Epidemiology of third and fourth degree tears

Question 1

Incidence of OASIS

Answer 1

5.9% (tripled over last 3 years)
6.9% primips
1.7% multips
Overall incidence 2.9%

Question 2

Lining of the anal canal

Answer 2

The proximal anal canal is lined with rectal mucosa (columnar epithelium) whereas the distal 1–1.5 cm of the anal canal is lined with modified squamous epithelium

Question 3

Button hole tear

Answer 3

Rectal mucosa tear with intact sphincter complex

Question 4

Risk factors for OASIS

Answer 4

• Asian
• birth weight > 4 Kg
• OP
• prolonged second stage
• Instrumental delivery

Question 5

Protective factors

Answer 5

• Episiotomy in instrumental deliveries
• Mediolateral, 60 degrees
• Perineal support when head crowning
• Warm compression during second stage

Question 6

Episiotomy facts

Answer 6

• Needs to be 45-60 degrees
• A 40 degree episiotomy results in a 22 degree angle post delivery
• A 60 degree episiotomy results in a 45 degree angle post delivery

Question 7

Ritgen manoeuvre

Answer 7

Delivering the fetal head, using one hand to pull the fetal chin from between the maternal
anus and the coccyx and the other on the fetal occiput to control speed of delivery