Musculoskeletal pain is a common occurrence during pregnancy and the postpartum period. For example, low back pain has been reported to occur as frequently as 50% to 85% of pregnant women [1–4] and at two to three years postpartum, eight to 20% of these women still report persistent symptoms [5, 6]. Although low back pain is often accepted as an unavoidable complaint during pregnancy, for some women the pain can be debilitating, interfering with sleep, work and normal activities of daily living [7, 8]. However, the etiology of this pain is unknown . It has been suggested that low back pain experienced during pregnancy is multifactoral in nature and some of the proposed mechanisms include, but are not limited to, the influence of altered circulating relaxin levels producing ligamentous laxity [7, 10], maternal weight gain and/or biomechanical changes due to pregnancy .
In the non-pregnant population, low back pain is a significant cause of pain and disability as well, with 80% of the population experiencing an episode during their lifetime [7, 11]. Neck pain [12, 13] and headaches  are also a substantial source of pain and disability in the non-pregnant population . One of the effective treatment options used by manual practitioners for those suffering from low back pain [15, 16] cervical spine [16, 17] and some headache pain [18, 19] is spinal manipulative therapy (SMT). SMT is usually characterized as a localized force of high velocity and low amplitude directed at a spinal segment . Severe adverse effects of SMT are rare in the cervical spine [20–22] and lumbar spine .
Manual treatment options for pregnancy-induced pain, such as back pain, have been reported to be limited . However, chiropractors report seeing pregnant patients frequently, and surveys of chiropractors reflect an opinion that SMT is safe for pregnant patients [1, 24]. While the safety of SMT for adult and pediatric populations has undergone scrutiny in both public and scientific domains [13, 22, 25], the safety of SMT in sub-groups of the population including pregnant and postpartum patients has received little attention. This lack of evidence is surprising given the obvious importance of the welfare of the expectant and new mother. Given the hormonal and the coagulability status of peripartum and postpartum individuals, it is possible that SMT is a contraindication to the musculoskeletal complaints associated with pregnancy.
It is accepted that females are more susceptible to increases in joint laxity than men [26–28]. Hormonal causes have been postulated as a potential source for this increase in female joint laxity [29–32]. Relaxin, a polypeptide that is produced by the corpus luteum during pregnancy , is one of the implicated hormones. In the pregnant female, relaxin is essential in order to secure the passage of the fetus during parturition in several animal species ; it has been associated with a decrease in soft tissue tension especially in preparing the female body for delivery including relaxing the pelvic ligaments, inhibiting spontaneous uterine contractions, ripening of the uterine cervix, and stimulating the mammary glands . Although relaxin increases laxity in the symphysis pubis in preparation for birth, its effects are not solely limited to that joint. In addition, women immediately postpartum are thought to also have this hormone-mediated ligament laxity that might reduce the protective stability of the intervertebral articulations .
Hypercoaguable disorders that promote thrombosis have been categorized as thrombophilias . During pregnancy and the postpartum state the risk of thrombophilia increases compared to the non-pregnant state [36, 37]. Thromboembolism or pulmonary embolism has been identified as the leading cause of maternal death in the United States [36, 37]. These hypercoaguable disorders during pregnancy can be a result of venous stasis, changes in the vessel wall and changes in the composition of blood; also known as Virchow's triad .
In the absence of a prospective study of the safety of SMT during the antepartum and postpartum periods, it would be beneficial to survey the scientific literature for the number and types of injuries sustained by pregnant and postpartum patients following spinal manipulation. While systematic reviews of the literature on the use of SMT for pregnancy and related conditions have been conducted [1, 11], an exploration of the literature specifically for adverse events associated with SMT and pregnancy has not yet been undertaken. Accordingly, the aim of this study is to critically review the literature for reported cases of iatrogenic injuries following spinal manipulative therapy during the pregnancy and postpartum periods.