Will a test for downs syndrome also pick up if a child will have edwards syndrome?

Depends on test. The chromasome study preformed during chorionic villous sampling will pick up the edwards-patau syndrome trisomy 18, down syndrome t21, & the major chromasome defects to the level of the study. High resolution studies can pick additional problems. Some ob's use a blood test to decide if cvs would be needed in low risk population & screening tests are less accurate pro/con & may not pick up either.
Depends on test done. The blood test for Down's syndrome can also SUGGEST that a child may have Edwards Syndrome. The diagnosis is confirmed by carrying out chorionic villus sampling (CVS) or amniocentesis – invasive tests carried out during pregnancy to detect whether the unborn baby could develop, or has developed, an abnormality or serious health condition. Talk to your Ob/Gyn.