What is the increased maternal risk associated with the combination use of vacuum and forceps for delivery compared to using either method alone?

The combination use of vacuum and forceps during delivery is associated with an increased risk of obstetric anal sphincter injuries (OASIS) when compared to the use of either method alone. OASIS includes third and fourth-degree lacerations, which can significantly impact maternal morbidity by resulting in complications such as pelvic floor dysfunction, urinary incontinence, and anal incontinence.

Using both techniques together can lead to higher forces being applied during delivery and can complicate the delivery process, thereby increasing the likelihood of severe perineal trauma. The risks are particularly pronounced when both devices are used, as this dual approach may not only compound the forces applied but also can affect the delivery pathway, increasing the chance of tissue tearing.

In contrast, the other options may imply lower or unchanged risks. For instance, a lower incidence of OASIS would not be supported by evidence that shows an increase in injury rates when combining these methods. Similarly, claiming that the risk profiles are similar to using a single method overlooks the documented increased risk associated with using dual mechanisms for delivery. Lastly, suggesting that there is only an increased risk of fetal trauma through this combined use fails to account for the significant maternal risks like OASIS that have been well established in clinical studies