A breech birth is the birth of a baby delivered buttocks- or feet-first rather than in the typical head-first orientation. Around 3–4% of pregnant women at full-term (37–40 weeks pregnant) have a breech baby. Due to their higher than average rate of possible complications for the baby, breech births are generally considered higher risk. Breech births also occur in many other mammals such as dogs and horses (see veterinary obstetrics).
Most babies in the breech position are delivered via caesarean section because it is seen as safer than being born vaginally. Doctors and midwives in the developing world often lack the equipment or disposable hospital resources required to safely assist women giving birth to a breech baby vaginally. Also, delivering all breech babies by caesarean section in developing countries is difficult to implement as there are not always resources available to provide this service.
Cause With regard to the fetal presentation during pregnancy, three periods have been distinguished.
During the first period, which lasts until the 24th gestational week, the incidence of a longitudinal lie increases, with equal proportions of breech or cephalic presentations from 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, 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 presentations during this period.
In the third period, from the 36th gestational week onward, the incidence of cephalic and breech presentations remain stable, i.e. breech presentation around 3–4% and cephalic presentation approximately 95%. In the general population, incidence of breech presentation at preterm corresponds to the incidence of breech presentation when birth occurs.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.
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.
The incidence of breech presentation is affected by both maternal and fetal diseases and medical conditions. When these factors are present, the probability of breech presentation is between 4% and 50%.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.
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 baby's legs are lying.
A frank breech (otherwise known as an extended breech) is where the baby's legs are up next to their abdomen, with their knees straight and their feet next to their ears. This is the most common type of breech. A complete breech (or flexed breech) is when the baby appears as though they are sitting crossed-legged with their legs bent at the hips and knees. A footling breech is when one or both of the baby's feet are born first instead of the pelvis. This is more common in babies born prematurely or before their due date. A kneeling breech is when the baby is born knees first.
In addition to the above, breech births in which the sacrum is the fetal denominator can be classified by the position of a fetus. Thus sacro-anterior, sacro-transverse and sacro-posterior positions all exist but left sacro-anterior is the most common presentation. Sacro-anterior indicates an easier delivery compared to other forms.
Complications Umbilical cord prolapse may occur, particularly in the complete, footling, or kneeling breech. This is caused by the lowermost parts of the baby not completely filling the space of the dilated cervix. When the waters break the amniotic sac, it is possible for the umbilical cord to drop down and become compressed. This complication severely diminishes oxygen flow to the baby, so the baby needs to be delivered immediately so that they can breathe. In these circumstances a caesarean section is likely to be recommended. If there is a delay in delivery, the brain can be damaged. 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)—in simplest terms, the size of the hips is 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 baby's body to emerge while the cervix has not dilated enough for the head to emerge.
Because the umbilical cord—the baby's 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. 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 obstetrician's 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 baby's 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 baby's 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 baby's head through the mother's pelvis. This causes rapid decompression of the baby's 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. This sudden compression and decompression in breech birth may cause no problems at all, but it can injure the brain. This injury is more likely in preterm babies. The fetal head may be controlled by a special two-handed grip called the Mauriceau–Smellie–Veit maneuver or the elective application of forceps. This will be of value in controlling the rate of delivery of the head and reducing decompression. Related to potential head trauma, researchers have identified a relationship between breech birth and autism.
Squeezing the baby's abdomen can damage internal organs. Positioning the baby incorrectly while using forceps to deliver the after coming head can damage the spine or spinal cord. It is important for the birth attendant to be knowledgeable, skilled, and experienced with all variations of breech birth.
Factors influencing safety
Birth attendant's skill (and experience with breech birth) – The skill of the doctor or midwife and the number of breech births previously assisted is of crucial importance. Many of the dangers in vaginal birth for breech babies come from mistakes made by birth attendants. With the majority of breech babies being delivered by cesarean section, there is more risk that birth attendants will lose their skills in delivering breech babies and therefore increase the risk of harm to the baby during vaginal delivery. Type of breech presentation – the frank breech has the most favorable outcomes in a vaginal birth, with many studies suggesting no difference in outcome compared to head-down babies. (Some studies, however, find that planned caesarean sections for all breech babies improve outcome. The difference may rest in part on the skill of the doctors who delivered babies in different studies.) Complete breech presentation is the next most favorable position, but these babies sometimes shift and become footling breeches during labour. Footling and kneeling breeches have a higher risk of cord prolapse and head entrapment.