Gestation period of 272 pregnancies, where mating was observed, ranged from 143 to 159 days. 90% of all pregnancies lasted between 147 and 155 days.

Gestation period decreased with increasing litter size. On average it was 152.0 days for singles, 150.9 days fro twins, 149.5 days for triplets, and 146.8 days for quadruplets.