What is the miscarriage risk with amniocentesis?

RCOG guidance is specific: women should be informed that the additional risk of miscarriage following amniocentesis or CVS, performed by an appropriately trained operator, is likely to be below 0.5%. That is roughly 1 in 200 or lower — and it is considerably lower than the 1 in 100 figure still widely quoted, including in older patient information. If you have been given a higher number, it may be out of date. The word "additional" matters. This is the risk added by the procedure, over and above the background chance of miscarriage that exists in any pregnancy. Separating the two is genuinely difficult, which is part of why estimates have varied. The underlying data, from systematic reviews cited in the guideline: weighted pooled procedure-related loss of 0.11% for amniocentesis and 0.22% for CVS in one analysis, and 0.35% for both procedures in an updated analysis including over 64,000 amniocenteses and 19,000 CVS procedures. Notably, six of ten amniocentesis studies reported a risk of 0.2% or less, and three of six CVS studies found no additional risk at all. Two things genuinely affect your risk: Operator experience. ISUOG notes lower fetal loss rates where more than 100 procedures are performed per year. Ask how many your operator does. Number of needle insertions. Three or more attempts increases risk; if more than two are needed, delaying 24 hours has been suggested. For twins, the additional risk is around 1%. Ask your unit for their own audited rate as well — but the figure above is a sound starting point.