Your baby's eyelids and eyebrows are well developed by this week of pregnancy, but the eyelids remain fused. The cells that are destined to become your baby's fingernails were present at 10 weeks, and the cells for the toenails were present four weeks later.

Now, at 23 weeks, the nails are just beginning to make an appearance at the base of the nail bed. The nails will grow continuously throughout life, but it will be several weeks before they have reached the tips of the fingers and then the toes.

Your baby's skin is developing quickly and often appears wrinkled at this stage; it is as if the baby has yet to grow into it. Your baby is now covered in extremely fine and short hairs, known as "lanugo." This layer of hair will be almost completely lost before birth. The hairs help trap vernix onto the surface of the skin; this is the white, greasy layer that you often see in patches on a baby's skin at birth. It collects in the skin folds and creases and helps protect the baby's skin not only from the water content of the amniotic fluid, but also the waste products within it.

As your pregnancy advances, your baby's kidney function is improving and the amniotic fluid produced becomes increasingly similar to urine in its composition.

Your posture will naturally change as a result of pregnancy; this is due to the extra weight you're carrying and the softening of your joints.

Prior to pregnancy, your center of gravity was directly over your hips; during later pregnancy it shifts forward to your enlarged abdomen. This dramatic shift in your center of gravity increases the curve of your lower spine, and can result in lower back pain (see Banish backaches). The weight you gain during pregnancy can also put strain on the back.

Exercises can help balance your body and alleviate the muscular aches associated with changes in your posture. It's important to adapt to these postural changes in pregnancy:

• Do abdominal exercises , to strengthen the core muscles, as well as back stretches. These help maintain good posture and avoid back pain later in pregnancy.
• Be aware of the way you're walking and standing: pull your shoulders down and back, do not arch your lower back and keep your pelvis in a neutral position.
• Avoid balancing anything on your hip, because this can affect your hip and back alignment.
• Don't hold a phone between your head and shoulder because this can result in neck pain.