The potential risks of midtrimester amniocentesis resulting from the loss of amniotic fluid are reviewed. Amniotic fluid fulfils important functions in fetal well-being, but its replacement time after amniocentesis is not known. A review of experimental amniocentesis in animals suggests risks to limbs and structural changes in fetal lungs. In humans, orthopaedic abnormalities and respiratory difficulties appear to be a risk of amniocentesis, and studies addressing these risks are also reviewed. Continued investigation of risks from fluid loss at midtrimester amniocentesis is recommended.