Robbins Basic Pathology, 9th Ed., Chapter 6, p. 247: "Disruptions result from secondary destruction of an organ or body region that was previously normal in development; thus, in contrast with malformations, disruptions arise from an extrinsic disturbance in morphogenesis. Amniotic bands, denoting rupture of amnion with resultant formation of "bands" that encircle, compress, or attach to parts of the developing fetus, constitute the classic example of a disruption. A variety of environmental agents may cause disruptions. Disruptions are not heritable, of course, and thus are not associated with risk of recurrence in subsequent pregnancies.
Deformations, like disruptions, also represent an extrinsic disturbance of development rather than an intrinsic error of morphogenesis. Deformations are common problems, affecting approximately 2% of newborn infants to various degrees. Fundamental to the pathogenesis of deformations is localized or generalized compression of the growing fetus by abnormal biomechanical forces, leading eventually to a variety of structural abnormalities. The most common cause of such deformations is uterine constraint. Between weeks 35 and 38 of gestation, rapid increase in the size of the fetus outpaces the growth of the uterus, and the relative amount of amniotic fluid (which normally acts as a cushion) also decreases. Thus, even the normal fetus is subjected to some degree of uterine constraint. However, several variables increase the likelihood of excessive compression of the fetus, including maternal conditions such as first pregnancy, small uterus, malformed (bicornuate) uterus, and leiomyomas. Causes relating to the fetus, such as presence of multiple fetuses, oligohydramnios, and abnormal fetal presentation, also may be involved."
Disruptions are also due to extrinsic disturbances, so the way FA formulates them leads to a bit of a misunderstanding. Deformation is the alteration of shape due to an extrinsic cause, like a misshapen bone. Disturbance is the destruction of a previously normally formed organ, due to an extrinsic cause again. Amniotic bands is the big example.
