Rates in various medical conditions
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 myopathy 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%
Atresia 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%
Leiomyoma 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%.Also, women with previous Caesarean deliveries have a risk of breech presentation at term twice that of women with previous vaginal deliveries.The highest possible probability of breech presentation of 50% indicates that breech presentation is a consequence of random filling of the intrauterine space, with the same probability of breech and cephalic presentation in a longitudinally elongated uterus. Types
Types of breech depend on how the babys legs are lying.
Twisting the body such that an arm trails behind the shoulder, it will tend to cross down over the face to a position where it can be reached by the obstetricians finger, and brought to a position below the head. A similar rotation in the opposite direction is made to deliver the other arm. In order to present the smallest diameter (9.5 cm) to the pelvis, the babys head must be flexed (chin to chest). If the head is in a deflexed position, the risk of entrapment is increased. Uterine contractions and maternal muscle tone encourage the head to flex. Oxygen deprivation may occur from either cord prolapse or prolonged compression of the cord during birth, as in head entrapment. If oxygen deprivation is prolonged, it may cause permanent neurological damage (for instance, cerebral palsy) or death. It has been suggested that a fast vaginal delivery would mean the risk of stopping babys oxygen supply is reduced. However, there is not enough research to show this and a quick delivery might cause more harm to the baby than a conservative approach to the birth.Injury to the brain and skull may occur due to the rapid passage of the babys head through the mothers pelvis. This causes rapid decompression of the babys head. In contrast, a baby going through labor in the head-down position usually experiences gradual molding (temporary reshaping of the skull) over the course of a few hours.