THE per cent of premature births is higher in strain 13 guinea pigs than in any other strains or stocks for which data are available (13, 23, 58). Analysis of the records at Kansas revealed that this high per cent of wastage occurred during the second half of pregnancy. The first loss was on day 35 but most was in the third trimester which begins day 47. This wastage toward the end of pregnancy in strain 13 females suggested that a study of these animals might lead to identification of a factor exerting its effect late in gestation. When the results from a preliminary study (27) revealed that the thyroid is involved, the desirability of looking into related problems became apparent. At what time in gestation, does the thyroid hormone become important for such an action? What are the effects of a more severe hypothyroidism than was produced in an earlier study of the thyroid and gestation (46)? How are the effects of the hypothyroid state on reproduction, such as the low per cent of vaginal openings and the low incidence of heat responses (46) to be explained?
No takes yet. Share an insight, caveat, or question.
Hoar et al. (1957) studied this question.