Cesarean, mortality, and the law of diminishing returns

At first glance, the graph above appears to represent an indictment of contemporary obstetric practice. From 1970-1980, the C-section rate rose precipitously, and the neonatal mortality rate also dropped precipitously. Since then, the C-section rate has continued to rise ever faster, but neonatal mortality, although continuing, has declined at ever slower rates. Yet this is exactly what we would predict if the C-section rate were following the law of diminishing returns.

According to Wikipedia, the law of diminishing returns (also known as the law of marginal utility) means:

… in a production system with fixed and variable inputs (say factory size and labor), there will be a point beyond which each additional unit of the variable input (i.e., man-hours) yields smaller and smaller increases in outputs, also reducing each worker’s mean productivity. Conversely, producing one more unit of output will cost increasingly more (owing to the major amount of variable inputs being used, to little effect).

In the case of Cesarean sections, the law of diminishing returns would predict that there will be a point beyond which each addition increase in C-section rate yields smaller and smaller decreases in neonatal mortality rate.

Imagine a hypothetical first world country that has 1 million births per year. In this hypothetical country, we are able to analyze the number of lives saved by C-sections and we are able to analyze it in hindsight so that we know which C-sections were necessary. As the C-section rate rises, the numbers of lives saved drops off (diminishing returns). In our hypothetical country, we can chart how many lives are saved for each percentage point of the C-section rate. Each percentage point of the C-section rate represents 10,000 C-sections. Our chart might look something like this:

C-section rate lives saved/10,000 C-sections
0-5%% 20,000 (every mother and baby)
6-10% 10,000 (every baby)
11-15% 5,000
16-20% 500
21-25% 50
26-30% 5
31-35% 0.5
36-40% 0.05

We can see the law of diminishing returns in action here. At a C-section rate from 0-5%, every C-section is necessary, and every C-section saves the life of both mother and baby. From 6-10% every C-section is necessary and saves the life of the baby. From 11-15% half the C-sections are necessary, resulting in a savings of 5000 lives. At rates higher than 15%, retrospective analysis reveals that far fewer C-sections are life saving. By the time a C-section rate of 35-40% is reached, only one additional baby will be saved every other year.

The results can be expressed another way. We can determine retrospectively how many C-sections were unnecessary. Here’s that chart:

C-section rate unnecessary C-sections/10,000
0-5% 0
6-10% 0
11-15% 5,000
16-20% 9,500
21-25% 9,950
26-30% 9,995
31-35% 9.999.5
36-40% 9,999.05

So the law of diminishing returns tells us that, beyond a certain point, we will have to do more C-sections to save one neonatal life. In other words, beyond a certain point, we will have to do more unnecessary (in retrospect) C-sections for each life we save.

Of course, that tells us about C-sections in the aggregate, but the decision to perform a C-section is made on a case by case basis. Moreover, in court, the decision to find an obstetrician guilty of malpractice for not performing a C-section is also made on a case by case basis. The parents and the court really don’t care how many unnecessary C-sections you have to do to save one baby, if that baby is their baby.

Yet the C-section rate can be too high. When you get to the point that you are saving 1 baby every 10 years, the C-section rate is clearly too high. However, a tremendous premium is placed on the life of each and every baby. That societal value is reflected in the fact that our judicial system operates as if we believe that if a C-section had even a remote chance of preventing the death or disability, that C-section should have been done, and because it wasn’t done, the parents should be compensated.

The above graph represents what we appear to believe about the value of the life of each baby. Personally, I think the standard should be different. The number of unnecessary C-sections done to save one baby every decade should not be unlimited. The standard for determining fault in an obstetric malpractice case should not be to show that a C-section “might” have prevented a baby’s death or disability; the standard should be that the doctor could have reasonably foreseen (based on the evidence available) that a C-section was necessary to prevent the baby’s death or disability.

C-sections come with costs. We have not even talked about the financial costs, because, in my judgment, these are secondary. However, very large numbers of unnecessary C-sections will result in unnecessary complications and unnecessary deaths. If the C-section rate continues to rise, these unnecessary complications and unnecessary deaths will increase from relatively uncommon occurrences, to occurrences that far outweight the number of babies’ lives saved.

We, as a society, need to think about where we draw the line, because we, as a society, through our punishments and incentives, determine how high the C-section rate should be. The graph above is not an indictment of obstetrics. It is a warning to us to consider what we truly value. Do we really believe that it is worth any number of C-sections to save one baby’s life? We certainly act as though we do.