Home > Gynecology, Research Methodology, Uncategorized > When conclusions don’t tell the whole story, and on paracervical blocks for IUDs

When conclusions don’t tell the whole story, and on paracervical blocks for IUDs

I recently was looking into whether or not you should place a paracervical block before placing an intrauterine device, after a particular patient had a difficult time with a placement.   Over my career, I generally haven’t done so, as the vast majority of patients don’t seem to have a significant amount of pain, and the literature I have read has not been very supportive of the practice.

Today I looked at the literature again, and was a little irritated at what I found.  One particular study was Mody et al, which concluded “Compared with no anesthetic, a 1% lidocaine paracervical block did not result in a statistically significant decrease in perceived pain with IUD insertion.”

So clearly most would read this and say that it doesn’t matter if you put in a paracervical block or not.

But’s here’s the kicker;  the summary of their data is the following: ” Twenty-six women received the paracervical block before IUD insertion, and 24 received no local anesthesia. Groups were similar in age, parity, ethnicity, education and complications. Women who received the paracervical block reported a median VAS score of 24.0 mm with IUD insertion, and women who did not receive local anesthetic reported a median VAS score of 62.0 mm with IUD insertion; p=.09.”

So patients who got a block had pain of 2 on a scale of 2 to 10, and patinets who did not have a block had pain of 6 on the same scale.  So did the paracervical block really not work?
I would say it did.  What didn’t work was the study, or at least most likely so.   The p value, or likelihood that the outcome was do to statistical chance alone, was 0.09. In translation, there was a 9% chance that the difference between the groups was due to chance alone, and a 91% chance that it was due to an actual effect of the paracervical block.  Since we arbitrarily say that a p of 0.05 is statistically significant, the authors say that the study was negative.

But isn’t this quite misleading?  It is 10 to 1 likely that the paracervical block actually made the procedure less painful, and we just didn’t reach a p of < 0.05 because there weren’t enough patients in the study to adequately separate the groups mathematically (lack of power).

P values are important, but we can’t consider them to be everything.  Statistical significance is a continuous variable, not a nominal one.  If we say that p=0.049 means that the study shows a difference and p=0.051 means there was no difference, we are just being foolish, and in the end quite ignorant of the actual mathematics that goes into how the p value was created.

Here’s how I would like to see such a study concluded : “Compared with no anesthetic, a 1% lidocaine paracervical block showed a strong trend towards decreasing pain with IUD insertion, that did not reach statistical significance.  Further study with a greater number of patients is warranted.”

If you read their conclusion, you would probably take from that that paracervical blocks don’t work.  But if you read mine, you take a different message, which is actually supported by the data, which would be “It is very likely that paracervical blocks decrease pain with IUD insertion”, which of course makes sense

Mody SK; Kiley J; Rademaker A; Gawron L; Stika C; Hammon C.  Pain control for intrauterine device insertion: a randomized trial of 1% lidocaine paracervical block. Contraception. 2012; 86(6): 704-9.

 

  1. Ella
    May 16, 2016 at 4:31 pm

    Thank you. I was one of those patients who had an immense amount of pain from the IUD insertion (8 on the pain scale, involuntary sweating and muscle spasms, pain overwhelmed my ability to think). I am also a statistician, and the magnitude of the difference in the study combined with the small sample makes me agree with your conclusion.

    Of course, I am a statistician, so I’m also aware that my own experience is creating a very strong prior towards believing that an anesthetic would help. But I don’t think this bias is overwhelming for my analysis, even if it is definitely biasing me towards commenting that this is an issue I want to see studied more.

    I understand that IUDs have only relatively recently been recommended for nulliparous women in the US, of which I am one. I’ve seen anecdotes that this might matter for pain. I wonder if (hypothesize that) this might be an important factor to control for, and that it has biased the field towards believing that substantial pain is unusual for all women.

    You can google IUD insertion pain and find a large number of stories from women who found the procedure excruciating. So I know I’m not alone, although not how uncommon I am. For all that, it was worth it to not have to deal with birth control nor periods. I just wish the doctor had been upfront that it might hurt a lot (or that the field knew if I was an outlier!). “Discomfort” does not begin to describe my experience.

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  2. Dilipa Magnusson
    October 12, 2016 at 6:30 am

    There is a study from Turkey where a paracervical block was compared to saline injection and no intervention. There was a significant difference observed between the actual block compared to the saline and no intervention. The difference was dramatic enough to be what you expect from an intervention that actually works to reduce patient pain. Somebody working in the medical field could probably do better at picking the study apart.

    The study:
    Cırık, D. A., Taşkın, E. A., Tuğlu, A., Ortaç, A. S., & Dai, Ö. Paracervical block with 1% lidocaine for pain control during intrauterine device insertion: A prospective, single-blinded,
    controlled study. Int J Reprod Contracept Obstet Gynecol 2013, 2, 263–7.

    DOI:
    10.5455/2320-1770.ijrcog20130902

    Full access URL:
    http://www.ejmanager.com/mnstemps/89/89-1369676520.pdf?t=1476222741

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