During the birth process, the baby passes through the pelvis. Many, many people worry about that whole process during their pregnancy. The good news is that the vast majority of the time, the shape of the pelvis, combined with the body’s ability to shift the pelvic opening during the birth process and the baby’s ability to mold it’s head means that everything goes very smoothly.
Some care providers try to assess the shape of the pelvis at an early prenatal visit, by feeling the pelvic outlet (the opening at the bottom of the pelvis) during a vaginal exam. Unfortunately, there has been little research done on this kind of pelvimetry by hand since the days of twilight sleep, so whether or not it is at all accurate, especially since obstetric care has changed so much since then, is highly debateable.
When they do this, they are looking at the shape in between the bones to get an idea of whether or not the baby will fit. Here’s an example of what kinds of shape differences they might look for:
These two shapes are the most common variants. Often the one on the left is described as an “android pelvis” or “male pelvis”, while the one on the right is described as a “gynecoid pelvis” or “female pelvis”. The truth is, for most people, the pelvis is somewhere in between these two rather than strictly one or the other. Any variation in this spectrum is normal and can work for birth.
There are other possible pelvic shapes that are more rare that can impact the birth process to varying degrees. If your care provider tells you that you have one of these unusual pelvis shapes, take the time to ask all the questions you have, and consider a second opinion if you feel the need for that.
Keep in mind that pelvic shape is only ONE factor in the ability to birth. The pelvis can shift and change to accommodate the baby passing through (and staying upright and mobile during birth can help with that.) The baby’s head can mold as the baby’s skull adapts to fit through the pelvis as well.
With lots of patience and a skilled care provider, it’s possible to give birth with the vast majority of pelvis shapes!