Some people claim they can predict the baby's sex by the way you're carrying, but, again, there is no scientific proof that this is true. The position of the baby during the ultrasound is key, and if your baby's curled up or facing the wrong way, you may have to wait until your next appointment. The amniocentesis identifies more genetic diseases than the CVS and also reveals the gender of the baby. Still others use a "pendulum test" in which an object is suspended over the pregnant belly and the baby's sex is revealed depending on which way the pendulum swings. This test isn't without risk, however, and isn't performed simply to determine the sex of your baby. Don't get frustrated if the doctor can't tell what the baby's sex is on ultrasound. Kathryn Rateliff Barr has taught birth, parenting, vaccinations and alternative medicine classes since Saad Ramzi Ismail, recommends that parents ask the sonographer to identify the location of the placenta. However, this test is infrequently used. Again, there is no documented proof that this test works. Studies include midwifery, naturopathy and other alternative therapies. The test is performed for the same reasons your doctor might recommend the CVS or if you have an abnormal ultrasound. For obvious reasons, it's usually easier to see if your baby is a boy. I'm often asked if you can tell the baby's sex by the heart rate—based on the myth that one sex is faster than another—but that's just an old wives' tale. Another test that can look at the baby's chromosomes is called CVS chorionic villus sampling , which is performed during the first trimester to look for problems with the baby's chromosomes. Sampling Amniotic Fluid An amniocentesis samples amniotic fluid using a needle inserted into the uterus through the abdominal wall, generally performed in the 16th week of pregnancy or later. The test, usually given to moms 35 or older, involves inserting a needle into the uterus to remove a small amount of amniotic fluid.