Among full-term, head-down babies, cord prolapse is quite rare, occurring in 0.4 percent. Among frank breech babies the incidence is 0.5 percent, among complete breeches 5 percent, and among footling breeches 15 percent.Head entrapment is caused by the failure of the fetal head to negotiate the maternal midpelvis. At full term, the fetal bitrochanteric diameter (the distance between the outer points of the hips) is about the same as the biparietal diameter (the transverse diameter of the skull)—simply put the size of the hips are the same as the size of the head. The relatively larger buttocks dilate the cervix as effectively as the head does in the typical head-down presentation. In contrast, the relative head size of a preterm baby is greater than the fetal buttocks. If the baby is preterm, it may be possible for the babys body to emerge while the cervix has not dilated enough for the head to emerge. Because the umbilical cord—the babys oxygen supply—is significantly compressed while the head is in the pelvis during a breech birth, it is important that the delivery of the aftercoming fetal head not be delayed. If the arm is extended alongside the head, delivery will not occur. If this occurs, the Løvset manoeuvre may be employed, or the arm may be manually brought to a position in front of the chest. The Løvset manoeuvre involves rotating the fetal body by holding the fetal pelvis.
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.