The Problem With Using Animals to Study Pregnancy
In a 2003 article in the European Journal of Obstetrics & Gynecology and Reproductive Biology, Dr. Hobe Schröder states that “in reproductive sciences species differences are especially pronounced.” He continues, “These problems are not unheard of in other whole-animal experiments, but they are especially concentrated and cumbersome in the study of fetal growth.” Schröder goes on to explain that difficulties occur because the study of pregnancy involves complex interactions between the mother’s body, the placenta, and the fetus.1
Sweeping claims about the comparability of animal development and human development are made by animal researchers, but pediatric surgeons Sylvie Beaudoin, Patrick Barbet, and Frédéric Bargy debunk those claims: “The medical literature lacks in accurate descriptions of developmental stages in currently used species. … Moreover, the available descriptions of mammalian embryos are not linked to human development.” It is more than a bit doubtful that experiments on pregnant animals are valid or provide any benefit to human health. Beaudoin et al. question how it can be that “relatively little is known of rabbit development, in spite of the fact that many studies have been carried out on this model.”2
Allen Enders and Anthony Carter, experts in cell biology and human anatomy at the University of California at Davis, reviewed the differences in placental structure across species and warn, “The diversity of placental structures in Eutherian mammals is such that drawing generalizations from the definitive forms is problematic.” They also comment that “we are faced with a nearly overwhelming diversity of methods of implantation of the blastocyst and structure of the placenta.” Enders and Carter are forced to conclude their review by stating, “Study of comparative placentation is a humbling experience.”3
Mice, Rats, Sheep, and More
The most commonly used animals in pregnancy research are rats and mice. Rodents are also used to test the potential toxicity of substances used by pregnant women, which provides unreliable results but is required by current federal law. But in regard to trying to determine cancer risks to developing human fetuses by using animal tests, Lucy Anderson of the National Cancer Institute writes: “[S]tudies with adult rodents, for purposes of human risk assessment, have numerous well-known limitations: large species differences in size, physiology, etc.; absolute exposure times that are much shorter than for humans; necessary use of doses that are often orders of magnitude higher than those encountered by humans; and the practical need, with animals, to study chemicals individually and under uniform standardized conditions, as opposed to the exposure of humans to mixtures, under many different conditions ….”
Anderson goes on to state: “Humans and rodents have different types of placenta, so that the processes of carcinogen penetration and processing (activation, detoxification) by the human placenta may not be closely modeled in the rodent. Mice and humans differ markedly with regard to the physiology of gestation, including roles of the corpus luteum, specific estrogens produced, and estrogen blood levels in mother and fetus …. Human fetal development is much longer than that of the rodent, and some of the organs and tissues of the human newborn are more mature.”4 Despite the fact that many scientists and researchers acknowledge the vast differences between human pregnancies and rodent pregnancies—and therefore choose to study humans directly—there are still those who waste funding and time on useless animal experiments year after year.
The problems associated with the differences between animals and humans are hardly limited to the use of rodents. Sheep are considered the “premier” species for use in reproductive studies, but Michael E. Symonds et al. of the University of Nottingham Medical Centre School of Human Development write, “[B]ecause of differences in placentation between sheep and humans … findings can not be extrapolated directly between species.”5 In fact, pharmacologists Päivi Myllynen and Kirsi Vähäkangas state across the board that “the placental structure shows great interspecies variation … making it unwise to extrapolate placental transfer data from animal studies to humans ….” The pair are forced to conclude that “animal studies give deficient prediction of human placental transfer.”6
Animal Studies Mislead Research >>
1. Hobe J. Schröder, “Models of Fetal Growth Restriction,” European Journal of Obstetric & Gynecology and Reproductive Biology 110 (2003): S29-S39.
2. S. Beaudoin et al., “Development Stages in the Rabbit Embryo: Guidelines to Choose an Appropriate Experimental Model,” Fetal Diagnosis and Therapy 18 (2003): 422-27.
3. A.C. Enders and A.M. Carter, “What Can Comparative Studies of Placental Structure Tell Us?—A Review,” Placenta 25, “Trophoblast Research Supplement,” 18 (2004): S3-S9.
4. Lucy M. Anderson, “Predictive Values of Traditional Animal Bioassay Studies for Human Perinatal Carcinogenesis Risk Determination,” Toxicology and Applied Pharmacology 199 (2004): 162-74.
5. Michael E. Symonds et al., “Current Topic: Limitations of Models Used to Examine the Influence of Nutrition During Pregnancy and Adult Disease,” Arch Dis Child 83 (2000): 215-19.
6. P. Myllynen and K. Vahakangas, “An Examination of Whether Human Placental Perfusion Allows Accurate Prediction of Placental Drug Transport: Studies With Diazepam,” Journal of Pharmacological and Toxicological Methods 48 (2002): 131-38.
