Flaws in the Design of O’Hagan’s Experiment
This brief list offers only the most basic reasons why pregnant rabbits can’t teach us about pregnant women. Included are the physiological differences between women and rabbits that make extrapolation impossible and the facts that invalidate a study on blood flow and pregnancy. Any one of these disparities would cast doubt on the validity of an experiment. Together, they spell out the absurdity of studying human pregnancy by putting rabbits on treadmills:
- Human gestation lasts for nine months, whereas rabbit gestation lasts for only one month.
- Humans typically have one baby at a time, whereas rabbits carry litters of many bunnies. (Humans are designed for a qualitative reproduction strategy, bearing a single offspring only occasionally, whereas rabbits are designed for quantitative reproduction, or the constant bearing of large numbers of offspring.)
- The human fetus attaches to the uterine wall through a different kind of placenta than rabbit fetuses, making for different blood flow and nutrient transfer (for example, the apposition of the fetus to the uterine wall is villous in humans and labyrinthine in rabbits).
- Humans walk upright and rabbits walk on all fours. This difference in posture affects the forces acting on blood flow; the spatial relationship between the fetus and key organs, such as the heart; and how the fetus moves during physical activity.
- Large mammals, like humans, dispel heat far less efficiently than small animals, like rabbits, because small animals have a proportionately greater surface area. This leads to an array of differing physiological characteristics; for instance, humans sweat to release body heat and rabbits don’t. Rabbits insulate with fur, dispel heat through their large ears, and burn more calories through activity, and their hearts must beat much faster.
- On average, the human heart beats 60 to 80 times in one minute, whereas rabbits’ hearts beat, on average, more than 200 times each minute—that’s three times faster.
- O’Hagan’s confined rabbits receive deficient levels of exercise between their exercise trials. They are locked in the university’s animal facility and are not allowed free movement, which is the equivalent of strapping a woman to a bed for her nine-month pregnancy, letting her up only a handful of times to run on a treadmill.
- Treadmills are designed to simulate walking. The steady rotation of a conveyor belt fits poorly with the way rabbits hop, making the exercise trials unnatural.
O’Hagan justifies her study by claiming that it will help battle preeclampsia, but the NHLBI Working Groups on Research on Hypertension During Pregnancy states, “Animal models are of limited benefit because of significant differences in placentation among mammals, as well as differences in length of gestation and perhaps even posture between mammalian models and humans.”
