amniotic sac

noun

plural amniotic sacs

: a pair of thin membranes forming a fluid-filled closed sac around the embryos or fetuses of reptiles, birds, and mammals

When the amniotic sac is completed it becomes filled with a watery fluid in which the embryo is suspended.

—Bradley M. Patten

Usually, the amniotic sac ruptures when a mother's water breaks before labor ensues.

—Conor Skelding

see amnion sense 1, chorion sense 1

Examples of amniotic sac in a Sentence

Recent Examples on the Web

At her first sonogram while pregnant with her son, Sallie Bennett said technicians thought there was a problem with her amniotic sac, but later pivoted to an issue with the fetus’ left hand. — Edward Lee, Baltimore Sun, 20 July 2026

The My Mini Baby Mom & Surprise Doll by the toy company Zuru features a pregnant doll with a removable stomach that contains a very realistic amniotic sac with a tiny plastic baby and slime inside. — Georgia Slater, PEOPLE, 17 July 2026

Early May 26, 2024, McElroy felt her amniotic sac break in the bathroom. — Abigail Brooks, NBC news, 13 May 2026

The scans found that her uterus was empty, but a nearly full-term fetus in an amniotic sac was hiding in a small space in her abdomen, near her liver. — Laura Ungar The Associated Press, Arkansas Online, 28 Dec. 2025

Word History

First Known Use

1831, in the meaning defined above

Rhymes for amniotic sac

• ammoniac
• biofeedback
• counterattack
• demoniac
• elegiac
• noncardiac
• paranoiac
• aback
• attack
• backpack
• backtrack
• bareback

Medical Definition

amniotic sac

noun

: amnion