From Robin Elise Weiss, LCCE,
Your Guide to Pregnancy & Childbirth.
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Of all of the modern miracles of science, we still don't know where amniotic fluid really originates.

We know that the fluid after a certain point does contain fetal urine, but how can we explain it prior to the baby's ability to make urine?

Other amazing facts include that the amniotic fluid continually replaces itself at the rate of every three hours.

That said, we've been trying to define what is normal amniotic fluid and what is abnormal.

There are four categories of amniotic fluid:

1. Oligohydramnios
2. Pockets seen greater than 1 cm in diameter (normal)
3. Adequate fluid, seen everywhere between the fetus and uterine wall (normal)
4. Polyhydramnios

This measurement is commonly taken by using an ultrasound to determine the Amniotic Fluid Index (AFI). The most recent studies say that the AFI is not a great predictor of the Amniotic fluid volume (actual amount of fluid). In fact, another study confirmed these finding, for either extreme in fluid volume.