Pelvic alignment changes during the perinatal period

Background
The function of the pelvic bones is to transfer load generated by body weight. Proper function of the pelvic bones can be disturbed by alignment changes that occur during pregnancy. Further, misalignment of the pelvic bones can lead to pain, urinary incontinence, and other complications. An understanding of the timing and nature of pelvic alignment changes during pregnancy may aid in preventing and treating these complications.
Objective
To investigate the changes in pelvic alignment during pregnancy and one month after childbirth.
Methods
This is a prospective, longitudinal cohort study. Pelvic measurements were obtained for 201 women at 12, 24, 30, and 36 weeks of pregnancy, and 1 month after childbirth. The anterior and posterior width of the pelvis (the distance between the bilateral anterior superior iliac spines and the bilateral posterior superior iliac spines), the anterior pelvic tilt, and pelvic asymmetry (the mean left and right pelvic tilt degrees and the bilateral difference of the anterior pelvic tilt) were measured. For the change in pelvic alignment, a Friedman test was conducted to determine any significant difference in the measurements over time.
Results
The anterior and posterior width of the pelvis became significantly wider with pregnancy progress and the anterior width of the pelvis at 1 month after childbirth remained wider than that at 12 weeks of pregnancy (p < 0.001). The anterior pelvic tilt increased during pregnancy and decreased after childbirth (p < 0.05).
Conclusion
Some changes in pelvic alignment occur continuously during the perinatal period. Changes in the anterior width of the pelvis are not recovered at one month post-childbirth. Understanding these perinatal changes may help clinicians avert complications due to pelvic misalignment.

背景
骨盆骨（pelvic bones）的功能是传递体重所产生的负荷。孕期发生的骨盆排列改变可能会干扰其正常功能。此外，骨盆排列异常可引发疼痛、尿失禁（urinary incontinence）及其他并发症。明晰孕期骨盆排列改变的时机与特征，有助于预防和治疗此类并发症。
研究目的
本研究旨在探究孕期及产后1个月内的骨盆排列变化。
研究方法
本研究为前瞻性纵向队列研究（prospective longitudinal cohort study）。招募201名孕妇，分别于妊娠12、24、30、36周及产后1个月进行骨盆测量。测量指标包括骨盆前后宽度（双侧髂前上棘与双侧髂后上棘之间的距离）、骨盆前倾角度，以及骨盆不对称性（左右骨盆前倾角度的均值与骨盆前倾角度的双侧差值）。针对骨盆排列的动态变化，采用Friedman检验（Friedman test）分析不同时间点测量值的统计学差异。
研究结果
随着妊娠进展，骨盆前后宽度显著增宽；产后1个月时的骨盆前宽度仍显著宽于妊娠12周时的测量值（p < 0.001）。骨盆前倾角度在孕期逐渐升高，产后则出现下降（p < 0.05）。
研究结论
围产期（perinatal period）内骨盆排列会出现一系列持续性的动态变化。产后1个月时，骨盆前宽度的改变并未完全恢复至孕前水平。明晰此类围产期变化，可帮助临床医生有效规避因骨盆排列异常引发的各类并发症。