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Prediction of OASIS

Risk factors for OASIS have been assessed and results are inconclusive, hence, identifying
risk factors may not allow the accurate prediction of the injuries. However, obstetricians and

midwives need to be aware of risk factors for OASIS in order to reduce the occurrence or minimize

the severity of possible perineal tears. The following maternal and obstetrical risk factors have
been identified based on recent systematic reviews. (9, 10)

• Maternal risk factors
OASIS were more frequent in the following types of women:

- Nulliparous women with adjusted Odds Ratio (ORa) of 4.19 (95%CI 3.03-5.84);

- Women with a history of previous caesarean section, with ORa 5.59 (95%CI 3.68-8.44);
- Gestational or pre-pregnancy diabetes, with ORa 1.76 (95%CI 1.22-2.46)

- Women in whom the uterine fundal height was greater than 32 cm, with ORa 1.35

(95%CI 1.03-1.77).

• Obstetrical risk factors

Obstetrical risk factors for OASIS are:
- Heavier infants, mean difference 192.88 g (95% CI, 139.80-245.96 g);

- An episiotomy, OR 3.82 (95% CI, 1.96-7.42);

- Vaginal assisted delivery, ORa = 1.81 (95%CI 1.18-2.86);
- An operative vaginal delivery, OR 5.10 (95% CI, 3.33-7.83);

- The use of a second instrument or an obstetrical manoeuvre, ORa = 1.93 (95%CI 1.05-

3.30);

- Epidural anesthesia, OR 1.95 (95% CI, 1.63-2.32);

- Labor induction, OR 1.08 (95% CI, 1.02-1.14); and
- Labor augmentation, OR 1.95 (95% CI, 1.56-2.44).

Prevention of OASIS (11, 12)

Although there is need for more research on preventative strategies for OASIS, some

interventions have evidently demonstrated their efficacy in reducing the incidence of OASIS. On
the contrary, some routine practices do not have strong evidence to support.

Obstetric Anal Sphincter InjurieS (OASIS): Impact and prevention 71