Weight gain, compensating postural changes, and hormonally induced ligament laxity add to the woman’s predisposition toward pelvic misalignment/subluxation during pregnancy. This may lead to an elevated incidence of low back and hip pain, affecting quality of life and, potentially, the outcome of labor. These subluxations may also affect neurological function, which could affect the mother, development of the baby, and birthing outcomes.

In addition, the loss of neuromusculoskeletal integrity of the mother’s pelvic muscles and ligaments and its resulting effects on uterine support may cause an adverse condition known as intrauterine constraint, affecting infant positioning during pregnancy and birth.

Varney’s Midwifery text (1) states, “The potential for damage in pregnancy and the postpartum period to a woman’s neuromusculoskeletal structure is great. Shifts in the center of gravity forward and slightly upward destabilize her posture and realign the carriage of weights and forces through her joints, predisposing nerves, muscles, bones, and connective tissues to damage. Increased levels of relaxin and elastin further aggravate this situation.” Gait compensations and increased biomechanical loads lead to further sprain/strain on spinal segments and their supporting structures.

Female sacroiliac joints tend to be flatter, with a wider retroarticular space and longer interosseous ligaments, all of which promote greater mobility (2). As hormonal changes affect supporting musculature and increase ligament laxity, there is an increase in spinal and sacroiliac articulations compensation and mobility. If a motion segment is compensating for a lack of mobility at an adjacent level, then these segments may become hypermobile (3,4).

Maternal weight gain is most significant during this gestational period. This contributes largely to the profound biomechanical compromise of the lumbosacral spine. With a drastic shift in the gravitational weight bearing of the mother, pelvic musculoskeletal function—principally of the sacroiliac and hip joints—is imperiled. This leads to significant soft tissue structure changes such as hypertonicities or ligament laxity, which in turn creates biomechanical instability. Not just the lumbosacral spine but, to compensate, the thoracic and even cervical spines acquire a diversity of combinations of
aberrant segmental and global motion. The unfortunate typical short-radius sacral curve of later pregnancy provides the foundational imbalance for thoracic hyperkyphosis and cervical kypholordosis. Cellular edema and inflammation, with anatomical yielding of the intervertebral foraminae, generate neruropathology of the important spinal nerve tissues with resultant cellular and aggregate tissue malfunction. Pelvic misalignment is physiologically inherent to the last 3 months of pregnancy (5).

Cowlin (6) writes, “In the antepartal period, changes in posture occur gradually and can be responsible for a great many discomforts over the course of the pregnancy.” The prevalence of low back pain (LBP) during pregnancy can be as low as 42.5% (7) and as high as 90% (8), depending on the sample studied. One study revealed that 28% of women experienced back pain by the 12th week of gestation (9). Because of the biomechanical compensations discussed above, it is not unusual for pregnant women to experience pain in multiple areas of the spine, including sacral, lumbar, thoracic, cervical, and cranial. Borg-Stein and Dugan (10) write, “The specific anatomic and physiologic changes of pregnancy predispose to a specific set of diagnoses. Virtually all women experience some degree of musculoskeletal discomfort during pregnancy.”

LBP during pregnancy is a frequent clinical problem. In a sample of 200 women (11), 76% reported back pain at some time during pregnancy. Sixty-one percent reported an onset during the present pregnancy. Thirty percent with the highest pain scores reported great difficulties with normal activities (11). One survey reported the prevalence of LBP in pregnant women to be about 50% (12). The report stated that the most common reason for severe LBP during pregnancy was dysfunction of the sacroiliac joints (12).

It is important to confront the prevalence of back pain during pregnancy and the need to address these concerns without the harmful effects of drugs. The significance of this pain on the woman’s quality of life and function are sufficient reasons to establish safe and reliable models of care such as chiropractic (8,13,14,15,16).

Currently, most published research on chiropractic care during pregnancy addresses the efficacy of the adjustment for the resolution of LBP (17). One study (18) revealed that 75% of women who received chiropractic adjustments during their pregnancy stated that they experienced relief of their pain and discomfort. Two other studies (19,20) addressed the incidence of increased LBP during pregnancy and the positive results of spinal and pelvic adjustments. Another study (21) concluded that intensive adjustments are effective not only for the initial intensive care of LBP, but the authors also suggested that maintenance adjustments after initial intensive care may be beneficial to patients to maintain subjective disability levels after intensive care (21).

Another study (22) looked at back pain during both pregnancy and delivery with and without chiropractic care. The group of women who received chiropractic adjustments experienced less pain during labor. This study not only recommended adjustments for LBP during pregnancy, it recommended on-going maintenance care beyond the initial symptomatic, initial intensive care. Based on the results, the researchers concluded that “This study appears to confirm previous reports showing that LBP and disability scores are reduced after spinal manipulation. It also shows the positive effects of preventive chiropractic treatment in maintaining functional capacities and reducing the number and intensity of pain episodes after an acute phase of treatment” (23).

In past studies done on laboratory animals, a relationship between vertebral lesions in the lumbar area and interference to physiological function of that region were noted. It was also suggested that upper cervical lesions contributed to physiological disturbances in the mother, such as cardiac and thyroid malfunction and sexual disturbances. Of further interest was that lesions in these laboratory animals produced miscarriages, behavioral changes, premature births, stillbirth, “runty” offspring, and early death of the young. In human pregnancy, Burns (24,25) noted that women with vertebral lesions had pregnancies and labors that were abnormal compared with pregnant women without lesions. Further various obstetrical complications occurred with mothers suffering from lumbar lesions. Regarding the health of the developing young rabbits, the offspring of lesioned mothers demonstrated stunted growth, erratic behavior, slow development, and implications of anatomic deformities. Anrig recommended that additional studies are clearly warranted based on these results with animals (26).

Misalignment of the sacrum in the pregnant pelvis may be a contributing factor to musculoskeletal intrauterine constraint. Intrauterine constraint is defined as any forces external to the developing fetus that obstruct the
normal movement of the fetus (27). The putative association between a biomechanical dysfunction and subsequent intrauterine constraint may be via the uterine ligamentous attachments to the bony maternal pelvis. It is hypothesized that the torsion from the misaligned sacrum is transmitted to the uterus by the ligaments, creating an uneven muscular tension in the uterine walls. This uterine imbalance constricts fetal motion throughout pregnancy and, even more significantly, it has a direct effect on fetal positioning in preparation for and during the birth process. The uterus is supported by the broad ligament. From within the fascia of this ligament, the round and utero-sacral ligaments originate and attach to the pubic rami and sacrum, respectively. The combination of all of these ligamentous attachments contributes to support and positioning of the uterus. The broad ligaments are double layers of peritoneum extending from either side of the uterus to the lateral walls and floor of the pelvis. The thick base of the broad ligament is continuous with the connective tissue of the pelvic floor and is most responsible for proper uterine position and the prevention of uterine prolapse (28).

Each uterosacral ligament extends from an attachment posterolaterally to the supravaginal portion of the cervix, encircles the rectum, and inserts into the fascia over the second and third sacral vertebrae. The uterosacral ligaments are composed of connective tissue and some smooth muscle and are covered by peritoneum. They prevent the uterus from anterior and inferior displacement. It is proposed that sacral joint dysfunction and subsequent sacral rotation may transmit via the uterosacral ligament a unilateral force on to the uterus, torquing the uterus and resulting in a restricting tension within the uterine wall (28).

The round ligaments extend from the lateral, superior portion of the uterus toward the labium majus, inserting with the inguinal ligament within a fold of the peritoneum continuous with the broad ligament. They comprise smooth muscle cells directly continuous with those of the uterine wall and a certain amount of connective tissue. They prevent the uterus from moving posterior and keep it in a normal anterior position (28). It is proposed that unilateral tension in the round ligament may be caused by sacral dysfunction, with the resulting tension and imbalance of the uterus mentioned previously. Ruch (29) describes a variety of female complaints that can result from pelvic subluxation. Specifically, the broad ligament skews after ilia displacement, the result being tight and tender musculature on one side with uterine traction to one side (30).

Forrester and Anrig (30) stated, “specifically, sacral rotation causes an anterior torquing mechanism on the uterine ligaments and musculature, decreasing space and altering the environment for the fetus…when correction of the sacral subluxation occurs, the structure and therefore the function of the uterine structures are improved allowing the fetus to position itself properly.”

Intrauterine constraint contributes to abnormal fetal positioning during pregnancy and labor. Fetal presentations, other than cephalic or positions other than occiput anterior, may result in birth delay and complications for both mother and baby. According to Forrester and Anrig (30), intrauterine constraint may result in “the potential for a reduced efficiency in labor resulting in a longer, harder labor process with an increased incidence of anoxia, brain damage, asphyxia, prolapse of the umbilical cord, and intrauterine death, and a greatly elevated propensity toward operative delivery which exacerbates the danger of trauma to the neonate.”

Intrauterine constraint during pregnancy may cause irregular spinal development of the fetus as well. Compromised fetal positioning may affect spinal and nerve development in the fetus, with long-term risks for malfunction. Abnormal uterine constraint may be a cause of deformities in the upper cervical area, including the foramen magnum (31). Congenital torticollis in the newborn may be another sequela of compromised positioning and development in-utero.

Dystocia is broadly defined as abnormal function during labor and is the number one cause for invasive intervention during birth. It may lead to trauma and consequential subluxation in the mother and infant. It is important that the doctor of chiropractic understand the biomechanics of the pregnant female pelvis and its potential relationship to the neuromuscular causes of dystocia.

Williams Obstetrics (32) lists the causes of dystocia as

When examined from a neuro-muscular and biomechanical perspective, each of these causes of dystocia potentially may be prevented with specific chiropractic adjustments of the pregnant woman’s spine and pelvis throughout pregnancy and in preparation for birth.

Normal uterine muscle activity is imperative for the prevention of dystocia. Uterine dysfunction may be caused by a decrease in neurological impulses to the
uterus, which normally initiates strong contractions and maintains adequate muscle function throughout labor. Additionally, dilation of the cervix is dependant on normal nerve innervation. Spinal and cranial adjustments throughout pregnancy and during birth may facilitate adequate nerve impulses affecting uterine function (33,34,35,36).

Pelvic contraction is defined by William’s Obstetrics (30) as misalignment of the pelvic bones (particularly sacral displacement) caused by physical trauma to the woman. Specific chiropractic adjustments may offer the means for sacral and pelvic realignment, reducing the prevalence of sacral displacement, which can lead to dystocia.

Abnormalities of presentation, position, or development may be caused by intrauterine constraint. Preliminary studies with the Webster technique have suggested a musculoskeletal relationship between sacral adjustments, round ligament contacts, the alleviation of intrauterine constraint, and optimal fetal positioning. Optimal fetal positioning is a key ingredient in the prevention of dystocia (37,38,39,40,41,42,43,44,45,46,47,48

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