• placenta
  • Depending on the position of the baby, placenta, amount of fluid, or mother's anatomy, sometimes the amniocentesis cannot be performed. (nyhq.org)
  • fluid
  • Amniocentesis is usually performed between the 12th and the 16th week, after the last menstrual period when there is enough fluid surrounding the baby that a sample is possible. (askdrsears.com)
  • Citation
  • citation needed] Testing for HDN involves blood work from both mother and father, and may also include assessment with amniocentesis and Middle Cerebral Artery scans. (wikipedia.org)