Objective — to study the proteomic profiling and posttranslational modifications of amniotic fluid proteins during physiological and placental insufficiency-complicated pregnancy. Subject and methods. Examinations were made in 42 pregnant women, of whom 20 had pregnancy complicated by compensated placental insufficiency and 22 had uncomplicated pregnancy. Protein profiles were studied using high-resolution two-dimensional electrophoresis and time-of-flight mass spectrometry. Amide and amine protein functional groups were determined spectrophotometrically, by measuring the color intensity of the end-products of biochemical reactions in the visible region of the spectrum. Placental tissue was histologically examined to verify placental insufficiency. Results. Eight proteins were not found in second-trimester placental insufficiency in the amniotic fluid as compared with the protein spectrum during physiological pregnancy, the number of missing proteins in third-trimester placental insufficiency increased to 11. Among these, there were proteins controlling the growth and development of the fetus, its adaptation to intrauterine existence, proteins regulating a balance between pro- and antioxidative processes, which were involved in the mechanisms of biological oxidation and cell energy provision; 3 proteins undetected in second- and third-trimester physiological pregnancy were, on the contrary, found in placental insufficiency; one more protein increasing apoptosis, the secretion of embryotoxic cytokines were identified only in the second trimester. Posttranslational modifications of amniotic fluid proteins were also found in placental insufficiency. There was a decline in the number of amine and amide groups and an increase in the ratio of readily and hardly hydrolyzable groups. Conclusion. The revealed changes in the composition and properties of amniotic fluid proteins can be primary components in the chain of molecular damages in the fetoplacental complex in placental insufficiency.