The results of this current study which showed that a high proportion of pregnant patients with LBP undergoing chiropractic treatment reported clinically relevant ‘improvement’ support those published in a recent cohort study as well as the recent randomized clinical trial (RCT) looking at chiropractic treatment for pregnant patients with low back or pelvic pain[16, 17]. The most recent systematic reviews of the literature for interventions for preventing and treating pelvic and back pain in pregnancy[5] and more specifically chiropractic treatment for these patients[4, 6] unanimously concluded that the available research evidence at that time was low to moderate quality at best. However, these reviews were published prior to the cohort study by Murphy et al. published in 2009[16] and the excellent RCT by George et al. published in 2013[17].

In the RCT by George et al. one treatment arm of the trial on pregnant women suffering from LB, PP or both included treatment by a chiropractor. The results clearly showed a statistically and clinically significant greater level of improvement for the patients who received the additional chiropractic treatment[17]. However, outcomes in that RCT were only measured at one time point between 5 and 9 weeks after the start of treatment and while the patients were still pregnant whereas this current study measured outcomes at 5 different and consistent time points during the pregnancy and after delivery. Comparing the baseline scores between this current cohort study with the baseline scores for the patients in the RCT who were treated with chiropractic shows that they were nearly identical, including the standard deviations (5.8 +/- 2.2 in the RCT, 6.07 +/- 1.91 in this current study). Additionally, the mean gestational weeks were also nearly identical in the two studies. Comparing the 1 month NRS pain scores in this current study with the NRS scores in the RCT measured between 5 and 9 weeks after the start of treatment for those patients in the treatment arm that received chiropractic treatment also shows that they are nearly identical. The NRS change score in the RCT was 2.9 and in this cohort study it was 3.06[17]. When looking at the mean NRS score at 3 months after the first treatment in this current study it is less than 1/3 of the original baseline score. However, approximately half of the patients would have delivered their babies by this 3 month data collection time point and this likely had a positive impact on this outcome. Therefore, although this cohort study is not a randomized clinical trial and thus the outcomes cannot be attributed to the chiropractic treatment, the strong similarity between these results and those from the recently published RCT supports their validity.

Comparing the outcomes from this study on Swiss patients with those from a very similarly designed outcomes study on patients in the United States (US)[16], shows that they are also quite similar. At 1 month after the start of treatment 70% of the patients in this current study reported clinically relevant improvement of ‘much better’ or ‘better’ compared to 73% of patients in the Murphy et al.[16] study. However, the precise time of their outcome data collection is not specified. It was done at the end of active treatment, and this time frame varied between patients. By 3 months after the start of treatment 85% of the patients in this current study reported being clinically significantly improved. It is important to point out that the option ‘slightly better’ on the PGIC scale was not considered clinically relevant improvement in this current study and these patients were classified as unchanged. Unfortunately it is not possible to compare disability scores or other quality of life factors between these two studies because the Murphy et al. paper used the Bournemouth questionnaire[16] whereas our current study used the Oswestry pain and disability questionnaire. The Bournemouth questionnaire would have been a better choice as an outcome measure for these types of patients as it measures more relevant domains, including psychosocial factors, compared to the Oswestry questionnaire. However, at the time that this current study was conducted the Bournemouth questionnaire was not yet translated and validated into German so could not be used whereas the Oswestry questionnaire had been translated and validated into both German and French.

Another relevant, although perhaps not surprising finding from this current cohort study includes the fact that patients who reported a higher number of previous LBP episodes (≥ 5) were less likely to report clinically relevant improvement, particularly at 1 year after the first treatment. However, this factor was not predictive in the logistic regression model. This is consistent with other studies that show that back pain is commonly recurrent[21–23]. However, the location category of the LBP (LB, PP, both) in this current study was not linked with the likelihood of improvement at any data collection time point nor in the logistic regression model. This is different from what Murphy et al.[16] found. They reported that patients with pain in both areas were significantly less likely to report clinically significant improvement in disability, at least in the short-term, compared to the other two groups. Furthermore, the majority of patients in the Murphy et al.[16] study had posterior pelvic pain (58.3%) whereas the location of the LBP in this current Swiss study was quite evenly distributed between the three locations, with approximately 1/3 of the patients reporting pelvic pain. Another difference between the Murphy et al.[16] study and this current one is that Swiss patients with a history of LBP during a previous pregnancy did not have worse outcomes compared to patients without LBP in a prior pregnancy whereas US patients without LBP in a previous pregnancy were more likely to report improvement compared to US patients with LBP in a previous pregnancy. Reasons for the differences in these outcomes between US and Swiss patients can only be speculated upon. Obesity is much more common in the US than in Switzerland and this may result in a higher proportion of women experiencing both LBP and pelvic pain during pregnancy as this could further increase the lumbar lordosis and place additional stresses on the pelvic joints[24].

The literature states that 94% of women who have LBP in a previous pregnancy have recurrent pain with subsequent pregnancies[23]. However, in this current cohort study only 58% of the patients who had experienced a previous pregnancy reported that they had suffered from back pain at that time. The reason for this discrepancy in proportions is unclear. It is also somewhat surprising that patients with more episodes of previous LBP have worse outcomes at the 1 week and 1 year time points but not at the 1, 3 and 6 month time points. Obviously at the 1 year data collection point all patients would have delivered their babies several months before and would likely then fall into the category of ‘usual’ low back pain patients where recurrence is not unusual.

No serious adverse events were reported in this study and over 85% of the patients were happy or very happy with their chiropractic treatment. Adverse events from spinal manipulation to pregnant women or those in the early post-partum period are very rare with only 7 cases found in the literature[25]. All seemed to be related to treating the cervical spine rather than the low back however, and the practitioners involved included chiropractors, a physiotherapist, and a general medical practitioner. A recent qualitative study evaluating the treatment experience of pregnant women under chiropractic care reported that chiropractors’ approach to these patients is patient-centered rather than symptom centered[26]. This may explain why such a high percentage of the patients in this current study were happy with their treatment.

Some of the limitations to this study have been alluded to above. Because this is a cohort study without a control group or other treatment group for comparison, the outcomes reported cannot be assumed to arise from the treatment. Additionally, the patients in this study were treated primarily at two practice sites but by different chiropractors and the details of the types of treatments and treatment dosage are not known. No attempt was made to compare outcomes by practitioner or style of treatment. This would be interesting for future studies. As previously stated, the use of the Oswestry questionnaire was not the best choice for this patient population, but was the best available that was translated and validated in both German and French. Additionally, the assessment of symphysis pubis pain in these pregnant patients was not specifically assessed as it was desired to use those same categories of low back pain in pregnancy that previous papers used in order to make direct comparisons.