Pregnant woman. Side view of the swollen abdomen and breasts of a pregnant woman. Human pregnancy lasts for around 40 weeks. An egg cell (female reproductive cell) is fertilised by a sperm cell (male reproductive cell) and implants in the mother's uterus. The fertilised egg, or zygote, develops through stages called an embryo and a foetus, before it is born as a human baby. The mother's abdomen has swollen to contain the developing foetus, and her breasts are swollen with the milk with which she will feed her baby.