Sheep are pregnant from 142 to 152 days with the average gestation period being 147 days. Breed differences have an effect on the length of gestation, making it somewhat shorter or longer than the average. For instance, Finnsheep have shorter pregnancies than Rambouillet sheep.
Female sheep, called ewes, carrying more than one lamb at a time have shorter pregnancies than the average. Gestation periods are longer for ewes carrying male or heavy weight lambs, while female lambs result in shorter pregnancies. The first 30 days of gestation are the most critical, as this is when implantation takes place and most embryonic miscarriages occur.