Animation showing a human embryo at week 10 (8 weeks after conception). The human gestation period is typically around 40 weeks after the last period, or 38 weeks after fertilisation (conception). For the first eight weeks from conception the developing baby is known as an embryo, and as a foetus for the subsequent 30 weeks. The developing baby is nourished through its umbilical cord, which connects to an organ called the placenta, which is embedded in the wall of the mother's uterus.