Progesterone helps form and thicken the endometrial lining in the uterus of pregnant women. Without progesterone, a fertilized egg will not attach to the uterine wall and placenta will not support an embryo. Women who experience multiple miscarriages may have low levels of progesterone.

When it comes to the relationship between weight and health, there's no one-size-fits-all ideal you can call on to make sure you're on the right track. If your BMI is 18.5, you're on the low end of what's considered healthy, but you may or may not be at a healthy weight. If you're naturally very slim, a BMI of 18.

You may want to look like the supermodel on the cover of your favorite fashion magazine, but you might not be built quite the same way. Measuring your wrist to determine your body frame size can help you develop ideal expectations of a healthy weight specific for your height and build.

Carrying too much body fat increases your risk of disease, particularly heart disease and type-2 diabetes. Body fat scales, caliper tests and medical scans tell you the percentage of fat you have on your body.

Your body fat percentage indicates how much of your body weight is fat. Body fat percentage helps you determine your overall fitness level, regardless of your size or body type. For men, the ideal percentage of body fat depends on their activity level and age.

The Air Climber is a piece of home exercise equipment designed to burn body fat and increase lean muscle mass. The construction of the Air Climber simulates stepping in place and comes with a body cord for simultaneous upper body training.

Americans are not the only ones seeing their weight creep up on the scale -- obesity rates continue to rise across Europe as well. Europeans are now second only to Americans in the number of people who are overweight or obese.

The mesomorph body type is characterized by a naturally athletic physique with well-developed muscles. If you have this body type, you likely are able to put on muscle easily when you lift weights and find it fairly easy to gain and lose body weight.

Obese persons may benefit by starting a simple walking program to shed pounds and increase overall fitness. A walking routine burns calories and increases stamina, energy level and bone strength. Regular walking can reduce your risk of developing breast cancer or diabetes, according to the American Council on Exercise.

Body fat measurements give you a better understanding of the health of your body compared to the scale. Instead of only knowing your gross weight -- which includes bones, fluid, organs and connective tissue -- your body composition measurement tells you how much of that weight is made up of fat.

If you're concerned about your body fat levels, you have a few options that could help you figure out where on the scale from "healthy" to "obese" you are. Body mass index, or BMI, gives you a very rough estimate of whether you're at a healthy weight or not.

Metabolism refers to the collective chemical processes that convert food into energy. Similar to gas for your car, food is your body's fuel. If you have a fast metabolism, your body lacks fuel efficiency.