what is mucus plug?

Question

and why does it happend

Answer 1

During pregnancy the cervix (top of the vagina) is sealed with a mucus plug, to protect the growing infant from infection. When in labor, the cervix expands and the mucus plug comes free. It looks like a lot of thick, jelly-like substance, sometimes with little streaks of blood in. This means that the baby should soon be on the way.

** The mucus produced at ovulation serves the opposite purpose, it doesn't seal. It is designed to make it easier for the sperm to travel to meet the egg, thus assisting fertilization.

Answer 2

In a woman, a mucus plug is formed in her cervix after menstruation. It lightens up as ovulation approaches. It is also created when a woman becomes pregnant. The creation of the plug is directed by one of the female hormones (estrogen or progesterin). The point of it is to prevent infection of the uterus or other foreign substances from entering the uterus. Hormonal birth control simulate pregnancy by preventing ovulation and creating this plug.

edit: yes, the mucus produced at ovulation is indeed lighter, because it lightens up as ovulation approaches. Right after menstruation, however, a mucus plug is formed to prevent infection (not just during pregnancy).