On the night of January 18, 1991, during the Gulf War, Scud missiles launched by Iraqi troops began exploding in Israeli communities. Citizens were alerted by howling air-raid sirens that blared from outdoor speakers and on the radio and TV. Since there was a terrifying possibility that the bombs were carrying chemical payloads in addition to their explosive power, the frightened populations had been instructed to don gas masks and seek shelter when they heard the wail of a siren.
In the maternity ward of a Tel Aviv-area hospital that night, three women were in labor. As is standard practice, they had been fitted with fetal heart monitors that strapped around their bellies to keep track of their babies’ heartbeats. At three a.m., a sudden, terrifying shriek of a Scud alert siren penetrated the walls of the maternity ward—and, apparently, the wombs of the expectant mothers. As hospital staff scrambled to put gas masks on themselves and their patients, the nurses noticed something highly unusual on the fetal monitors. The heart rates of all three of the about-to-be-born infants suddenly and unexpectedly.… plummeted. From a healthy and brisk 100 to 120 beats per minute they slowed by half, to a frightening 40 to 60. The tiny hearts “lay low” like this for two minutes and then returned to normal.
All three babies, who hadn’t yet even heard their parents’ voices outside the womb, responded physiologically, with bradycardia, to the sound of danger. Some of the slowing may have resulted from the sounds of the siren itself and some from maternal stress hormones entering the fetus’s body in response to the siren. Either way, these obstetrical observations strongly suggest that even prior to birth itself, we’re equipped with unconscious anti-predator defenses, including a potent alarm bradycardia response. All three babies were ultimately born healthy, as well as apparently armed with the full complement of survival instincts we all possess but rarely think about.