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Stillbirth is often defined as fetal death after 20 weeks of gestation, but a fetus greater than any combination of 16, 20, 22, 24, or 28 weeks gestational age and 350g, 400g, 500g, or 1000g birth weight may be considered stillborn depending on local law. Once the fetus has died, the mother may or may not have contractions and undergo childbirth or in some cases, a Caesarean section. Most stillbirths occur in full-term pregnancies. The cause is often unknown.〔 In the U.S., the Born-Alive Infants Protection Act of 2002 specifies that any breathing, heartbeat, pulsating umbilical cord, or confirmed voluntary muscle movement indicate live birth rather than stillbirth.〔http://frwebgate.access.gpo.gov/cgi-bin/getdoc.cgi?dbname=107_cong_reports&docid=f:hr186.107〕 The term is often used in distinction to live birth (the baby was born alive, even if it died shortly thereafter) or miscarriage (early pregnancy loss). The word miscarriage is often used incorrectly to describe stillbirths. ==Causes== The causes of a large percentage of human stillbirths remain unknown, even in cases where extensive testing and autopsy have been performed. A rarely used term to describe these is "sudden antenatal death syndrome" or SADS, a phrase coined by Cacciatore & Collins in 2000. Many stillbirths occur at full term to apparently healthy mothers, and a postmortem evaluation reveals a cause of death in only about 40% of autopsied cases.〔Cacciatore, J. (2007). A phenomenological exploration of stillbirth and the effects of ritualization on maternal anxiety and depression, University of Nebraska-Lincoln Press, Digital Commons ; Froen, J.F. (2005).〕 In cases where the cause is known, some possibilities of the cause of death are: *bacterial infection *birth defects, especially pulmonary hypoplasia *chromosomal aberrations *growth retardation *Induced Fetal Demise *intrahepatic cholestasis of pregnancy *maternal diabetes *high blood pressure, including preeclampsia *maternal consumption of recreational drugs (such as alcohol, nicotine, etc.) or pharmaceutical drugs contraindicated in pregnancy *postdate pregnancy *placental abruptions *physical trauma *radiation poisoning *Rh disease *Female genital mutilation〔("Female genital mutilation and obstetric outcome: WHO collaborative prospective study in six African countries" ) Retrieved on 2012-2-22〕 *umbilical cord accidents * *''Prolapsed umbilical cord'' – Prolapse of the umbilical cord happens when the fetus is not in a correct position in the pelvis. Membranes rupture and the cord is pushed out through the cervix. When the fetus pushes on the cervix, the cord is compressed and blocks blood and oxygen flow to the fetus. The mother has approximately 10 minutes to get to a doctor before there is any harm done to the fetus. * *''Monoamniotic twins'' – These twins share the same placenta and the same amniotic sac and therefore can interfere with each other's umbilical cords. When entanglement of the cords is detected, it is highly recommended to deliver the fetuses as early as 31 weeks. * *''Umbilical cord length'' - A short umbilical cord (<30 cm) can affect the fetus in that fetal movements can cause cord compression, constriction and ruptures. A long umbilical cord (>72 cm) can affect the fetus depending on the way the fetus interacts with the cord. Some fetuses grasp the umbilical cord but it is yet unknown as to whether a fetus is strong enough to compress and stop blood flow through the cord. Also, an active fetus, one that frequently repositions itself in the uterus can cause entanglement with the cord. A hyperactive fetus should be evaluated with ultrasound to rule out cord entanglement. * *''Cord entanglement'' - The umbilical cord can wrap around an extremity, the body or the neck of the fetus. When the cord is wrapped around the neck of the fetus, it is called a nuchal cord. These entanglements can cause constriction of blood flow to the fetus. These entanglements can be visualized with ultrasound. * *''Torsion'' – This term refers to the twisting of the umbilical around itself. Torsion of the umbilical cord is very common (especially in equine stillbirths) but it is not a natural state of the umbilical cord. The umbilical cord can be untwisted at delivery. The average cord has 3 twists. After a stillbirth there is a 2.5% risk of another stillbirth in the next pregnancy (an increase from 0.4%). 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「stillbirth」の詳細全文を読む スポンサード リンク
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