Prenatal diagnosis is of concern in families at risk for recurrence of OI where there is a risk for the birth of an affected child because of parental germline mosaicism, or in a family affected with an autosomal dominant form of OI. Four techniques are used at present for prenatal diagnosis. High-resolution ultrasound scan of fetal limb length and morphology can reliably identify fetuses with type II OI by 14-16 weeks' gestation, and some fetuses with the progressive deforming variety of OI (type III) by 18-20 weeks' gestation. In the absence of fracture or significant bowing, ultrasound cannot be used to identify fetuses with the milder forms of OI, even in families with a positive history of OI. If mutant type I collagen has been identified in cultured fibroblasts from an affected parent or child, then mesenchymal cells cultured from chorionic vilus biopsies taken at about 10-11 weeks' gestation, which synthesize collagen comparable to dermal fibroblasts, can be used for diagnostic studies. Because OI represents a private mutation in most families, mutational analysis of DNA from chorionic vilus or amniotic fluid cells can be used only in pregnancies where the molecular defect has been previously identified. In large families, linkage studies may identify the gene and the allele, which contain the mutant sequence, thus permitting prenatal diagnosis by haplotype analysis of fetal DNA and can be used in pregnancies at risk for all types of OI.
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The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.