Amniotic sac

A ten-week-old fetus, surrounded by the amniotic sac, which is filled with amniotic fluid

The amniotic sac holds a fetus while it is developing during pregnancy. The amniotic sac is filled with amniotic fluid, which protects the fetus.


The amniotic sac starts to form and fill with amniotic fluid just days after a woman gets pregnant.[1] At first, the amniotic fluid is made from the mother's plasma (the liquid part of her blood).[2]

At first, the amniotic fluid is made mostly of water with electrolytes (salts). However, by the 12th to the 14th week of pregnancy, proteins, carbohydrates, lipids, phospholipids, and urea are all in the amniotic fluid.[2] These things help the fetus grow.

As the fetus gets bigger, more amniotic fluid gets created. By the time the baby is born, there is about one liter of amniotic fluid in the amniotic sac.[3]

Other Languages
العربية: كيس سلوي
Deutsch: Fruchtblase
Ελληνικά: Αμνιακός σάκος
English: Amniotic sac
español: Saco amniótico
français: Sac amniotique
italiano: Amnios
עברית: שק שפיר
português: Bolsa amniótica
svenska: Fosterhinna
中文: 羊膜囊