Blood transfusions are actually among the least invasive medical procedures performed on fetuses. More intrusive is endoscopic fetal surgery, in which surgeons manipulate a joystick-like instrument while watching the fetus on an ultrasound screen. Most invasive of all is open fetal surgery, in which a pregnant woman’s uterus is cut open and the fetus exposed. Ray Paschall, an anesthesiologist at Vanderbilt Medical Center in Nashville, remembers one of the first times he provided anesthesia to the mother and minimally to the fetus in an open fetal operation, more than 10 years ago. When the surgeon lowered his scalpel to the 25-week-old fetus, Paschall saw the tiny figure recoil in what looked to him like pain. A few months later, he watched another fetus, this one 23 weeks old, flinch at the touch of the instrument. That was enough for Paschall. In consultation with the hospital’s pediatric pain specialist, “I tremendously upped the dose of anesthetic to make sure that wouldn’t happen again,” he says. In the more than 200 operations he has assisted in since then, not a single fetus has drawn back from the knife. “I don’t care how primitive the reaction is, it’s still a human reaction,” Paschall says. “And I don’t believe it’s right. I don’t want them to feel pain.”

But whether pain is being felt is open to question. Mark Rosen was the anesthesiologist at the very first open fetal operation, performed in 1981 at the University of California, San Francisco, Medical Center, and the fetal anesthesia protocols he pioneered are now followed by his peers all over the world. Indeed, Rosen may have done more to prevent fetal pain than anyone else alive  except that he doesn’t believe that fetal pain exists. Research has persuaded him that before a point relatively late in pregnancy, the fetus is unable to perceive pain.

Rosen provides anesthesia for a number of other important reasons, he explains, including rendering the pregnant woman unconscious and preventing her uterus from contracting and setting off dangerous bleeding or early labor. Another purpose of anesthesia is to immobilize the fetus during surgery, and indeed, the drugs Rosen supplies to the pregnant woman do cross the placenta to reach the fetus. Relief of fetal pain, however, is not among his objectives. “I have every reason to want to believe that the fetus feels pain, that I’ve been treating pain all these years,” says Rosen, who is intense and a bit prickly. “But if you look at the evidence, it’s hard to conclude that that’s true.”

Image Credit... Artwork by Brian Dettmer; Photographs by Tom Schierlitz

Rosen’s own hard look at the evidence came a few years ago, when he and a handful of other doctors at U.C.S.F. pulled together more than 2,000 articles from medical journals, weighing the accumulated evidence for and against fetal pain. They published the results in The Journal of the American Medical Association in 2005. “Pain perception probably does not function before the third trimester,” concluded Rosen, the review’s senior author. The capacity to feel pain, he proposed, emerges around 29 to 30 weeks gestational age, or about two and a half months before a full-term baby is born. Before that time, he asserted, the fetus’s higher pain pathways are not yet fully developed and functional.

What about a fetus that draws back at the touch of a scalpel? Rosen says that, at least early on, this movement is a reflex, like a leg that jerks when tapped by a doctor’s rubber mallet. Likewise, the release of stress hormones doesn’t necessarily indicate the experience of pain; stress hormones are also elevated, for example, in the bodies of brain-dead patients during organ harvesting. In order for pain to be felt, he maintains, the pain signal must be able to travel from receptors located all over the body, to the spinal cord, up through the brain’s thalamus and finally into the cerebral cortex. The last leap to the cortex is crucial, because this wrinkly top layer of the brain is believed to be the organ of consciousness, the generator of awareness of ourselves and things not ourselves (like a surgeon’s knife). Before nerve fibers extending from the thalamus have penetrated the cortex  connections that are not made until the beginning of the third trimester  there can be no consciousness and therefore no experience of pain.

Sunny Anand reacted strongly, even angrily, to the article’s conclusions. Rosen and his colleagues have “stuck their hands into a hornet’s nest,” Anand said at the time. “This is going to inflame a lot of scientists who are very, very concerned and are far more knowledgeable in this area than the authors appear to be. This is not the last word  definitely not.” Anand acknowledges that the cerebral cortex is not fully developed in the fetus until late in gestation. What is up and running, he points out, is a structure called the subplate zone, which some scientists believe may be capable of processing pain signals. A kind of holding station for developing nerve cells, which eventually melds into the mature brain, the subplate zone becomes operational at about 17 weeks. The fetus’s undeveloped state, in other words, may not preclude it from feeling pain. In fact, its immature physiology may well make it more sensitive to pain, not less: the body’s mechanisms for inhibiting pain and making it more bearable do not become active until after birth.