Restraint-induced maternal stress and alteration of ossification in mouse fetuses.

Jcl:ICR pregnant mice were immobilized for 120 minutes from days 8-12 of gestation, and their fetuses were examined for skeletal features on day 18 of gestation. In the stressed group, decreased maternal bodyweight gain and lower fetal weight were noted. In this group, the incidences of segmentation defects, fused ribs, absent lumbar vertebrae and full supernumerary ribs were increased in fetuses. In addition, fusion of the basi- and ex-occipital bones was frequently observed in this group (12.9%). This finding was seen at an incidence of 1.4% in the control group, usually in newborns during the ossification process of the occipital bone. Therefore, the fused basi- and ex-occipital bones were considered to be due to altered ossification, but not to be an abnormality. In summary, immobilization of Jcl:ICR mice during the period of fetal organogenesis induced altered ossification of the occipital bones as well as some abnormalities and supernumerary ribs.