Simple question: Does head size of child coincide with the mother’s vagina size? Say, does a big headed kid have a mom with a big ol’ thang, and a kid with a skinny little head… Well, hell, you get the point.
–Tim
Nope. Muscle will usually stretch to accomodate.
There might be an argument for a correlation with pelvic bone size though I’d guess it would be poor. You also need to factor in there can be a couple of weeks difference in the gestation period which makes a huge difference to birth dimensions. After birth genetics and nutrition take over.
All three of the woolly lambs were on the 95th percentile at birth but are now heading toward the 30-40th percentile of mark of their parents. All were caesarians.
We did a survey in our office at one stage. Of 25 people, the only one who weighed more than 8lbs at birth was the weediest guy in the office. He weighed in at almost 11lb and doesn’t look like he weighs much more 30 years later 
The size of the baby depends on lots of stuff, but not vaginal size. Genetics plays a big role. Diabetics mothers with poor sugar control give too much or too little glucose to their babies… hence they tend to be large, or small. Malnourished babies tend to make the best of things and since the brain gets preferential treatment, the head will be larger than the body. Their are five diffeent shapes of pelvises of varying shape, some of which make birthing more difficult. Ultrasounds are done during pregnancy, and the symphysis-fundus heights are measured routinely… big babies go to Caesarean, or episiotomies (forceps/vacuum) are used if necessary… that is a cut is made to widen the opening and stiched up later. That said, the babies head is surprisingly elastic. If you apply a 25 cmHg vacuum, you get a bump on the babies head the size of a Dixie cup (a small 100mL paper cup sometimes seen by water coolers) which disappears after a day or so.
Just adding to Dr Paprika’s post.
The baby’s head is elastic because the skull is incomplete. In a neonate, there are two large openings under the scalp where bone does not exist yet: the fontanelles. They do not close completely over until the baby is into its second year of life.
The fontanelles are vital for delivery, because the skull can deform to allow passage through the maternal pelvic ring. Once past that, the rest of the birth canal, being muscular, can dilate as necessary to facillitate delivery.
Mom who has given birth to two Big Headed Kids stepping in here…
The preggo hormones soften everything up. The vagina, having no hard parts, is already quite elastic and gets more so as the birth approaches; by the end of pregnancy, the hormones have managed to make even the joints of the pelvis slightly elastic. So there’s a surprising amount of room for the baby’s head, unless the mother-to-be happens to have an unusually small pelvis. Tears in the perineum (the soft tissue between the vagina and the anus) are a more likely complication than a stuck baby.
Both of my boys were born vaginally, with no particular assistance. How likely you are to have a c-section or other medical intervention seems to depend on where you live and what your medical care professional’s attitude is towards intervention.
If what you’re trying not to ask, Homer, is whether a woman who had a big headed kid will be as “tight” as a woman who had a little peanut skull, well, no woman who has had a vaginal birth ever goes completely back to the same size. But I’ve never heard any evidence that the size of the kid makes a difference a year or three down the road.
That may be the case with vacuum assistance, but my brother in law Danny has an elongated skull. He was delivered with the assistance ofForceps. I’ve heard the term “forceps babies” before. His head has always BEEN bullet-shaped, and at the age of 45, won’t be shifting to a more comely spheroid shape any time soon. His mother blames the forceps.
And, for your further edification, This is a site that gives a guide to Litigation over Forceps and Vacuum deliveries. Hmmm…
Cartooniverse
Thanks for the info, guys. To clarify a bit, though, I meant specifically head size in relation to body size, not overall birth weight.
I have also noticed that the larger babies tend to be skinnier as adults, and the smaller babies tend to be larger as adults. Is this studied or proven or anything? Perhaps a leftover prenatal craving for additional nutrition or something?
–Tim
Mothers always blame the forceps, occasionally with good reason. It should be noted, though, that forceps are generally used for difficult labours with a prolonged second stage (i.e. dilation from 3 to 10cm with slow dilation after oxytocin augmentation, etc.). Birthing itself can be very hard on babies and their head shape if forceps are NOT used since the babies head moulds to fit the pelvic outlet size with varying success depending on its presentation (the baby’s head diameter can be as low as 8.5 or as high as 13.5 cm, roughly). Lots of babies are born withoput forceps that have turricephaly, brachycephaly or other deviations in head shape, which last for days or last for life. Contrary to popular belief, forceps are not “tongs” but are shaped like a shallow “S” and cannot “squeeze” the babies head because the curved parts come into contact and prevent this. That being said, forceps need to be applied by trained personnel and it is difficult to use then to section or apply a vacuum. I don’t know the circumstances of the birth you describe… in the past, forceps were probably used much more often than today at most centres. The obstetricians here in Spittleville use them quite often compared to bigger centres, I’ve never seen, only read about, the problems you describe.
I was a forceps birth, and there was no distortion to my skull. (My state of mind inside could be another matter - :)).
According to my mother, the only thing she was concerned about was whether I’d have scars or not (had none) because she’d head Frank Sinatra was a forceps birth and had scars behind his ears for life. Dunno how true that was, though …