Amniotic fluid index variations after amniocentesis, amnioinfusion and amnioreduction: preliminary data.

We studied the relationship between the ultrasonographically measurable variations in the amniotic fluid index (AFI) and actual changes in the amniotic fluid volume induced by three differing invasive procedures: genetic amniocentesis, amnioinfusion and amnioreduction. We examined 50 patients, all between the 15th and 34th weeks of pregnancy, subdivided into three groups. The first group consisted of 33 women who underwent genetic amniocentesis, the second was of 11 patients submitted to amnioinfusion for oligohydramnios (AFI < 5 cm), and the third was composed of 6 patients affected by hydramnios (AFI > 20 cm) and treated with amnioreduction. In all cases AFI was measured before and after the invasive procedures and their variations (delta AFI) were correlated to the actual quantities of liquid infused or extracted. All the procedures gave rise to statistically significant AFI changes. After genetic amniocentesis, the mean change was from 12.0 to 10.9 cm (p < 0.005), after amnioinfusion from 3.1 to 10.6 cm (p < 0.0001) and after amnioreduction from 33.1 to 22.0 cm. (p < 0.005). However, a significant linear correlation between delta AFI and the fluid volume variations actually induced was found for amnioinfusion (y = 0.236537 + 0.031465x; R2 = 44.4%; p < 0.05) and for amnioreduction (y = -0.0584294 + 0.012008x; R2 = 89.8%. p < 0.00001). Only for amnioreduction is it possible, as proved by a multiple regression analysis, to improve the predictability of delta AFI, taking into consideration together with the quantity of fluid aspirated, the value of the preprocedure AFI (R2 = 92%; p < 0.05).