The foetus develops in a fluid-filled space that is encased by an amniotic sac
- The amniotic sac separates the foetus from the mother and hence functions as a barrier against infection
The amniotic sac is filled with a protective liquid called amniotic fluid, which serves a number of key roles:
- The fluid is largely incompressible and good at absorbing pressure, and so protects the foetus from impacts to the uterus
- The fluid also creates buoyancy so that the foetus does not have to support its own weight while a skeletal system develops
- Finally, amniotic fluid prevents the dehydration of foetal tissues
The amniotic sac ruptures when a woman comes to term during labour – this is known as her ‘waters breaking'
Ultrasound of the Amniotic Sac