Most of the fluid in amniotic fluid is contributed to by fetal urine. This is then reabsorbed by the membranes and umbilical cord and the turnover is pretty fast— a couple of hours. So it’s possible to have differing amounts of amniotic fluid from one day to the next, even from one hour to the next.
A score called an Amniotic Fluid Index (AFI) can be used to determine fetal well-being. It is done by adding the depths of four pockets of amniotic fluid around the baby. It is part of the more complete biophysical profile to assess whether a baby’s in danger or not. A normal AFI is about 12. But eight to 18 is normal, too. If there’s ample amount of fluid, then we can only assume that the baby’s kidneys are functioning normally, and then indirectly assume the kidneys are being perfused normally, driven by a normal fetal blood pressure, and normal heart activityï¿½in other words, everything’s working fine.
Therefore, a low AFI at or near term is an indication for delivery, either by induction or C-section. If there were to be a normal amount of fluid with rupture of membranes during an induction, then the low AFI was either temporary or wrong. But ultrasound’s the best thing we have to go by, even with its inherent error.
Other components of the BioProfile are:
- AFI, as described above
- Fetal Movement
- Fetal Tone
- Fetal Breathing Movements, another sensitive indicator of fetal well-being.
- Fetal Activity Determination (FAD), also referred to as a non-stress test (NST), in which accelerations of fetal heart rate are compared in real-time to fetal movement.
Each parameter can have a score of zero, one, or two. A perfect score would be 10 out of 10. A score of six or above can probably be closely observed. A score of five or less probably would indicate delivery. Eight or greater is probably a stable pregnancy.