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.
The sum of these measurements is the amniotic fluid index (AFI). An AFI of 25 centimeters or more indicates polyhydramnios. Your health care provider will also use a detailed ultrasound to diagnose or rule out birth defects and other complications. You may need additional tests as well, including: