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DALLAS, TX -- The more obese a pregnant woman is at the time
of delivery, the more likely she will deliver her baby by
Cesarean section, according to a study by obstetric
anesthesiologists at Duke University Medical Center.

Because of this, the researchers recommend that all obese
women who come to a hospital in labor should consider having an
epidural analgesia line placed in order to minimize the
potential risks of general anesthesia if a C-section becomes
necessary. An epidural involves the placement of a thin
catheter into the epidural space near the spinal column, which
allows physicians to introduce anesthetic agents that can be
used to block the pain of vaginal delivery or provide
anesthesia for a C-section. In a general anesthetic, the
patient is unconscious; when an epidural is used, the patient
is awake but cannot feel pain in the lower half of the
body.

Anesthesiologists in most cases don't see expectant mothers
until just a few hours before delivery, but the type of
anesthesia used can directly affect the health of mother and
baby. This is especially true of obese women, because
physicians encounter more difficulty in successfully
administering emergency general anesthesia to overweight
patients.

Duke obstetric anesthesiologist Dr. Elizabeth Bell prepared
the results of her study for presentation Monday (Oct. 12) at
the annual meeting of the American Society of
Anesthesiologists.

Bell reviewed the medical records of 2,493 mothers who gave
birth at Duke University Hospital and whose height and weight
was taken over a 16-month period, and found that 833, or one
third, received a C-section. Then she calculated each patient's
body mass index (BMI), which is considered the most reliable
measurement of obesity, for all the mothers.

"We found that the patients who had C-sections had an
average BMI of 53, significantly higher than the average BMI of
31 for those delivering vaginally," Bell said. "Just as
importantly, the more obese a patient was at the time of
delivery, the more likely she was to have a C-section."

The study was funded by Duke's Division of Women's
Anesthesia, which maintains a comprehensive database of all
obstetric anesthesic cases at Duke.

"Since we as anesthesiologists are rarely involved in the
care of mothers during the course of their pregnancy, we need
to be able to make the appropriate anesthetic decision, usually
at the last minute," Bell said. "Very large people can be
difficult to put under general anesthesia."

When administering general anesthesia, physicians must
insert a tube through the voice box into the windpipe which
will maintain an open breathing passage for the patient while
she is unconscious. To accomplish this, physicians must first
administer drugs which in effect "paralyze" patients so they
will accept the tube without gagging.

"All pregnant women experience water gains in mucosal
tissues and tongue, which makes them swell and prone to
bleeding," she explained. "In very large women this problem is
amplified, so it can be difficult to place the tube in the
right place."

If it then turns out that physicians are unable to place the
tube, the patients are still under the influence of the drugs
and are unable to take care of themselves until the drugs wear
off. The timing is especially critical if the baby is in
distress, Bell said.

"Every minute that passes that the baby is not delivered can
lead to potential health problems for the baby," she said.

This is complicated by the fact that since the baby pushes
the diaphragm upward as it grows, pregnant women are more prone
to acid reflux from the stomach, which can come up the throat
and down into the lungs. This effect is also amplified in the
obese.

In terms of actual pounds, the average weight of women in
the study who had a C-section was 191 pounds, the average of
vaginal delivery was 182.

"Weight alone isn't the best way to compare people, since
obviously a tall person may weigh more than a short person
without being obese," Bell said. "The BMI corrects for the
three-dimensional nature of weight, and it is simple,
non-invasive and inexpensive."

BMI, because it takes into account the height of a person,
is considered a more accurate measure of obesity, Bell said. It
is calculated by dividing body weight by the square of the
height. In the general population, a BMI of 30 is considered
obese and 35 is considered morbidly obese.

A corresponding definition of obesity for pregnant women has
not been determined, Bell said. As an example, a patient who is
5'4" weighing 175 pounds would have a BMI of 30.