What is Amniotic sac?
[[File:Human fetus 10 weeks with amniotic sac - therapeutic abortion.jpg|thumb|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. ==Development== The amniotic sac starts to form and fill with amniotic fluid just days after a woman gets pregnant.<ref name=nhssac>{{cite web |url=http://www.nhs.uk/chq/Pages/2310.aspx?CategoryID=54 |title=What is the amniotic sac? |author=<!--Staff writer(s); no by-line.--> |date=December 21, 2015 |website=NHSChoices |publisher=National Health System of the United Kingdom |access-date=February 12, 2016 }}{{Dead link|date=January 2025 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> At first, the amniotic fluid is made from the mother's [[blood plasma|plasma]] (the liquid part of her [[blood]]).<ref name=nature>{{cite journal |author=Underwood MA; Gilbert WM; ''et al.'' 2005 |title=Amniotic Fluid: Not Just Fetal Urine Anymore |url=http://www.nature.com/jp/journal/v25/n5/full/7211290a.html |journal=Journal of Perinatology |year=2005 |volume=25 |issue=5 |pages=341–348|doi=10.1038/sj.jp.7211290 |pmid=15861199 |s2cid=1302607 |access-date=February 13, 2016}}</ref> At first, the amniotic fluid is made mostly of water with [[electrolyte]]s (salts). However, by the 12th to the 14th week of pregnancy, [[protein]]s, [[carbohydrate]]s, [[lipid]]s, [[phospholipid]]s, and [[urea]] are all in the amniotic fluid.<ref name=nature/> 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.<ref name=LARSEN2001>{{cite book|last1=Larsen|first1=William J.|title=Human embryology|url=https://archive.org/details/humanembryology0000lars|date=2001|publisher=Churchill Livingstone|location=Philadelphia|isbn=0443065837|page=[https://archive.org/details/humanembryol