12/01/2025
The average newborn head (think 50th percentile) is approximately 11 cm across. Not 10 cm.
And for those with bigger than average babies? Those heads can be 12-13 cm across.
Wondering what the heck is going on? High school algebra - let’s go! ⤵️
To find the diameter:
d = C/pi
Average newborn head circumference (C)? About 13.5 inches, which equals approximately 34.3 cm.
So… d=34.3/3.14 ➡️ That average head is approximately 11 cm across - 1 cm MORE than complete dilation. Excuse me, but what?!
Real answer?
10 cm dilation - and wanting to push - is really related to the presenting part of the baby. Most of the time, when that head hits the outlet of a fully dilated cervix, it’s about 10 cm across. When babies are OP (sunnyside up), face, or brow presenting, this can make that presenting part wider (and thus harder) to push out and through. Can it still be done? Yes of course! But this is part of why it may be tougher or take longer.
The other thing we’ve got going for us is the movable bones of the baby’s skull - yep, that is totally needed to fit those heads through this space. And lastly? Our tissues continue to stretch and give space AFTER 10 cm has been reached and the cervix has reached 10 cm.
Big takeaway? Many baby have a head BIGGER than 10 cm across. And, because of the craziness of your body (and their little baby heads), they can still fit. And also? Somebody give you a push present. 🎁
You don’t have to know your algebra, but you do need to know how to help these babies fit and all the things you two can do and try and I can help you with that! My birth course is on 52% off sale until tonight! Comment BF25 and I’ll send you the details.
It is freakin crazy but it also works so good when you show up ready.
So how big was your baby’s head? Mine always had smaller than average heads, thank you!