Rather simple principles apply for the role of mechanical factors in morphogenesis. These are that the direction and magnitude of forces affect the form of the developing individual, as illustrated in Fig. 51-1 . Some of the factors that affect…
Genesis The underlying mechanism for most defects related to problems associated with obstetric procedures is vascular disruption. With chorionic villus sampling (CVS), removal of villi may result in embryonic hypotension, hypoxia, endothelial damage, hemorrhage, and necrosis with tissue loss. Defects…
Genesis Constraint that occurs during the latter period of gestation can cause molded deformations with good prospects for spontaneous or assisted return to normal form; however, when constraint occurs during early morphogenesis, it can have more severe and lasting impacts…
Genesis Ectopic pregnancy , defined as the implantation of a fertilized ovum outside the uterus, occurs most commonly in the fallopian tube (95.5% of all ectopic pregnancies), with 70% implanting in the ampulla, 12% in the isthmus, 11% in the…
Genesis Fetal movement is essential to normal joint morphogenesis. Joints develop secondarily within the condensed mesenchyme of the developing bones, and chronic lack of movement leads to joint contractures. Fetal akinesia is associated with a specific combination of clinical findings…
Genesis The relative and absolute amount of amniotic fluid tends to decrease during the last trimester as the fetus fills out the uterine cavity, as shown in Fig. 46-1 . A serious deficiency of amniotic fluid will result in significant…
Genesis Several different types of problems can limit the size and/or shape of the uterus and thus enhance the likelihood of fetal deformation. Examples include a malformed uterus caused by failure of the Müllerian ducts to completely fuse during embryogenesis,…
Genesis In face and brow presentations, the face is the compressed presenting part, usually with extension of the head ( Fig. 44-1 ). Face presentation occurs in 1 to 2 per 1250 deliveries, and persistent brow presentation is less common.…
Genesis Transverse lie is the second most common non-vertex presentation and occurs in 12 per 1000 deliveries. It is associated with multiparity (90%), prematurity (13%), placenta previa (11%), polyhydramnios (8%), uterine anomalies (8%), and uterine myomas (3%), especially when myomas…
Genesis The frequency of singleton breech presentation at term is 3.1% and rises to 6.2% when multiple births are included. Breech presentation is an important cause of deformation, and fully one third of all deformations occur in babies who have…