When first formed, the amnion is in contact with the body of the embryo, but about the fourth or fifth week amniotic fluid (also called "liquor amnii") begins to accumulate within it. This fluid increases in quantity and causes the amnion to expand and ultimately to adhere to the inner surface of the chorion, so that the extra-embryonic part of the coelom is obliterated. The amniotic fluid increases in quantity up to the sixth or seventh month of pregnancy, after which it diminishes somewhat; at the end of pregnancy it amounts to about 1 liter.