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The Purpose of Amniotic Fluid and Amniotic Sac


What is amniotic fluid and what is it’s purpose? Also referred to as the “bag of waters”, the most pregnant women generally know about it is that about the time labor begins their amniotic sac will break, or be broken by their midwife or doctor, causing the start of the delivery process. They don’t however know what its purpose is during a pregnancy.

The amniotic fluid is the clear, slightly yellowish fluid within the amniotic sac that surrounds the baby in the uterus. The baby grows in this amniotic sac, surrounded by the amniotic fluid, as he learns to move his limbs, open his eyes and breathe. Amniotic fluid levels generally sit at approximately 800ml through most of the pregnancy, dropping slightly in most cases to about 600ml by the time a woman reaches the 40 week mark.

The amniotic fluid has many purposes. It helps to cushion hard blows and jolts to your belly to protect the baby and it allows your baby the freedom to move while permitting symmetrical musculoskeletal development. It also maintains an even temperature so that your baby does not get too hot or too cold, even if you are extremely hot or cold.

Amniotic fluid also helps your baby develop his lungs. While in the womb your baby practices breathing by breathing in and out the water in the amniotic sac. The baby swallows and inhales the amniotic fluid and replaces the volume in the amniotic sac by urinating and exhaling the liquid.

In some cases, a woman may have too much or too little amniotic fluid. Having too much is called polyhydramnios and having too little is called oligohydramnios. In either case, a woman might be watched more closely by her physician throughout her pregnancy.

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18 Responses to “The Purpose of Amniotic Fluid and Amniotic Sac”

  1. 18
    Michelle Says:

    Heya I shud be ten weeks 5 days preg but I went and got an internal scan because of cramping and shows de sac does measure 10 weeks but the baby only measure 3.5mm which is dat of an embryo I’ve to go back Friday I’ve no bleeding or anything has anyone else go e thru dis and has ur baby survived dis is my first pregnancy was so excited plz help

  2. 17
    a martin Says:

    I went to the doctor today and he did a ultrasound and it showed the sac but no fetus. I had some blood work done to check how far along i am but they estimate 2 maonths i’m scared and nervous does anyone have a coment

  3. 16
    amanda payne Says:

    i read a question at the bottom below the article on a woman the
    “vomitted” amniotic fluid. that is impossible. you cannot vomit the amniotic fluid because it is in your uterus, not stomach she must have vomitted bile.

  4. 15
    Kristin Says:


    It sounds like a placental abruption. I had one at 21 weeks 4 days. I had fist size clots coming out once a week since six weeks pregnant. Then when I was 20 weeks I had 2 or 3 clots a week until I lost her. Let the doctor know that you need to see a specialist and be on bedrest. If you feel stabbing pains in your stomache go to the emergency room immediately! I had stabbing pain and they sent me home because it didn’t show on the contraction monitor. Two days later I was back with the same pain and delivered my baby. She live for 35 minutes.

  5. 14
    D.Figley. Says:

    I am 22 weeks along with my first baby, and she seems to kick me in the cervix and bladder alot, but when she hits my cervix it feels like i should expect a gush of fluid, but nothing happens. Is it possible for her to break the bag of waters or cause dialation of the cervix from kicking it? Im extremely paranoid of something going wrong because of my mothers obstetrical history, she had a miscarriage, then had me at 32 weeks due to preterm labor, hyperthyroidism, and the umbilical cord wrapped around my neck tightly, she then had another miscarriage, followed by my brother 2 weeks late, i am unaware of any problems, then 8 years later had my sister, with bleeding and preterm labor, and 2 years later had my littlest brother, with preterm labor, bleeding, in the hospital every week for IVs. They told her after me she would never be able to carry a baby to term. Should i be concerned if nothing has gone wrong yet?

  6. 13
    ghel Says:

    Hi got two ultra sound when I was in my 4 weeks and no baby found they said too early early and need follw up after 2 weeks. The size of sac is 1.08. After 2 weeks I undergone onother ultra sound sac measures 3.4 meters and no fetus found. Is this possible that sac is still growing even w/o fetus? Is this a sign of missed miscarried?

  7. 12
    kimberly Says:

    Hi, There Im pregnant with twins Im about 16weeks along and I have a question or I need advise can some one help on monday 06-14-10 I started spoting. I had a doctors aptment that thay he said every thing looked ok. well on tuesday 06-15-10 I started bleeding alot i called my docter and went again some thing had came out and it was big, round and kind of flat he said it could have been a blood clot. he did a altersound and he said im about 16 weeks and the is way too much fluid and my uteres is biger then it should be… and there is not much they can do. Is there any thing any one can do? what can be the reason of all that? I dont know I need info or ??? see in 2004 I had a miscarrage at about 4months. and in 2006 i had a premater baby at 22weeks he pased away after 3hours and in 2008 my son was burn 4-28-08 little problems every thing went good he was born a day before his due date.

  8. 11
    Stages of Labor & Delivery | I Love Natural Childbirth Says:

    [...] stage of labor where they are more comfortable and surrounded by familiar things. As long as their water has not broken, they may choose to take baths or showers, light candles, play music, or just sit [...]

  9. 10
    Grace Says:

    I am 40 weeks pregnant and my water broke 2 times in gushes yesterday at 18h00 and 23h15, I was up all night with contractions with intervals of 5 mins in between. I don’t want to go spend my time at the hospital but I still have no urge to push, would anyone know if this is normal and what should I do?

  10. 9
    Breech Baby | Pregnancy | Baby, Pregnancy, and Parenting at Babies Online Says:

    [...] time for the babies to flip around. It can also happen if there is a smaller than normal amount of amniotic fluid, a short umbilical cord, or other uterine abnormalities. If your baby has a congenital defect he is [...]

  11. 8
    Phases and Stages of Labor | Pregnancy | Baby, Pregnancy, and Parenting at Babies Online Says:

    [...] stage of labor where they are more comfortable and surrounded by familiar things. As long as their water has not broken, they may choose to take baths or showers, light candles, play music, or just sit [...]

  12. 7
    Premature Labor | Pregnancy | Baby, Pregnancy, and Parenting at Babies Online Says:

    [...] Leaking of fluid [...]

  13. 6
    Meconium | Labor & Birth | Baby, Pregnancy, and Parenting at Babies Online Says:

    [...] are born. Meconium is the first bowel movements from a newborn that includes cells, mucus, bile, amniotic fluid and lanugo that is stored in the baby’s intestines while in utero. It is dark green, almost [...]

  14. 5
    sherry Says:

    My son was born still in his amniotic sack. He was just fine!The doctor said “it is good luck” he called it A GOLDEN BIRTH. My labor was the same as my other children. So I guess it does’nt matter either way. Good Luck

  15. 4
    patricia Says:

    What happens when a baby is born with in the amniotic sack? I mean the baby comes out of the mother while he /she is still in the sack?

  16. 3
    Diana Says:

    Nadine – It is impossible for the mother to vomit amniotic fluid. The amniotic fluid is only in the uterus, which is not connected to your digestive track in any way. What you vomited was probably just bile, which can cause minor damage to your esophagus and teeth due to the stomach acid. Repeated exposure to stomach acid (repeat throwing up) can cause progressivly higher amounts of damage to the esophagus and teeth. I would question any nurse who told you that you threw up amniotic fluid since she clearly does not understand basic biology.

    Monique – Hopefully your friend’s second child is still doing fine. While an amniotic sac can spring a leak or get a small rupture it can sometimes (key word being sometimes) repair itself as long as it’s small enough. There are pioneering attempts to manually seal ruptures that occur that do not seal naturally by using biological glue. If you google ‘amniotic sac repair’ at least one story will show up.

  17. 2
    monique arroyo Says:

    i have a friend who is 15weeks pregnant. She is pregnant with twins when she was 13weeks into the pregnancy her amniotic sac broke in twin number 2 so far twin 2 is still hanging on. She is so scared and her doctors aren’t really telling her anything. Please Help!!!!

  18. 1
    Nadine McDonald Says:

    Hi there, I need help with this question. when i started labour with my first son, i vomited up the amniotic fluid, the nurse at the time told me that its going to damage my teeth, can you tell me if that is true? I really need your help in answering this. Thank you. Please send it to my email address above.

    Nadine McDonald.

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