by Dr. Elliot Berlin, DC
Have you heard of pelvimetry? Hopefully not. Pelvimetry is the process of clinical examination and/or imagery such as x-ray, CT scan or MRI to determine whether or not a pelvis has adequate space for a baby to pass through during labor and delivery. If the clinician determines that a pelvis is ‘too small’ or not of ideal shape or that a baby is ‘too large’ (cephalo-pelvic disproportion) they may recommend early induction or cesarean birth.
However, there is a pelvic paradox. In practice, we see small babies sometimes have trouble moving through a relatively large pelvis whereas a large baby may navigate smoothly through a small pelvis without complication. Similarly, one study concluded that for head down babies there is not enough evidence to support the use of pelvimetry for deciding mode of delivery. That while women who undergo pelvimetry may be more likely to have a cesarean section, it did not significantly improve birth outcomes for the mother or baby. [https://www.ncbi.nlm.nih.gov/pubmed/28358979]
Another study concluded that “pelvimetry does not change management of pregnant patients. Current practice is to allow all women a trial of labor regardless of pelvimetry results. This makes the routine performance and recording of clinical pelvimetry a waste of time, a potential liability, and an unnecessary discomfort for patients.” [https://www.ncbi.nlm.nih.gov/pubmed/15243832]
While modern methods of imaging can provide very clear pictures and measurements of pelvic size and shape and ultrasound can give us a ballpark idea of whether a baby is on the smaller or larger size, neither of them can determine functionality. By way of analogy, imagine the unborn baby as a basketball and the pelvis through which they have to pass as a rubber band. The basketball is bigger than the rubberband; sometimes significantly so. However, the bones of the baby’s head are not fused together before birth. It’s as if the basketball is underinflated and therefore able to compress and mold its way through a smaller space. The pelvis is a series of bones connected by ligaments and cartilage that functionally acts like a rubber band which can expand to allow a larger object to pass through and then contract back to its original shape and size.
Pelvimetry has no way of measuring functionality. At the end of pregnancy hormonal changes work to loosen the pelvis and make it more accomodating of the baby’s positioning and movements before and during birth. However, muscles and tendons around the pelvis can be stiff or tight and the joints between the bones of the pelvis can become restricted. These types of dysfunction make the pelvis more like a rigid rubber band that may resist the movements of the baby rather than accommodating or facilitating them.
Understanding perinatal musculoskeletal functionality provides insight into the pelvic paradox. This is also why in our practice we work to improve pelvic function before birth. We utilize a combination of clinical massage and bodywork to identify and release restricted muscles and tendons in the low back, hips and pelvis and chiropractic analysis and adjustments to restore function to restricted joints and ligaments. We recommend home exercises to further improve spinal and pelvic mobility. I employ the same techniques when called to a birth where fetal positioning isn't ideal or a baby isn’t moving down through the pelvis.
In this episode of ‘The Real Midwives of Los Angeles’ a petite laboring mom named Sarah gives birth to a nearly 11 pound baby vaginally, unmedicated and doesn't tear.
While it was difficult to find just a decade back, there is a current surge of bodywork training for pregnancy, birth and postpartum, increasing the chances that you can find a practitioner in your area.
Dr. Elliot Berlin is an award winning prenatal chiropractor, childbirth educator and labor doula. His Informed Pregnancy® Project utilizes multiple forms of media including a podcast, documentary films, blog and youtube series to compile and deliver unbiased information about pregnancy and childbirth to empower new and expectant parents to make informed choices regarding their pregnancy and parenting journey. He and his wife, perinatal psychologist Dr. Alyssa Berlin, live and practice together at Berlin Wellness Group in Los Angeles.