Thyroxin and progesterone concentrations in pregnant, nonpregnant bitches, and bitches during abortion

Serum progesterone and thyroxin concentrations were measured weekly until 61 to 62 days after ovulation in 24 pregnant bitches and in the control group of nine nonpregnant bitches in the luteal phase. Fourteen of the 24 dogs had a normal pregnancy and parturition. Ten of the 24 dogs showed mucinous or colored vaginal discharge, decreased appetite, or lethargy. These initial signs of abortion or fetal resorption were noted during the fourth week of pregnancy, and the process occurred over the next 2 weeks. Progesterone and thyroxin concentrations were measured by quantitative ELISAs validated to dog serum. The serum progesterone concentrations of the group going through abortions differed significantly from the third week until the end of the eighth week. The mean serum thyroxin concentrations of healthy pregnant and nonpregnant groups significantly exceeded the reference range (20-45 nmol/L). The serum thyroxin concentrations in the abortion group were between 16.15 ± 3.17 and 40.78 ± 8.97 nmol/L. The values in this group were significantly different from the other two groups at the third week of the luteal phase. Clinical signs of abortion or fetus resorption manifested in midpregnancy. The clinical signs of abortion coincided in each case with a low serum progesterone concentration (<10 ng/mL). This phenomenon indicated, in contrast with other studies, that the decrease of serum progesterone below 10 ng/mL at the fourth week of pregnancy may signal impending abortion. In the second half of pregnancy, the thyroid gland was not able to respond adequately to the elevated requirement in thyroid hormone, although in other periods of the ovarian cycle, there were no clinical signs of hypothyroidism.