During week 18 of your pregnancy your baby’s bones begin to harden, a process called ossification. Bones in your baby’s legs and inner ear are among the first to ossify. With the bones in the inner ear now developed enough to function and the nerve endings from your baby’s brain now hooked up to the ears, your baby can hear sounds. He or she may hear your heart beating, your stomach rumbling or blood moving through the umbilical cord. Your baby may even become startled by loud noises.
Your little one can also now swallow. Inside your uterus, your baby may be swallowing a good dose of amniotic fluid every day. Scientists think this may help keep your amniotic fluid at the appropriate, constant level.
You should be able to feel the movements quite clearly when you are 18 weeks pregnant. Your nose may become blocked as pregnancy causes the membranes inside the nasal passages to swell. You may also notice an increase in vaginal discharge. You will find that there are several physical changes besides the predictable weight gain.
The skin is still wrinkled because the baby hasn't started to gain body fat and is very active. It is becoming aware of sounds outside the uterus and you may be able to feel it jumping at unexpected noises. The baby is now, when you are 18 weeks pregnant, around 5.6 inches (14 cm) long and weighs about 6.75 ounces (195 grams)