Female rats were exposed to weightlessness in the mid-deck of US "Space Shuttle" in the period between days 9 to 20 of pregnancy and examined on Earth post flight. No significant structural anomalies threatening the life and normal development were found in newborn rats carried by mothers under the conditions of weightless exposures. Water, Na, K, Ca, Fe and Cu contents in fetal and placental tissues of the flight animals were not changed. Differences between the flight and ground-based synchronous controls, or the rates of formation of the fetal skeleton were not revealed. Comparison of these data with results of the experiment aboard biosatellite "Cosmos 1514" in which female rats stayed in weightlessness from day 13 to 18 of pregnancy indicates that the two-fold increase of space flight duration did not add changes in the state of fetuses.