There are multiple prenatal screening and diagnostic test that a pregnant mother can avail herself of to make sure that her baby is chromosomally typical. Screening tests are generally done through the state and they can include an integrated screen which would be an ultrasound at approximately 12 weeks looking at the thickness of the baby's neck combined with the blood test that looks at certain hormones in a mother's body. These 2 tests can tell an initial screen for down syndrome, Trisomy 18. And, then, in the second trimester, the mother gets a second blood test. And, all three of these tests, the 2 blood tests and the nuchal translucency get combined to give the mother an overall screening test for down syndrome, Trisomy 18 and defects in the baby's spine. Some other newer screening test include looking for noncellular fetal DNA in the maternal circulation and this test can be up to 99% predictive in looking for down syndrome and some of the other chormosomal abnormalities. A diagnostic test would be done in cases where the screening test came out at a high positive risk or the mother wanted more definitive information that can be given by a screening test, and this will include the CVS which is done at approximately 12 to 14 weeks. A little bit of tissue is taken by a needle from between the baby and the placenta and the chromosomes are analyzed or an amniosynthesis where fluid is taken from around the baby in the amniotic sac, and again, the chromosomes are analyzed for appropriate number. Now, the amniosynthesis is not done until between 18 and 20 weeks. Often by this time, it is getting a little bit late to be making decisions about your pregnancy and while decisions can still be made, it maybe more uncomfortable to make decisions this late in the game. The CVS and the screening tests can be done earlier. In general, these days, amniosynthesis is reserved for when issues arise based on the second trimester ultrasound and chromosomes may want to be obtained to look in to those issues.