Moms-to-be have a lot of questions regarding their pregnancy and pending parenthood. How much weight gain is too much? What foods are safe to eat? What are my delivery options? But one of the most common queries readers send in to PregnancyToday.com isn't about healthy habits or delivery. A lot of moms want to know what the fluid is that fills their bodies and cushions their babies: amniotic fluid. What exactly is it, and what is its role in pregnancy?

"Amniotic fluid is one of the main ingredients that keeps a baby doing well," says Dr. Robert Atlas, the chairman of the department of obstetrics and gynecology at Mercy Medical Center in Baltimore, Md. "It's a combination of solutes – substances within our own bodies – which help bathe the baby. Early on, it consists of electrolytes, similar to what is in our own blood. The baby then begins to urinate, and that becomes one of the big components of the fluid in the cavity."

This means that the volume of amniotic fluid increases by 10 milliliters until 8 weeks, says Dr. Abu Alam, an OB/GYN affiliated with Overlook Hospital in Summit, N.J. "At this point, the fluid increases up to 60 milliliters per week until 21 weeks when it starts to gradually decline to a steady rate by 33 weeks of pregnancy," says Dr. Alam. "By the end of the pregnancy, it's down to a single liter."

And the purpose of these fluctuating levels of fluid? "Amniotic fluid serves to cushion the fetus to help the baby have normal development and supports the umbilical cord from compression between the fetus and the uterus," Dr. Alam says.

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