What is the rate of third (3rd) and fourth (4th) degree perineal lacerations with assisted vaginal birth, specifically with the use of forceps or vacuum extraction?

From the Guidelines

The rate of 3rd and 4th degree perineal lacerations with assisted vaginal birth is approximately 3.3% and 1.1%, respectively, as reported in a recent study published in the American Journal of Obstetrics and Gynecology 1.

Key Findings

• The prevalence rates of perineal lacerations vary, with third-degree lacerations ranging from 1.8% to 7.1% and fourth-degree lacerations ranging from 0% to 0.3% 1.
• Assisted vaginal birth, including forceps-assisted and vacuum-assisted deliveries, carries a higher risk of severe lacerations compared to spontaneous vaginal deliveries.
• Risk factors that increase the likelihood of 3rd and 4th degree perineal lacerations include primiparity, midline episiotomy, persistent occiput posterior position, larger infant birth weight, and shorter perineal body length.

Recommendations

• Healthcare providers should consider selective rather than routine episiotomy to reduce the risk of severe lacerations.
• Appropriate instrument selection based on clinical circumstances, proper technique with gradual delivery of the fetal head, and adequate perineal support during delivery can also help minimize the risk of 3rd and 4th degree perineal lacerations.
• The repair of third- and fourth-degree lacerations should sequentially proceed from deep to superficial structures, including the anorectal mucosa, anal sphincter complex, rectovaginal fascia, perineal body, perineal skin, and vaginal muscularis and epithelium 1.

From the Research

Rate of 3rd and 4th Degree Perineal Lacerations with Assisted Vaginal Birth

• The rate of 3rd and 4th degree perineal lacerations with assisted vaginal birth is a significant concern, as it can lead to severe morbidity and long-term complications 2, 3.
• According to a study published in the American Journal of Obstetrics and Gynecology, the incidence of severe perineal lacerations, including 3rd and 4th degree tears, is higher with assisted vaginal deliveries, such as forceps or vacuum extraction 3.
• The study found that assisted vaginal delivery was an independent risk factor for 3rd and 4th degree perineal lacerations, along with other factors such as maternal age, birth weight, and episiotomy 3.
• Another study published in the Journal of Family & Reproductive Health found that perineal massage during labor can reduce the risk of severe perineal trauma, including 3rd and 4th degree lacerations, by 48% 2.
• The use of mediolateral or lateral episiotomy with assisted vaginal births has also been shown to reduce the incidence of 3rd and 4th degree perineal lacerations by 43% and 68%, respectively 4.

Risk Factors for 3rd and 4th Degree Perineal Lacerations

• The risk factors for 3rd and 4th degree perineal lacerations with assisted vaginal birth include:
  • Primiparity 3, 4, 5
  • Mother's ethnicity 3, 5
  • Large for gestational age infants 3, 5
  • Certain interventions used in labor and birth, such as instrumental deliveries 3, 4, 5
  • Maternal age 3
  • Birth weight 3

Prevention and Management of 3rd and 4th Degree Perineal Lacerations

• Preventive practices with varying degrees of effectiveness include:
  • Antenatal perineal massage 2, 4, 5
  • Different maternal birthing positions 4, 5
  • Water births 5
  • Warm compresses 5
  • Protection of the perineum 4, 5
  • Episiotomy for instrumental births 4