Birth Chapter 19

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

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.

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).

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.

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

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

Newborn – the neonate Anthea Sieveking, Wellcome Images

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

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

Youtube clip Labour National Geographic https://www.youtube.com/watch?v=YlISC6KsY cc