A new study has found that women going for vbac were more likely to have a 3rd or 4th degree perineal tear (anal sphincter injury), than women having their first baby, and concluded that people should be told of the increased risk. It was a retrospective study looking at all births in a region over 5 years 2009-14.
Let's unpick it a little.
The study did account for variations such as age, BMI, whether there was an episiotomy, epidural, baby's birth weight, and 'mode of birth' (vaginal birth without help, vaginal birth assisted by forceps or ventouse, caesarean birth).
It did not account for:
First timers are cared for differently than women going for vbac, who have much more stringent rules on timing, monitoring, etc.
Position giving birth in. Peeps going for vbac are encouraged to have continual electronic ctg monitoring, and therefore are most likely to give birth lying down, resulting in increased chance of tear.
Fear. Women going for vbac, and their care givers, have increased fear about the process. There is research that shows fear increases the chance of tearing.
Who's giving the care. Midwife led care is associated with fewer tears, compared to Obstetric led care. Women going for vbac are usually under obstetric led care, women having their first baby are usually under midwife led care.
Place of birth. You are much less likely to have a anal sphincter injury at home or in a birth centre. First timers are more likely to give birth in a midwife led unit or home than those going for vbac, though more and more people planning vbacs are planning to have home births.
How you are cared for, where you give birth, what position, and how you feel about it all, are important.
Having a vbac may increase your chance of a significant tear, but there are things you can do about it.
A last note on numbers. The study concluded that there was a 21% increased risk of severe perineal injury. It is not good practise to use percentages like this, nor to use relative stats. It is better to use actual numbers, so you can compare like to like. The study found the number of 3rd/4th degree tears was:
5.7 in 100 of first timers (so 94.3 in 100 didn't have a significant injury)
7.1 in 100 of VBACs (92.9 in 100 didn't have one)
So it is still a small chance, and although there is an increase the number is still small.
It is also worth noting that the number of these significant perineal injuries is a lot higher in this study that in the UK at that time. The large UK Birth Place Study 2011 found the rate, for low risk people, to be
3.2 in 100 for obstetric led units (labour ward) and alongside units,
2.3 for standalone units and
1.9 for home births.
(Table created by me, from the study data published.)
I hope you found this helpful. I'd be interested to hear what you think.