What does the hormone progesterone do during the menstrual cycle?

Does it maintain the thickness of the uterus lining?
I'm not sure.
But i do know oestrogen helps the development of the lining, though.

EDIT: Are levels of oestrgen high or low during ovulation?

At the start of the menstrual cycle, oestrogen levels rise. This rise in oestrogen causes the endometrium (uterus lining) to thicken because it starts to receive a richer supply of blood.
About two weeks into the cycle, LH (Luteinizing Hormone) levels rise dramatically; this surge in LH triggers ovulation and also causes the follicle to become a corpus luteum.
This corpus luteum then starts to produce and release progesterone (it also releases small amounts of oestrogen).
Progesterone carries on maintaining the endometrial lining for a potential pregnancy; it also stops a new follicle developing and prevents the uterus from contracting.
However, if the egg does not fertilize then progesterone levels start to fall; the corpus luteum degenerates, the lining starts to break down/shed and the uterus can now contract which leads onto menstrual bleeding.

During ovulation, oestrogen levels are relatively low, but not absent. As stated above, the corpus luteum does release oestrogen as well, but only small amounts. It secretes larger amounts of progesterone than it does oestrogen, which is why progesterone levels are much higher during ovulation.

In short; progesterone is released from the corpus luteum during ovulation. Progesterone carries on maintaining the uterus lining, it stops a new follicle developing and prevents the uterus contracting. With no fertilization, progesterone levels fall causing the shedding of the uterus lining and menstrual bleeding.

Hope that helped! :]

Progesterone helps prepare the lining of the uterus (endometrium) to receive the egg if it becomes fertilized by a sperm. If the egg is not fertilized, progesterone levels drop and menstrual bleeding begins.

During the reproductive years, the pituitary gland in the brain generates hormones (follicle-stimulating hormone [FSH] and luteinizing hormone [LH]) that cause a new egg to mature and be released from its ovarian follicle each month. As the follicle develops, it produces the sex hormones estrogen and progesterone, which thicken the lining of the uterus. Progesterone levels rise in the second half of the menstrual cycle, and following the release of the egg (ovulation), the ovarian tissue that replaces the follicle (the corpus luteum) continues to produce estrogen and progesterone.

Estrogen is the hormone that stimulates growth of the uterine lining (endometrium), causing it to thicken during the pre-ovulatory phase of the cycle

see in Google. type progesterone and u will get ur answer. i studied a lesson on this in my biology class two years back but now i forgot. i am sorry.