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Lightning strikes, shark bites & uterine rupture

When someone understates the risk of UR, I think it’s just as important the clarify as it is when someone overstates the risk. How else are women to make an informed decision? Just as it’s plain wrong for an OB to tell a woman with one prior low transverse cesarean that she has a 20% risk of rupture, it’s equally wrong when VBAC advocates say the risk is virtually non-existent.

Over the years, I have heard the statement:

You are more likely to be struck by lightning or bitten by a shark than experience uterine rupture!

Today I’m going to get the statistics and run the numbers so you can see for yourself how the risk of these events compare.

Uterine Rupture

For this exercise, we will use the uterine rupture (UR) rate based on one prior low transverse (bikini) cut cesarean in a spontaneous labor determined by Maternal and Perinatal Outcomes Associated with a Trial of Labor after Prior Cesarean Delivery (Landon 2004):

Risk of uterine rupture: 1/240 or 0.4%
Risk of infant death or oxygen deprivation: 1/2000 or 0.05%

Lightning Strikes

Using the faulty theory I’m going to calculate the number of Floridians, since it is the “lightning strike state,” who would be struck by lightning.

Let’s assume that the risk of getting struck by lightning in Florida is the same as uterine rupture (even though the saying goes the risk is greater): 1 in 240 or 0.4% or 0.00416

With 18,328,340 people living in Florida, that would mean that 76,368 people are struck by lightning every year in Florida. According to the CDC, that is more than the number of Americans who die annually from diabetes (72,449), Alzheimer’s disease (72,432), and influenza and pneumonia (56,326).

Using the National Weather Service stat that 10% of people struck by lightning die, we would have 7,636 people dying in Florida every year from lightning strikes. At that rate, you would have 209 people struck by lightning and 20 of those people dying every day in the state of Florida.

Now, I don’t live in Florida and I’m not an expert in lightning strikes, but that sounds like a lot of people dying.

Now let’s switch our assumptions and use the National Weather Service’s stats.

Odds of being struck by lightning in a given year (reported deaths + injuries) 1/700,000
Odds of being struck by lightning in a given year (estimated total deaths + injuries) 1/400,000

When we turn that fraction into a percentage, we get the following risk of being struck by lightening: 0.00025% – 0.00014%.

Using the National Weather Service’s statistics, we get 26 – 46 annual lightning strike related deaths or injuries in Florida.

Which sounds more reasonable to you? 26-46 Floridians struck annually by lightning or 76,368?

And that is assuming that the rate is the SAME as uterine rupture, but the rumor is that the rate of lightning strikes is HIGHER which means MORE than 76,368 Floridians are struck by lightning every year and more than 20 Floridians are dying daily from lightning strikes.

Now, does that pass the smell test? Does it seem reasonable in the least? It doesn’t to me.

Some would argue that in order to make the comparison, we need to eliminate the number of non-birthing people in Florida, but you really don’t because the lightning strike doesn’t know whether you are a man, woman, child, or menopausal. A Floridian women with one prior cesarean in spontaneous labor has the same risk as everyone else to be struck by lightning: 0.00025% – 0.00014%.

Shark Bites

From the Florida Museum of Natural History:

What are the chances of being attacked by a shark?

The chances of being attacked by a shark are very small compared to other animal attacks, natural disasters, and ocean-side dangers. Many more people drown in the ocean every year than are bitten by sharks. The few attacks that occur every year are an excellent indication that sharks do not feed on humans and that most attacks are simply due to mistaken identity. For more information on the relative risk of shark attacks to humans click HERE.

How many people are attacked each year by sharks?

Worldwide there is an average of 50-70 shark attacks every year. The number of attacks has been increasing over the decades as a result of increased human populations and the use of the oceans for recreational activity. As long as humans continue to enter the sharks’ environment, there will be shark attacks. For more information on shark attack statistics click HERE.

We have about 6.5 billion people on the world and 50-70 get bit by a shark annually which works out to 0.00000077% – 0.00000108%.

But this whole discussion is moot because it’s poor statistics to even compare these events (UR & lightning strikes or shark bites) because they are totally different types of occurrences.

The Actual Figures

This is a great chart from the Floria Museum of Natural History website entitled “A Comparison of Unprovoked Shark Attacks with the Number of Lightning Fatalities in Coastal United States: 1959-2008” where they show even in the state of Florida, over the past 49 years, there have been a mere 453 lightning fatalities and 585 shark bites. Remember that over 7,600 Floridans would be dying annually if the rate of uterine rupture was the same as the rate of lightning strikes.

Comparing Risks

There are some major problems when one is trying to compare risks of differing events.

One problem is when one uses a lifetime risk statistic as a means for comparison. You simply cannot take a statistic, like your lifetime risk of being struck by lightning (1 in 5000 which is significantly lower than one’s annual risk,) and compare that to your one-time risk of uterine rupture. If anything, using the annual risk of lightning strikes would be more accurate, but it still would be a false comparison.

An article by Andrew Pleasant entitled, Communicating statistics and risk, elaborates:

An oft-reported estimate is the lifetime breast cancer rate among women. This rate varies around the world from roughly three per cent to over 14 per cent.

In the United States, 12.7 per cent of women will develop breast cancer at some point in their lives. This statistic is often reported as, “one in eight women will get breast cancer”. But many readers will not understand their actual risk from this. For example, over 80 per cent of American women mistakenly believe that one in eight women will be diagnosed with breast cancer each year.

Using the statistic ‘one in eight’ makes a strong headline but can dramatically misrepresent individual breast cancer risk.

Throughout her life, a woman’s actual risk of breast cancer varies for many reasons, and is rarely ever actually one in eight. For instance, in the United States 0.43 per cent of women aged 30–39 (1 in 233) are diagnosed with breast cancer. In women aged 60–69, the rate is 3.65 per cent (1 in 27).

Journalists may report only the aggregate lifetime risk of one in eight because they are short of space. But such reporting incorrectly assumes that readers are uninterested in, or can’t comprehend, the underlying statistics. It is critically important to find a way, through words or graphics, to report as complete a picture as possible.

Take away message: Be extra careful to ensure your readers understand that a general population estimate of risk, exposure or probability may not accurately describe individual situations. Also, provide the important information that explains variation in individual risk. This might include age, diet, literacy level, location, education level, income, race and ethnicity, and a host of other genetic and lifestyle factors.

The second major problem is often the two things you are comparing are so different that the comparison is worthless. Again, I defer to Mr. Pleasant:

Try not to compare unlike risks. For instance, the all-too-often-used comparison ‘you’re more likely to be hit by a bus / have a road accident than to…’ will generally fail to inform people about the risks they are facing because the situations being compared are so different. When people assess risks and make decisions, they usually consider how much control they have over the risk. Driving is a voluntary risk that people feel (correctly or not) that they can control. This is distinctly different from an invisible contamination of a food product or being bitten by a malaria-carrying mosquito.

Comparing the risk of a non-communicable disease, for example diabetes or heart disease, to a communicable disease like HIV/AIDS or leprosy, is similarly inappropriate. The mechanisms of the diseases are different, and the varying social and cultural views of each makes the comparison a risky communication strategy.

Take away message: Compare different risks sparingly and with great caution because you cannot control how your audiences will interpret your use of metaphor.

Going Forward

It can be hard when wading through the (mis)information available on the internet about VBAC, but here are some tips to help you out.

1. Always find the source – If you find some great statistic, but there is no source referenced, be wary.

2. Verify the statistic – If there is a source listed, read through it. If there is no source listed, do a quick Google search. It didn’t take me long at all to find all the statistics in this article and run the math.

3. Leave a comment – If you find something on the internet that doesn’t pass the smell test, leave a comment on the blog or email the author asking for the source.

4. Be careful about forwarding things – There is so much misinformation on the internet, so do your friends a favor and don’t forward them emails or articles unless you have verified the information to be true. That is one way to quickly nip falsehoods in the bud!

For further reading on using statistics, check out, Correlation and Causation:Misuse and Misconception of Statistical Facts and Risk Communication, Risk Statistics, and Risk Comparisons: A Manual for Plant Managers

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14 comments to Lightning strikes, shark bites & uterine rupture

  • Great post, Jen! A great point of caution. I’ve seen this email many times. I’ve highlighted your post on the ICAN blog’s weekly feature “Best of the Birth Blogs” for this week (ending 8/23): http://ican-online.org/community/users/ican-blog/blog/best-birth-blogs-week-ending-august-23rd

    All best,
    Sarah

  • Yes, great post! I’ve seen these things stated so many times and have never taken the time to look up the stats on this information–thank you for doing so! You’re right: misinformation is terrible no matter which way one looks at it.

  • [...] Yet since the ACOG guidelines came out in 2004, more and more hospitals have refused to do VBACs. Today, nearly half of hospitals won’t do VBACs, either because the hospital has banned them or because doctors won’t do them.  WHY?? All this for a less than 1% chance that something could go wrong. And what does a less than 1% chance mean exactly? [...]

  • mumofar

    i just found this website but have been reading through different posts. i must say, i love you!
    it is hard to find someone so balanced! i spent the whole day the other day being bullied by a bunch of extremists homebirthers who refused to believe any pro-hospital statistics and then had their own completly unsubtatntiated claims that they kept trying to force down my throat.
    so, I am completely thrilled to find someone who is supportive of VBACs, realistic about the risks and able to comprehend that not all stats are equal and a critical mind must be used when approaching them. there’s so much work to do to look through the vast piles of information in this area and it’s so nice to have someone, and a website like this, to help!
    you are my hero!! xxxxxxx

  • Melanie

    Remember C-section is VERY dr freindly…
    No waiting, no watch and see, no teing up a bed for hours while nature takes its course…and yes they can be home for dinner.

    I may sound a bit sarcastic, but it is true…

  • KoryO

    Melanie….really? Is that the BEST you got??? You obviously can’t argue with logic, since you don’t address any of the points made here, and your attempt to baffle with BS is a D-. And I’m a generous grader.

    See, I was one of those so-called nonexistent UR cases that Jen is talking about here. I had only one prior c-section, and was not induced to start labor. If there was a poster girl for VBAC, that would have been me. It all went beautifully until the last couple of minutes. Then all hell broke loose. (I’m guessing that you have never been on the patient end of a UR. I hope you never are. It was the most frightening thing I have ever experienced, bar none. I was on the table for two hours getting sewn up, and I lost 2 liters of blood.)

    If my doctors were really THAT into getting home for dinner, I don’t know why they would have “let me go” from 3 am to 5 pm in my TOLAC. On a Friday. I mean, not only did they miss dinner, they also missed happy hour….and in a university town, you don’t wanna miss happy hour on Friday.

    Which reminds me….the next time I’m there, I’ll buy those doctors a round. It’s the least I owe them for saving me and my baby girl.

  • Stephanie

    I love this….excellent! *applauds* well done!

    My second biggest complaints (after the misrepresentation of statistics) is this: choosing a repeat elective cesarean doesn’t just eliminate the existing risk of a uterine rupture, it trades it for the risks of a cesarean (which are rarely discussed when talking about VBACs) It also drives me crazy when people act like “low risk” means “no risk”.
    “I am 22 and my baby had Down Syndrome!” Being at a lower risk doesn’t make you at no risk. Even if the risk WERE the same as being struck by lightening…doesn’t mean you won’t be struck by lightening! The reason we have those statistics is because it does, indeed, happen to some people. (no matter how much you put your head into the sand)

    Good job…good post…thank you for this!!

  • Kate

    Thanks for that, it would also be helpful to break down the ‘rupture’ risks; things like the difference between classical scars and lower segment ones, the increased risk if the scar is compromised by a low placenta, the difference made by induction (even ‘natural’ methods) and the fundamental distinction between a harmless and symptom-free scar separation and a true rupture where mum or baby are in danger. Rupture happens to mums without scars, or with scars from other surgeries too, but they are never frightened with those risks by their care providers, even when the outcomes are often less positive than for a lower transverse section scar that separates!
    I had a catastrophic rupture – at 33 weeks pregnant, long before any scheduled CS date… Trouble is, the first section, the one that led to the VBAC/Repeat CS debate in the first place, WAS for surgeon convenience and so he could finish his shift and go home… He admitted as much to the OR nurse as he was sewing me up, ‘Well that’s the last one delivered, time to pack up and we can all go home,’ he said. Not me, I couldn’t just go home, I couldn’t even lift my baby!
    Yes, I am grateful to the surgical team for saving us when I ruptured, losing more than half my body’s blood volume, putting us both in ITU, but nothing like as angry as I am with the one who just didn’t want to hang around until I was ready to birth my baby, probably in the middle of the night instead of the more civilised 8pm when he decided to do a section for ‘slow progress’ – note not no progress, not baby stuck or either of us in trouble, but just too slow for his comfort!
    I’d rather punch that man in the face rather than buy him a drink. Without that surgeon-led section I would never even have been at risk from a ruptured scar. VBAC is more dangerous, but the biggest problem is that so many primary sections are not necessary, or at least are preventable earlier in labour, and enormous numbers of women are being exposed to a risk of VBAC (even if it is a very low risk) or the risks of repeat major surgery (which are probably higher than the risk of rupture) with out any good cause at all…

    • Jen Kamel

      Hi Kate!

      Yes, getting that primary cesarean rate down would greatly impact our total cesarean rate in addition to making women safer in future labors. But I wouldn’t argue that VBAC is more dangerous than a repeat cesarean. They both offer risks and benefits and it comes down to which set of risks are acceptable to you. As I said in “A father asks why invite the risk of VBAC:”

      VBACs can absolutely be offered safely without 24/7 anesthesia present. All it takes is a motivated staff that acknowledges that while the risk of infant death or oxygen deprivation in VBACs is 0.05%, the maternal mortality in repeat cesareans is 0.04% (Landon, 2004). Whose lives do we save? And in fact Henci Goer’s analysis shares with us that the 0.05% rate is inaccurately elevated. In the Landon (2004) study, women whose babies had died before labor were encouraged to VBAC. Those infant deaths were included in the 0.05% figure even though their deaths could not be attributed to a labor after cesarean. (For more information, please Henci’s analysis.)

      Warmly,

      Jen

  • Cindy B

    Very good argument about statistics… just to give you a Floridian’s perspective… the percentages might even be lower because most of us joke that those hit by lightning are often tourists/non-natives (not that it’s really funny) because we know to get inside when there’s a storm. So, if you add in all the tourists into the numbers and divide by the actual number of people being struck… I’m sure you come out with a smaller percentage. I love math, btw ;)

  • diana west

    Kate, excellent point!! Prevention!! I had my first section because of “failure to progress and baby not engaged”. My question? Why the heck induce me at 37 wks in the first place, then?? I should have been sent home. But had i done my homework and been better informed, i would have saved myself the headache and definitely the heartache that came with my failed vbac.

  • Kory, I’m so sorry for your UR. I don’t know if you’ll ever come back here and see this. I also had a UR. My conditions weren’t as favorable as yours. Four prior cesareans, undiagnosed severe uterine septum (which can cause UR) placental abruption (which can cause UR and be caused by a septum) possible pre-e (which can cause placental abruption and UR.) As the doula, I’ve attended VBACs and RCS, but I know first hand the horrors of dying on the OR table and loosing your only son. Still, I absolutely recognize that it is true that MOST DOCTORS want the easiest and most clear cut way to delivery, and will push cesarean even if a VBAC is statistically safer for that patient. I know women who have HAD successful VBACs and then pushed toward cesarean because of this. Some hospitals have a near 100% or 100% cesarean rate for this reason (that is not an exaggeration by any means.) There are also some doctors who are absolutely concerned about the patient’s desires, and recognize the risks in cesarean and do not blow risk out of proportion, recognizing there are risks and benefits to all delivery choices. They may even do VBA3 or 4C and are highly criticized by their peers. They buck the system, risking their own reputation, and possibly their medical license, to ensure their patients get a chance at the birth they desire and deserve. To those doctors not willing to cower, I applaud them. Again, I’m so sorry about your rupture, I hope your little girl has no lasting effects from the rupture. I understand the feelings you convey in your comment, I don’t think anyone believes that UR is non existent, and to the families touched by rupture it’s all too real. Often VBAC hopefuls don’t want to hear stories like ours but they really NEED to. It doesn’t help anyone going into a birth choice without fully understanding the risks. The same goes for RCS moms.