I remember being almost five months pregnant with my first child and my obstetrician saying he was certain I'd have a C-section. He "could just tell" that my body wasn't equipped to deliver the baby I was carrying and I would inevitably need surgery. One trimester later? A stalled induction and an emergency C-section. While I was suspicious of his reasoning, I justified what happened with the knowledge that I was just a naive first-time mom who should just trust that my medical provider knew more than I did. But really, does hip size affect childbirth? Can a doctor really look at your body and determine if a baby's going to pass through?
"You can’t look at a woman’s hips and see if she’s going to be good at childbirth," says midwife Rachel Hart, who runs Birthing Way Homebirth Midwifery Care in Marietta, Georgia. "And we're not really talking about hips, we're talking about the entire pelvis. If childbirth is going to be affected structurally, it’s because of the shape of the pelvis and the position of the baby."
And it turns out, a trial of labor is the only way to determine whether those factors line up properly for a successful birth, Hart tells Romper. The good news, however, is that it's extremely rare for it not to. "That is really rare, so when people say the baby was too big, always be suspicious of that because it’s really rare that a woman grows a baby she cannot give birth to."
There are, however, more optimal shapes to the pelvis that allow babies to change position and move easily out of the birth canal. A gynecoid pelvis is the ideal shape for childbirth, Hart says, because of its bowl-like appearance from above and round inlet that allows infants to escape the pelvis with little interference from their mother's bone structure. Other shapes include android, anthropoid, and platypelloid that either have more narrow inlet openings or less room front-to-back for the baby to get into position.
"When you’re looking down into the pelvis, gynecoid is like a bowl," Hart says. "The others, [they're] more narrow and eliminate space for the baby to move through, but for the most part it can still happen."
But what does it look like when pelvis shape does come into play? Labor would stall out and a C-section would become necessary. "It would be an arrest of labor where the baby would stop descending after hours and hours, and they get so far down and keep pushing and the baby absolutely cannot go any further," Hart says. "And that is really rare."
One very weird finding reported by Mental Floss is that women's hips may change shape over the course of their lives to accommodate childbearing, but it's front-to-back width that increases during their fertile years to increase the size of the birth canal. Using CT scans of pelvic bones from 275 male and female subjects, researchers found that boys' and girls' pelvises have the same shape until puberty. Boys' bones increased in size but remained the same proportionally, while the girl's bones expanded to accommodate a baby's passage through the birth canal. The weird thing, however, was that women's bones seemed to narrow to a more "efficient shape" once their most fertile years are behind them, the article reported.
Besides stalling out in labor, is there anything moms-to-be can do to prevent a collision between her baby and her bones in childbirth? According to Hart, "There are things they should focus on that can create a positive outcome, namely nutrition and exercise. They should focus on that rather than whether they have a good pelvis."
By having a healthy, strong body that's ready for labor, you and your baby should be able to manage whatever difficulties arise, regardless of your pelvis size or hip shape.