the answer to your description's question: before or on the 51st ball drawn. But since your heading asks a slightly different question, I'll also answer your heading's question, which is just before 51 balls.
Looking for the definition of AFIS? Find out what is the full meaning of AFIS on Abbreviations.com! 'Automated Fingerprint Identification System' is one option -- get in to view more @ The Web's largest and most authoritative acronyms and abbreviations resource.
On our placenta exam requisition sheet, you might find that the L&D providers indicate an abnormal AFI or BPP [L10-9388](a web site). AFI = amnionic fluid index, a measure of the volume. Done by ultrasound, fluid depth is measured in 4 uterine quadrants and the 4 measurements summed.