Approximately 3% to 4% of all pregnancies reach term (38-plus weeks of gestation) with a fetus in the breech presentation, in which the baby’s rear end is introduced before the head. Breech presentation is common when remote from term. However, as term approaches, the uterine cavity most often accommodates the fetus in a longitudinal lie, with head presentation. Predisposing factors for breech presentation are preterm (early) deliveries, excessive amount of amniotic fluid, fibroids, malformations of the fetus or uterus, high parity leading to uterine relaxation, multiple fetuses, abnormal implantation of the placenta on the cervix, and previous breech presentation.
In a complete breech position, the breech comes first with bent knees; in a frank breech, the lower extremities are flexed at the hips and extended at the knees, with feet near the head; the term footling breech applies when the feet enter the birth canal ahead of any other part of the body. Diagnosis of breech presentation can be made by abdominal palpation, when the hard, round head is felt in the upper uterus, and the feeling of small parts or the breech by vaginal examination and confirmed by ultrasound. Breech presentation places a fetus at increased risk for adverse outcome, including morbidity and mortality from difficult delivery, low birth weight due to preterm delivery (before 36 weeks gestation), prolapse of the umbilical cord, and fetal anomalies.
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Discussion and planning for the mode of delivery should ideally take place well before admission to labor and delivery as essential differences exist between labor in head and breech presentations. Undoubtedly, cesarean delivery is preferred when the presentation is footling, the fetus is compromised or large, or has a congenital abnormality that could cause a mechanical problem at vaginal delivery, or when a clinician experienced in vaginal breech delivery is not available. Nevertheless, there is a general consensus that the outcome for the singleton baby is improved by planned caesarean section compared with planned vaginal delivery in any of the breech conditions. In head presentation, the body follows rapidly after the delivery of the fetal head, whereas an infant who arrives breech-first risks having its head stuck in the birth canal because the body does not stretch the birth canal wide enough for the head to pass through. Indeed, spontaneous expulsion of the fetus at breech presentation is seldom accomplished, and assistance of the obstetrician is required. Also, delivery of the breech draws the umbilical cord into the pelvis, which leads to cord compression. This can cause fetal distress, leading to morbidity.
Recently, in a randomized study comparing modes of delivery for breech presentation, neonatal mortality and serious neonatal morbidity were significantly lower for the planned cesarean section group than for the planned vaginal birth group. There were no differences between groups in terms of maternal mortality or serious maternal morbidity.
Most women wish to avoid cesarean section because it is not a risk-free procedure. External cephalic version is the only effective and basically safe intervention to convert a breech fetus to vertex presentation with the potential to help women avoid operations. It is performed exclusively through the abdominal wall by gentle pushing on the abdomen while viewing fetal movement with real-time ultrasound. The buttocks are elevated from the birth canal and grasped laterally, while the fetal head is directed toward the pelvis. Uterine relaxation, induced by certain drugs, is sometimes recommended before the procedure. Fetal heart rate monitoring is performed before and after the external version for assessment of fetal well-being. The risk for urgent cesarean delivery for fetal distress following external version is less than 1%. Studies of external cephalic version at term report a success rate of above 60%. Determinants of unsuccessful version include uterine contractions, diminished amount of amniotic fluid, maternal obesity, and prior descent of the breech into the birth canal.
- The American Academy of Family Physicians, http://www.aafp.org
- Cheng, M., & Hannah, M. E. (1993). Breech delivery at term: A critical review of the literature. Obstetrics and Gynecology, 82, 605–618.
- Hannah, E., Hannah, W. J., Hewson, S. A., Hodnett E. D., Saigal S., & Willan, A. R. (2000). Planned caesarean section versus planned vaginal birth for breech presentation at term: A randomized multicenter trial. Term Breech Trial Collaborative Group. Lancet, 356, 1375–1383.