Foetus lies with its head down against stretched cervix

Weak contraction of uterus every ?30min.

These increase in strength and frequency

Caused by hormone oxytoccin secreted by posterior pituitary gland

When cervix is fully dilated

Expulsion of baby by contractions of mother's abdominal muscles

- Umbilical cord shuts down, isolating baby from mother

- CO₂ content of the blood rises to stimulate baby's first breath

Expulsion of placenta ? ?30min after birth

- Pregnancy lasts ?38 weeks from implantation, 40 weeks from last period