I just found this quote in a mainstream pregnancy book under the section medication and anesthesia.
"the mother anticipating a multiple birth should avoid medication and anesthesia whenever possible. Unless she has been well nourished, her babies may be small or premature and they will have less resistance to the dosages of medication and anesthesia, which will be calculated for the mother's body size. All drugs pass through the sieve-like placentas.... A thorough consideration of this subject can be found in Drugs in Labor and Birth by Doris Haire, who points out that the package insert for the anesthetic marcaine (used for epidurals) contains five pages of adverse effects."1
The catch? The book was last copyrighted in 1991. Somewhere between 1991 and 2007 we seemed to have lost the ability to be very clear about the fact that a birth without medication and anesthesia is not best for mom and baby. Even more interesting is the fact that this book is for moms having twins! It is now standard procedure in many hospitals to place an epidural in a mom expecting twins, just in case.
1 Elizabeth Noble, Having Twins (Boston: Houghton Mifflin Company, 1991) 199.