Date Published: April 11, 2019
Publisher: Public Library of Science
Author(s): Andrea Mary Woolner, Dolapo Ayansina, Mairead Black, Sohinee Bhattacharya, Luca Giannella.
This study aimed to investigate the reproductive impact of a third- or fourth-degree tear in primigravid women. A retrospective population-based cohort study was conducted using data from Scottish Morbidity Records (SMR02). Primigravid women with a vaginal birth in Scotland from 1997 until 2010 were included. Exposure was third- or fourth-degree tear in the first pregnancy. The second pregnancy rate, interpregnancy interval and third- or fourth-degree tear in a second pregnancy were the primary outcomes. A nested case-control study was used to determine factors associated with repeat third- or fourth-degree tears in a second vaginal birth. Cox regression analysis and logistic regression were used to look for associations. Initial third- or fourth-degree tear occurred in 2.8% women (5174/182445). The percentage of third- or fourth-degree tears in first vaginal births increased from 1% in 1997 to 4.9% in 2010. There was no difference in having a second pregnancy (adjusted Odds Ratio (aOR) 0.98 (99%CI 0.89–1.09)) or the median interpregnancy interval to second pregnancy (adjusted Hazard Ratio (aHR) 1.01 (99%CI 0.95–1.08)) after an initial third- or fourth-degree tear. Women were over four times more likely to have a repeat injury in a subsequent vaginal birth (n = 149/333, aOR 4.68 (99% 3.52–6.23)) and were significantly more likely to have an elective caesarean section in their second pregnancy (n = 887/3333, 26.6%; 12.75 (11.29–14.40)). Increased maternal age and birthweight ≥4500g were risk factors for repeat injury. Third- and fourth-degree tears are increasing in Scotland. Women do not delay or avoid childbirth after initial third- or fourth-degree tear. However, women are more likely to have a repeat third- or fourth-degree tear or an elective caesarean section in the second pregnancy. Strategies to prevent third- or fourth-degree tears are needed.
Third- and fourth-degree tears are injuries which can occur to the perineum during vaginal birth. A third degree tear extends through the anal sphincter muscle complex.[1–3] A fourth degree tear extends into the rectal mucosa.[1–3] Together they are often known as OASIS (Obstetric Anal Sphincter InjurieS).[1–3] Incidence of such tears appears to be rising with 5.9% of first pregnancies affected in England and Wales in 2012. Both third and fourth degree tears can cause distressing symptoms such as faecal incontinence[3,5–8] and sexual dysfunction.[6,9] Childbirth following such a tear risks worsening symptoms[5,7,8] and repeat OASIS injury in a subsequent pregnancy.[4,10–18] However, evidence of the effect an initial third or fourth degree tear has on subsequent pregnancy and birth, including the risk of repeat injury, is limited. Consequently, it is difficult to advise women on future birth options. Women are offered either vaginal birth or elective caesarean section after such tears with little evidence to support either decision. Women may delay or avoid future childbirth due to fears over repeat injury, but evidence on time to next pregnancy is sparse. More information is needed so that women can make informed decisions about their second birth following an initial third- or fourth-degree tear.
The study included 182,445 women with first vaginal births in Scotland between 1997 and 2010. The population sample is illustrated in Fig 1. 5174 (2.8%) of women had a third- or fourth-degree tear in their first pregnancy. 131015 (71.8%) women had a spontaneous vaginal birth whereas 3541 (19.4%) had a forceps delivery and 15347 (8.4%) had a ventouse delivery for their first vaginal birth. Second pregnancies were recorded between 1998 and 2015 in 122,014 women. Fig 2 shows the percentage of third- and fourth-degree tears over time for all women with first and second vaginal births in Scotland from 1997–2015. Over time the percentage of first vaginal births which resulted in a third- or fourth-degree tear has increased from 1% in 1997 to 4.9% in 2010. Similarly, the rate of third- or fourth-degree tears in second vaginal births is increasing, with 0.2% in 1999 to 1.5% in 2015, though the trajectory is less marked. Table 1 shows the baseline characteristics of the women in their first pregnancy according to exposure status. Women with an initial third- or fourth-degree tear were more likely to be older. However, there was no difference in BMI or socioeconomic deprivation between the exposed and unexposed groups. Notably, women without an initial third- or fourth-degree tear were more likely to be smokers. Table 1 also demonstrates the proportion of women who had a second birth and the odds of having a second birth according to tear status in the first vaginal birth. Women with an initial third- or fourth-degree tear were less likely to have a second pregnancy recorded with a difference of 2.5% (crude OR 0.89 (99% CI 0.83–0.96). However, this was not statistically significant when adjusted for potential confounders (aOR 0.98 (99%CI 0.89–1.09)).
Third- and fourth-degree tears are an increasing obstetric issue and can affect subsequent mode of delivery. Improving the prevention of these injuries needs to be prioritised.