The density of a substance refers to how close together the molecules in that substance are packed. compare the density of water in its three phases.

High density in solid phase, medium density in liquid phase, and low density in gas phase

the level of progesterone is low at the pre-ovulatory phase of the cycle but it gradually increases and the levels are high at the luteal phase. if pregnancy occurs, the level of progesterone will be high throughout the pregnancy.

if egg is fertilized and the mother gets pregnant, progesterone starts preparing the uterus for the implantation. it starts building up the lining of uterus and make it hostile of the period of pregnancy.