I'm wondering whether the theory/rumor (which I'd first heard about 7 yrs ago) that moms who were in pain because they'd refused pain-relief drugs while in labor actually CAUSED pain for their infants. I'd hitherto dismissed this as just another specious argument that OBs like to come up with (though they might actually believe it themselves) to scare moms into compliance with their agenda, but I would like to know whether anyone actually did any study on the subject and, if so, whether it had any scientific merit.
More specifically, the theory is that the stress hormones produced in response to the mother's pain harm the baby. To begin with, contractions themselves are not painful for the baby, although they generally are for women. Babies experience contractions as an all-over stimulating massage. Contractions are painful for the mother because the cervix is stretching, but the baby is being squeezed, which is quite a different thing. To see this, pull gently at the corners of your mouth, and you will see that it doesn't take much stretch to sting. Now grab your forearm and squeeze and release, and, if anything, it feels good.
Returning to the stress hormones (catecholamines) produced in response to labor pain, normal levels benefit both mom and baby. They give mom the energy and stamina she needs to accomplish the birth, and they prepare the baby for life in the outside world by drying out the lungs, raising blood sugar levels, and producing the wide-eyed, alert period that mutually engages parents with their newborns after birth. Pain in Labour: Your hormones are your helpers by Dr. Sarah Buckley will give you more information on this. And, yes, we have research that backs this up.
On the other hand, while the normal stress of labor is beneficial, extreme anxiety or fear can be detrimental. However, distress may be caused by preventable outside factors. Penny Simkin explains in a review article that studies in laboring monkeys in which researchers pinched their toes, shined bright lights in their eyes, or jumped up and down in front of their cages did, indeed, show oxygen deprivation in the monkey fetuses. But the baby monkeys did fine--until doctors hurt or frightened their mothers. Penny Simkin writes, "Much of the stress of labor is preventable because many of the stressors . . . are imposed in the form of thoughtless routines, unfamiliar personnel, and technological interventions."
Simkin P. Stress, pain, and catecholamines in labor. Part 1. A review. Birth 1986;13(4):227-33.