Chapter 9: Birth Defects & Prenatal Diagnosis

Birth Defects & Prenatal Diagnosis begins by classifying structural anomalies into specific categories such as malformations, disruptions, deformations, and syndromes, noting that while many defects have genetic or environmental causes, the majority are multifactorial in origin. A significant portion of the text details the principles of teratology, emphasizing that susceptibility to teratogens depends on the genotype of the conceptus, the specific mechanism of action, the dose and duration of exposure, and most critically, the stage of development, with the period of organogenesis (weeks three to eight) being the most sensitive time for inducing major structural defects. The summary extensively covers various environmental factors known to be teratogenic, including infectious agents like the Zika virus, which causes severe microcephaly, as well as Rubella, Cytomegalovirus, and Toxoplasmosis. It examines physical agents such as ionizing radiation and hyperthermia, alongside a wide array of pharmaceutical and chemical agents. Specific attention is given to the disastrous effects of thalidomide on limb formation, the craniofacial defects caused by isotretinoin (Vitamin A) and anticonvulsants like valproic acid, and the risks associated with SSRIs, opioids, and warfarin. The chapter also analyzes the impact of social drugs, detailing Fetal Alcohol Spectrum Disorder (FAS) and the risks of smoking and illicit drug use, as well as maternal metabolic conditions like diabetes, obesity, and phenylketonuria (PKU). Finally, the text shifts to perinatology and the tools available for prenatal diagnosis, explaining the utility of ultrasonography for assessing fetal age and nuchal translucency, maternal serum screening for alpha-fetoprotein (AFP), and invasive procedures such as amniocentesis, chorionic villus sampling (CVS), and cordocentesis. It concludes with an overview of noninvasive prenatal screening (NIPS) using cell-free fetal DNA and the emerging field of fetal therapy, including intrauterine blood transfusions and open or fetoscopic surgery to repair defects like spina bifida and diaphragmatic hernias.