The terms "blooming" or "glowing" are often used to describe pregnant women, especially during the second trimester. The ideal image is a woman with thick shiny hair and perfect skin that has a healthy blush.
The improved condition of your skin is thanks to the hormone estrogen (pregnancy hormones can have positive effects, too!) and the increased blood supply to the skin; the many blood vessels just below the skin's surface give you a healthy glow, or at least stop you from looking pale and tired. The glands also secrete more oil, giving your skin a healthy-looking sheen.
Again due to hormonal changes, your hair may look thicker. Less hair than normal falls out during pregnancy and hair grows more quickly. After the birth you may find that your hair appears to be falling out more than normal as you lose the hair that's built up during the nine months. Normal hair loss is about 100-125 hairs a day; after the birth you might lose 500 hairs a day.
If you don't feel you match this picture of good health, it may just be that you can't see it yourself, especially if you're still adapting to your pregnancy. If you're looking pale and feeling tired, speak to your doctor because you may be anemic and need to boost your iron intake (see Iron-rich foods).