There are 4 common pelvis shapes found in birthing individuals and each pelvis shape affects labor and delivery differently.
The most common pelvis shape is the gynecoid pelvis. This pelvis shape is found in roughly 50% of birthing individuals. The inlet of the pelvis has a nice oval shape. The mid-pelvis area, located between the ischial spines is adequate in size. This means that there is enough room for a baby to pass through without troubles. The sacrum is wide and relatively short. It slopes backwards with a deep curve from the sacral promontory to the coccyx. The sidewalls of the pelvic brim are straight and parallel to each other. The ischial spines are not prominent and the pubic arch is wide and round. You can expect to fit roughly 2 fingers width in the pubic arch of a gynecoid pelvis.
The next most common pelvic shape is called the anthropoid pelvis. This pelvis type is seen in roughly 25% of birthing individuals. The inlet of the pelvis is shaped as a long, anteroposterior oval. The midpelvis is long in diameter. The sacrum is also long as well as being narrow. The sidewalls are straight and the ischial spines are variable. The pubic arch will either be normal in size, similar to the gynecoid pelvis, or it can be relatively narrow.
The third pelvis shape is referred to as the android pelvis. This pelvis shape is found in about 20% of birthing individuals. The inlet of this pelvis type is heart-shaped. The mid-pelvis diameter is reduced in size. The sacrum is typically flat, long, and narrow with a forward incline. The sidewalls are convergent and the ischial spines are prominent. The pubic arch is both narrow and deep.
The last pelvis type is called the platypelloid pelvis. This is by far the least common pelvis type, seen in only 5% of birthing individuals. The inlet is a long, transverse oval shape. The midpelvis is short in diameter. The sacrum is wide, deeply curved, and more often than not sharply angulated with enlarged sacral bones. The sidewalls are parallel and straight. The ischial spines are variable. The pubic arch is usually very wide and flattened. Often, three fingers can fit in between the pubic arch of a platypelloid pelvis.
By performing a pelvimetry exam, providers can have a deeper understanding of how a client's pelvis is shaped and how they can best assist them in a successful vaginal delivery.
Performing a pelvimetry exam is a 6 step process.
The steps are as follows:
Upon donning the proper PPE and receiving the client’s consent, the provider will insert their pointer and middle finger into the vaginal opening, leaving their thumb hooked on the outside of the vulva. The provider will reach back as far as possible in attempts to touch the sacral promontory. In some pelvis types this will not be possible, in which case the provider will note that the distance from the pubic symphysis to the sacral promontory exceeds the reach of their hand. This maneuver is performed to measure the size of the pelvic inlet.
The provider will then rotate their hand to where their fingers are lying flat against the sacrum. Upon locating the sacrum, the provider will run their fingers down the sacrum to the coccyx to assess sacrum width, angle, and curvature.
The provider will then run their fingers back up the sacrum and along the sidewalls of the pelvis to assess if they are straight and/or parallel.
Following the curve of the sidewalls, the provider will work their way down to the ischial spines to assess the prominence of the spines as well as the diameter of the midpelvis.
They will then continue to follow along the pelvis towards the pubic arch. This is where they will assess the width and curvature of the pubic arch.
The final step is performed externally. The provider will remove their hand from the vagina and will create a closed fist. They will place their closed fist against the base of the vagina and will measure the width between the ‘sits bones’, otherwise referred to as the pelvic outlet.
These steps will give the provider a clear understanding of their clients pelvis and a possible prediction of any complications that could arise during labor and delivery due to the size and shape of their pelvis.