A breech birth occurs when a baby is born bottom first instead of head first. Around 3-5% of pregnant women at term (37–40 weeks pregnant) will have a breech baby.

Most babies in the breech position are born by a caesarean section because it is seen as safer than being born vaginally.

As most breech babies are delivered by caesarean section in developed countries, doctors and midwives may lose the skills required to safely assist women giving birth to a breech baby vaginally. Delivering all breech babies by caesarean section in developing countries may be very difficult to implement or even impossible as there are not always resources available to provide this service.

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%.

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.