Amniotic fluid has been described as a romper room for a developing baby because it gives your baby a protected space to move around in. It does that and a lot more. The amniotic sac is where your baby lives and grows inside your womb. Your baby drinks it, breathes it, and pees it out.
It starts to fill with fluid within days after you become pregnant. The first fluid comes from you. As your baby grows, your baby will swallow the fluid and replace it with urine. By 20 weeks of pregnancy, all the amniotic fluid is recycled urine.
Amniotic fluid is odorless and clear. It may have a slightly yellow tint. It reaches a peak volume of about one quart by 36 weeks of pregnancy and then starts to decrease as your baby gets ready to come into the world. Here are 7 things amniotic fluid is doing for your baby inside your womb:
- As you move around, your amniotic fluid cushions your baby’s ride. It is your baby’s shock absorber.
- Giving space. Giving your baby space to tumble and kick is really important. This movement allows your baby’s bones and muscles to develop. It also keeps your baby’s lifeline – the umbilical cord – from getting compressed or crimped.
- Maintaining a safe temperature. The outside world can be too cold or too hot, but your amniotic fluid is a very good thermostat. It keeps womb temperature just right.
- Developing the lungs. Your baby starts to breath in amniotic fluids as his or her lungs develop. This breathing strengthens the muscles of the lungs so that when it is time to start breathing oxygen, the lungs are good to go.
- Developing the digestive system. As your baby’s digestive system develops, your baby swallows amniotic fluid. This gets you baby’s digestive tract conditioned to receive milk after birth.
- Protecting against infection. Antibodies that you have against certain infections may be found in your amniotic fluid. These antibodies may help your baby fight off infections in the first weeks of life. An example is antibodies to a virus that frequently causes lung infections in children (respiratory syncytial virus). Your baby may be protected from this virus by breathing in antibodies in your amniotic fluid. 
- Providing nutrients. The same important nutrients you have in your blood also make their way into your amniotic fluid. Since your baby is constantly swallowing amniotic fluid, they can be a source of nutrition. Nutrients found in amniotic fluid include B vitamins and important mineral like zinc, iron, and copper.
Too much or too little amniotic fluid can be a problem, but these conditions are rare. Not enough fluid – called oligohydramnios – occurs in about 4 percent of pregnancies. There are several causes, but the most common cause is a pregnancy that goes past its due date. Treatment could include induction of labor or replacement of fluid, which is called amnioinfusion.
Too much amniotic fluid – polyhydramnios – occurs in only 1 percent of pregnancies. Again, there are many possible causes. Treatment could include removal of fluid, called amniocentesis or a medication called indomethacin.
In most cases, your amniotic fluid will do all its important functions without any problems. Its last role will be to tell you that labor is coming soon. When the amniotic sac opens, the fluid that comes out is your water breaking. For most women that signals end of the first stage of labor.