# amniotic fluid volumes

Amniotic fluid volume (AFV) is a function both of the amount of water transferred to the gestation across the placental membrane, and the flux of water across the amnion.

#### Physiology

##### Change in volume through gestation

The AFV undergoes characteristic changes with gestation. It progressively rises.

- 10 weeks gestation: ~10-20 mL
- 16 weeks gestation: ~250 mL
- 33 weeks gestation: ~800 mL
- 38-39 weeks: plateaus at ~1000 mL
- finally decreases at 40 weeks to ~800 mL

##### Rate of change

At 8 weeks the volume increases by ~10 mL/week, at 13 weeks the AFV increases by 25 mL/week and reaches a maximum rate of 60 mL/week at 21 weeks gestation. The weekly volume increment then decreases and reaches zero at about 33 weeks of gestation at which point the mean AFV reaches its peak. After this point, the amniotic fluid volume declines at a rate of ~8% per week. During the first half of pregnancy, the amniotic fluid volume is closely correlated with fetal weight. The ratio of amniotic fluid to fetal volume increases until about 30 weeks of gestation and then appears to decline.

#### Radiographic features

##### Ultrasound

Ultrasound is the modality of choice of assessing amniotic fluid volumes. The AFV can be assessed by ultrasound by using three main indirect parameters:

#### See also

##### Siehe auch:

- amniotic fluid index
- Polyhydramnion
- Oligohydramnion
- amniotic fluid discordance
- two diameter pocket method
- single deepest (maximum vertical) pocket method