Comparison of pregnancy in rodents and humans

Many of the features of pregnancy in rodents are different than in humans, such as a gestation length of 3 weeks versus 9 months and the fact that rodents usually give birth to litters rather than singletons. Despite these obvious differences, however, the fact that rodents can develop pre-eclampsia shows that there is more in common between rodents and humans than is widely appreciated. A number of anatomical and physiological features of pregnancy are similar in humans and rodents (Table 14.1). At a structural level, the conceptus in rodents, as in humans, invades into the uterine wall after implantation and promotes increased maternal blood flow to the implantation site by promoting both increased blood vessel formation (angiogenesis) and vasodilation (Cross et al., 2002). The outermost cells of the rodent placenta (trophoblast giant cells) are analogous to extravillous cytotrophoblast cells in humans invade

Table 14.1. Comparison of pregnancy and placental structure in humans and mice

Human

Mouse

Length of gestation

9 months

20 days

Stage of implantation

7 days

4.5 days

(post-fertilization)

Initiation of fetal

21 days

8.5 days

heartbeat

Vascularization of

25 days

10 days

placental villi

Hemochorial blood

Yes

Yes

flow through

placenta

Chorionic villi lined by

Yes

Yes

syncytiotrophoblast

Invasive trophoblast

Extravillous

Trophoblast

cell subtype

cytotrophoblast

giant cells

entering uterine

spiral arteries

into the spiral arteries and replace their endothelial linings, promoting the transition from endothelial lined artery to trophoblast-lined (hemochorial) blood space. The bulk of the mature placenta is a villous tree-like structure, called the labyrinth, that forms the surface for nutrient and gas exchange (Cross, 2000; Cross et al., 2003; Rossant and Cross, 2001). The labyrinth is covered by three trophoblast layers (two layers of syncytiotro-phoblast), and has an inner core with a dense capillary network. At a physiological level, rodents and humans show a similar fall in blood pressure during late gestation that is likely initiated by feto-placental factors (Davisson et al., 2002; Wong et al., 2002).

Studying development and the physiology of pregnancy in rodents obviously has considerable advantages because of the ability to carefully control both genetic and environmental influences. Indeed, in mice, it is possible to alter gene function using transgenic and knockout mouse approaches, and by control of the way in which mice are bred or embryo transfer between normal (wildtype) and mutant strains it is possible to control whether the altered gene is present in the feto-placental unit, the mother or both. In addition, because gestation is short and the reproductive tract is relatively small in rodents, it is possible to analyze the events of pregnancy in great detail.

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Responses

  • eric
    How similar are mice to humans pregnancy?
    2 years ago

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