If you are just interested in checking the gender, you can go as early as 18 weeks. Any earlier, and the results may not be accurate, leading to an extra coat of paint for your bedroom.
To get good pictures, 3D ultrasounds are best performed between 24 and 34 weeks, and the best pictures are between 27 and 32 weeks.
If you would like to get a closeup shot of the face, then 27 to 28 weeks is the best time.
After 32 weeks, there is less fluid around the baby to work with, which can lead to suboptimal results. Also, after 32 weeks, the baby may have already descended into the pelvis, making getting any view of the baby impossible.
This means eight 8-ounce glasses a day. This helps clear up the amniotic fluid and ensures that there is enough fluid around the baby. Start well in advance; it doesn't do much good to only drink water the night before or the morning of your 3D ultrasound.
You may want to drink a glass of orange juice or a soda on the way to your appointment. The sugar and caffiene will help the baby wiggle out of its comfy spot.
You do not need to have a full bladder, as you would with your medical ultrasound. This is your time, and you want to be comfortable and relaxed so you can enjoy watching your baby. Having a full bladder does not help much with 3D ultrasounds. That being said, if your baby is in a particular awkward location and you already have had a failed attempt in getting good images of the baby, your ultrasound technician may request you come in the next time with a full bladder, though this should be a rare occurrence.
After 19 weeks, your baby is already developing a sleep pattern, and you may be able to predict the time that your baby is most likely to be awake.
If your baby is asleep at the time of your ultrasound appointment and you want to make your baby move, try drinking some orange juice. This has been shown to help stimulate the baby to move. For some women, chocolate also works. Otherwise, try walking around.
The Position of the Baby
Excessive Fat Tissue or Skin
Murky Amniotic Fluid