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A breech birth is the birth of a baby from a breech presentation, in which the baby exits the pelvis with the buttocks or feet first as opposed to the normal head-first presentation. In breech presentation, fetal heart sounds are heard just above the umbilicus. The bottom-down position presents some hazards to the baby during the process of birth, and the mode of delivery (vaginal versus Caesarean) is controversial in the fields of obstetrics and midwifery. Though vaginal birth is possible for the breech baby, certain fetal and maternal factors influence the safety of vaginal breech birth. The majority of breech babies born in the United States are delivered by Caesarean section as studies have shown increased risks of morbidity and mortality for vaginal breech delivery, and most hospital policies do not permit vaginal breech birth for this reason. As a result of reduced numbers of vaginal breech deliveries, most obstetricians do not receive training in the skill set required for safe vaginal breech delivery anymore. ==Cause== With regard to the fetal presentation during human gestation, three periods have been distinguished. During first period which lasts until the 24th gestational week, the incidence of a longitudinal lie (see ) increases with the equal proportion of a breech and cephalic presentation within this lie. This period is characterized by frequent changes of presentations. The fetuses in breech presentation during this period have the same probability for breech and cephalic presentation at delivery. During the second period, lasting from the 25th to the 35th gestational week, the incidence of cephalic presentation increases during the second period with a proportional decrease of breech presentation. The second period is characterized by a higher than random probability that the fetal presentation during this period will also be present at the time of delivery. The increase of this probability is gradual and identical for breech and cephalic presentation during this period. In the third period from the 36th gestational week onward, the incidence of cephalic and breech presentation remain stable, i.e. breech presentation around 3-4% and cephalic presentation approximately 95%. In general population, incidence of breech presentation at preterm birth corresponds to incidence of breech presentation for this particular period of gestation when birth occurs.〔Miller EC, Kouam L. Frequency of breech presentation during pregnancy and on full term. Zentralbl Gynakol 1981;103:105–109.〕〔Hill L. Prevalence of Breech Presentation by Gestational Age. American Journal of Perinatology 2008; 7: 92–93.〕〔Hughey MJ. Fetal position during pregnancy. Am J Obstet Gynecol 1985;153:885–886.〕〔Sørensen T, Hasch E, Lange AP. Fetal presentation during pregnancy. Lancet 1979;2:477.〕〔Tadmor OP, Rabinowitz R, Alon L, Mostoslavky V, Aboulafia Y. Can breech presentation at birth be predicted from ultrasound examination during the second or third trimester? Int J Gynaecol Obstet 1994;46:11–14.〕〔Boos R, Hendrik HJ, Schmidt W. Behavior of fetal position in the second half of pregnancy in labor with breech and vertex presentations. Geburtshilfe Frauenheilkd 1987;47:341–345.〕〔Witkop CT, Zhang J, Sun W, Troendle J. Natural history of fetal position during pregnancy and risk of nonvertex delivery. Obstet Gynecol 2008;111:875–880.〕 A breech presentation at delivery occurs when the fetus does not turn to a cephalic presentation. This failure to change presentation can result from endogenous and exogenous factors. Endogenous factors involve fetal inability to adequately move, whereas exogenous factors refer to insufficient intrauterine space available for fetal movements.〔Sekulić S, Zarkov M, Slankamenac P, Bozić K, Vejnović T, Novakov-Mikić A. Decreased expression of the righting reflex and locomotor movements in breech-presenting newborns in the first days of life. Early Hum Dev. 2009; 85: 263-6.〕 Incidence of breech presentation among diseases and medical conditions with the incidence of breech presentation higher than that occurs in the general population, shows that the probability of breech presentation is between 4% and 50%. These data are related to: 1. single series of medical entities; 2. collections of series for some particular medical entity; 3. data obtained from repeated observations under the same conditions; 4. series of two concomitant medical conditions. Incidence of breech presentation at delivery in various medical conditions and diseases: FETAL ENTITIES: First twin 17-30%; Second twin 28-39%; Stillborn 26%; Prader-Willi syndrome 50%, Werdnig-Hoffman syndrome 10%; Smith-Lemli-Opitz syndrome 40%; Fetal alcohol syndrome 40%; Potter anomaly 36%; Zellweger syndrome 27%; Myotonic dystrophy 21%, 13 trisomy syndrome 12%; 18 trisomy syndrome 43%; 21 trisomy syndrome 5%; de Lange syndrome 10%; Anencephalus 6-18%, Spina bifida 20-30%; Congenital Hydrocephalus 24-37%; Osteogenesis imperfecta 33.3%; Amyoplasia 33.3%; Achondrogenesis 33.3%; Amelia 50%; Craniosynostosis 8%; Sacral agenesis 30.4%; Arthrogriposis multiplex congenita 33.3; Congenital dislocation of the hip 33.3%; Hereditary sensory neuropathy type III 25%; Centronuclear myoptathy 16.7%; Multiple pituitary hormone deficiency 50%; Isolated pituitary hormone deficiency 20%; Ectopic posterior pituitary gland 33.3%; Congenital bilateral perisilvian syndrome 33.3; Symmetric fetal growth restriction 40%; Asymmetric fetal growth restriction 40%; Nonimmune hydrops fetalis 15%; Atresio ani 18.2%; Microcephalus 15.4%; Omphalocele 12.5%; Prematurity 40% PLACENTAL AND AMNIOTIC FLUID ENTITIES: Amniotic sheet perpendicular to the placenta 50%; Cornual-fundal implantation of the placenta 30%; Placenta previa 12.5%; Oligohydramnios 17%; Polyhydramnios 15.8%; MATERNAL ENTITIES: Uterus arcuatus 22.6%; Uterus unicornuatus 33.3%; Uterus bicornuatus 34.8%; Uterus didelphys 30-41%; Uterus septus 45.8%; Leimyoma uteri 9-20%; Spinal cord injury 10%; Carriers of Duchenne muscular dystrophy 17% COMBINATION OF TWO MEDICAL ENTITIES: First twin in uterus with two bodies 14.29%; Second twin in uterus with two bodies 18.52%.〔Braun FH, Jones KL, Smith DW. Breech presentation as an indicator of fetal abnormality. J Pediatr. 1975; 86: 419-21.〕〔Sekulić SR, Mikov A, Petrović DS. Probability of breech presentation and its significance. J Matern Fetal Neonatal Med. 2010;23(10):1160-4.〕 As well, women with previous cesarean deliveries have a risk of breech presentation at term twice that of women with previous vaginal deliveries.〔Vendittelli, F., Rivière, O., Crenn-Hébert, C., Rozan, M. A., Maria, B., Jacquetin, B. (May 2008). "Is a breech presentation at term more frequent in women with a history of cesarean delivery?". American Journal of Obstetrics and Gynecology 198 (5): 521.e1–6. doi:10.1016/j.ajog.2007.11.009. PMID 18241817〕 The highest possible probability of breech presentation of 50% indicates that breech presentation is a consequence of at random filling of the intrauterine space, with the same probability of breech and cephalic presentation in a longitudinally elongated uterus.〔Sekulić SR, Petrović DS, Runić R, Williams M, Vejnović TR. Does a probability of breech presentation of more than 50% exist among diseases and medical conditions? Twin Res Hum Genet. 2007; 10:649-54.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Breech birth」の詳細全文を読む スポンサード リンク
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