Wednesday, October 31, 2007

New BMJ study shockingly misleading

Around the world newspapers are blaring headlines like "Vain C-sections kill more babies" ( and the perenial favorite "Too posh to push" (The Telegraph, UK) in reporting about a study published in the BMJ today, Maternal and neonatal individual risks associated with cesarean delivery: multicentre prospective trial. The study shows nothing of the kind. There is not even a single woman in the study who had a cesarean without a medical reason.

According to the authors:
Women undergoing caesarean deliveries, either intrapartum or elective ... had double the risk for severe maternal morbidity and mortality (including death, hysterectomy, blood transfusion, and admission to intensive care) and up to five times the risk of a postpartum infection compared with
women undergoing vaginal delivery. Though caesarean delivery carries almost no risk of severe vaginal complications and a slightly reduced risk of intrapartum fetal death, in cephalic presentation it is significantly associated with an increased risk of severe neonatal morbidity and mortality, independent of fetal distress and gestational age. With breech presentation, caesarean delivery substantially reduces the risk to the baby ...
Based on the newspaper headlines you might be forgiven for the thinking that the study actually SHOWED that maternal request C-section resulted in higher rates or maternal or neonatal mortality or morbidity, but it showed nothing of the kind. In fact, it didn't even examine the issue. Based on the conclusion of the study itself, you might be forgiven for thinking that the study showed that elective C-sections resulted in higher maternal or neonatal mortality or morbidity. It doesn't show that either. Why? Because the authors chose to call all non-emergency cesareans (regardless of the medical indication) "elective". They never even looked at maternal request cesareans or medically unindicated cesareans.

The authors studied more than 94,307 births in Latin America. Of these, 66% were vaginal deliveries and 34% were cesarean sections. The authors classified cesarean deliveries as follows:
Caesarean deliveries were classified as elective if the operation was decided by the attending staff before the onset of labour and the woman was referred either from an antenatal clinic or a high risk ward to the delivery unit for caesarean delivery regardless of the diagnosis... Intrapartum caesarean delivery was when a caesarean was indicated during labour, whether labour was spontaneous or induced.

We excluded emergency caesarean delivery without labour, which denoted women referred for a caesarean before onset of labour with the diagnosis of acute severe fetal distress, severe vaginal bleeding, uterine rupture, maternal death with a living fetus, eclampsia, or any other diagnosis considered by the attending staff to require emergency elective caesarean delivery.
You might think that "elective" cesarean means cesarean by choice without a medical reason. That's not what it means here. In this study, "elective" cesearan means cesarean done for a pre-existing medical condition or pre-existing pregnancy complications that was not expected to result in imminent death. An intrapartum cesarean, in contrast, was any cesarean done for a reason that developed during labor.

Just look at Table 1, Characteristics of study population according to mode of delivery to see what this means. Among the 13,208 "elective" cesareans:

repeat C-section 46.1%
breech 14.2%
pre-existing medical conditions 9%
complication of current pregnancy 40.2%

When you add it up, the number is more than 100% because some women had more than one medical indication for cesarean. As far as the data shows, there was not even a single woman who had a cesarean with out a medical indication! There were no elective cesareans, there group that was labeled "elective" should have been labeled "non-emergent".

As the authors themselves acknowledge:
... the [elective] caesarean group had higher risk in terms of women with previous complicated pregnancies or perinatal outcomes, problems related to current pregnancy, and being referred from other institutions for delivery...
The bottom line is that this is a study comparing women who had vaginal deliveries with women who had MEDICALLY indicated cesarean sections, both non-emergent and emergent. It never investigated elective cesareans and therefore it reaches no conclusions about elective cesareans.

What are the real conclusions of the study:

Women undergoing MEDICALLY INDICATED caesarean deliveries, either non-emergent or emergent, had slightly increased rates of maternal death (vaginal delivery 11 per 100,000; non-emergency cesarean 38 per 100,000; emergency cesarean 61 per 100,000). The difference between maternal death rates for vaginal delivery and non-emergency cesarean is not statistically significant. There was no significant difference in the need for blood transfusions among the 3 groups. There was a slightly increased risk of ICU admission for both cesarean groups and a significantly increased risk of hysterectomy among both cesarean groups.

Cesarean reduced the risk of peripartum death. There was a slight decrease for babies in the cephalic presentation and a much more marked decrease for breech babies. Cesarean section lowered the risk of neonatal death and of prolonged NICU stay for breech babies. The rate of neonatal mortality and prolonged NICU stay was slightly higher in the cesarean groups, but that is not suprising since these babies were delivered by cesarean reasons precisely because there were medical indications.

The bottom line: cesarean section reduced the risk of neonatal death, particularly for breech babies. There was a slightly increased risk of maternal death in women undergoing emergency cesarean, but there was no significant difference in maternal death between vaginal delivery and non-emergency medical indicated cesarean.

0 Old Comments: