1. Birth
Chapter 19

2. Keywords Birth Partuition Stages of labour Dilation Breaking of waters
Expulsion
Placental delivery
Changes in foetal circulation
Bypassing the liver
Ductus venosus
Bypassing the lungs
Ductus arteriolus
Connecting atria
Foramen ovale

3. Giving birth - parturition
Childbirth, or labour, is preceded by a rise in the levels of estrogen and oxytocin in the mothers bloodstream.
Labour begins with contractions of the muscular walls of the uterus. These contractions start at the top of the uterus and sweep down to the cervix.
As labour progresses contractions become stronger and more frequent.

4. Three stages of labour Labour is often divided into three stages
1. Dilation
Contractions force the baby’s head into the cervix, stretching it until the head enters the birth canal (the vagina).
At this stage the ‘waters’ usually ‘break’ (i.e. the amnion bursts and releases the amniotic fluid).

5. Three stages of labour 2. Expulsion
The baby moves into a face-down position
Contractions become stronger and closer together, forcing the baby through the birth canal.
3. The placental stage
A final contraction of the uterus expels the placenta, umbilical cord and membranes (the after-birth) from the mother’s body.

6. Baby in delivery position
Medical Art Service, Munich – Wellcome Images

7. Delivery A B C Stage 1a – early dilation Stage 1b – late dilation
Stage 2 - expulsion C

8. Newborn – the neonate
Anthea Sieveking, Wellcome Images

9. Changes in foetal circulation
Before birth
Blood supply is connected to the umbilical cord and placenta
Gas exchange and nutrient acquisition happens in the placenta
Heart has a connection between the left and right atria
Foramen ovale
Main blood supply bypasses the lungs
Ductus arteriosis
Main blood supply bypasses the liver
Ductus venosus

10. Changes in foetal circulation
After birth
The alveoli in the lungs expand and fill with air
This change increases the blood supply to the lungs and liver
After a few weeks the ductus arteriolus and ductus venosus have shriveled and disappeared
The pressure in the atria increases, and closes the foramen ovale in the heart

11. Youtube clip Labour National Geographiccc