Premature Breech Fetus
Vaginal delivery poses special problems for premature breech babies weighing less than 3.5 to 4 pounds. The main concern is that, on average, the baby's head is somewhat larger in diameter than its buttocks or abdomen. In a breech birth, the birth canal is dilated first by the buttocks and abdomen. Delivery of the head may be delayed while the birth canal dilates further to accommodate its larger size. This may also cause compression of the immature head, leading to brain injury. Moderate to severe delay in the delivery of the baby's head is known as head entrapment. During this delay, the umbilical cord (which connects the baby's navel to the placenta) may be squeezed between the baby's head and the birth canal, blocking the baby's blood supply, possibly resulting in oxygen deprivation. The baby's spine or other structures may also be damaged through birth trauma. For these reasons, cesarean section is usually the best delivery option for premature breech babies.
There have never been any properly designed studies to determine which delivery method is best for breech babies weighing less than 3.5 to 4 pounds, though there is considerable evidence to suggest that babies between 3.5 and 5.5 pounds (typically 32 to 36 weeks along in the pregnancy) may, in selected cases, be delivered vaginally by experienced obstetricians. Experts agree, however, that before attempting vaginal delivery, the same conditions required for term or near-term breech vaginal delivery must be met.