Playing With Your Fetus: Noise Games
By the time your fetus is 18-20 weeks old, her hearing is intact. If you talk to her, she will hear you, and she will also hear what is going on around you (muffles by your belly as it may be). Of course Mom's voice will be the loudest and clearest, but Baby can also hear Dad, siblings, and other relatives when they talk to her. The voices Baby hears most in the womb will tend to be those she responds to turns to for comfort when born. Now is the time you can start using audio in womb games with baby!
Try talking to Baby will provide him with audio stimulation and an early introduction to different family member's voices. You can even buy books geared toward Baby while he is still in your belly. Older siblings may enjoy reading the their new little brother or sister to be, or sharing story time with his while you read to both. Hearing your voice is soothing and fun for Baby.
Music is another great idea. There is no need to buy a fancy listening device, simply being in the room with music will let your baby listen. Classical has been touted to aid in brain development, but exposing Baby to different types of music and sounds is good too. Listen to your favorite music and it may be Baby's too! Whatever makes you want to get up and dance will release endorphins into your and Baby's bloodstream to give you both a feeling of well-being.
You may also want to try just exposing Baby to different noises in general: paper crinkling, balls bouncing, tub drains draining, etc. See if Baby reacts to certain noises she may find new or exciting. Chances are she will!