Amniotic Fluid
Amniotic fluid is the warm, fluid cushion that protects and supports your baby as they grow in the womb. This important fluid contains, hormones, immune system cells, nutrients, and your baby’s urine.
At its highest level, the amniotic fluid in your belly is around 1 quart. After 36 weeks of pregnancy, your fluid levels start to decrease as your body prepares for your baby’s delivery. When your doctor performs ultrasound prior to delivery, they’ll estimate the amount of amniotic fluid your baby is surrounded by.
Your doctor can measure your amniotic fluid levels using an ultrasound. There are two calculations on ways to measure, known as the amniotic fluid index (AFI) or the maximum vertical pocket (MPV). Doctors consider your fluid levels to be low if your AFI is less than 5 centimeters (cm) or your MPV is less than 2 cm.
Source: https://www.healthline.com/health/pregnancy/leaking-amniotic-fluid#fluid-levels