Mode of Delivery: What's the second twin got to do with it?

How should an expecting mother plan to deliver if she has twins? Many people think that twins mean an automatic cesarean birth. Not true! As long as the presenting (or first) twin is head down (aka vertex), a vaginal delivery is likely safe and beneficial to both mother and babies. (Of course, every situation is unique, and these important decisions must be individualized with the help of a doctor or midwife.)

Even though vaginal delivery is a safe option for many twin pregnancies, planned c-section because of twins is still commonplace. Dr. Easter and colleagues from the Brigham and Women’s Hospital at Harvard wanted to know if the presentation (head first or butt first) of the second twin affected providers’ willingness to support a trial of labor. (Study link here) The authors collected data on 716 twin pregnancies from 2007 to 2011 at their hospital. For all of these women, the first twin was head-first at >32 weeks gestation and thus they were likely good candidates for a vaginal delivery. The second twin was either also head-first or was not-head-first. Second twins who were not head-first (aka nonvertex) could be butt-first (breech) or be lying on their side (transverse). In both scenarios, experienced obstetricians can help guide the second twin out, for instance, through a procedure called “breech extraction.”  The authors excluded any women who had a reason not attempt labor and vaginal delivery, such as a uterine scar, and any pregnancies with a lethal fetal anomaly.

Of the 716 women, all of whom were eligible to try for a vaginal delivery, only 49% attempted labor. 73% of women with the second twin head-first underwent a trial of labor, and only 17% of women with the second twin not-head-first attempted a trial of labor. The authors’ hypothesis was correct. Women with the second twin in the head-first position were statistically significantly more likely to attempt trial of labor.

The authors also found that the rate of successful vaginal delivery was not significantly different between second twins who were head-first or not after controlling for confounders. 85% of not-head-first second twins delivered vaginally, and 70% of head-first second twins delivered vaginally. For non-vertex second twins, a provider with increasing years of experience was associated with a higher rate of vaginal delivery.

Mothers tended to fair equally well regardless of presentation, except for one measure: cervical lacerations. 8% of mothers with a not-head-first second twin suffered a cervical laceration, and only 1% of mothers with a head-first second twin did.

Perhaps most interestingly, in 11% of cases the second twin’s position changed during labor. This research suggests that making delivery decisions based on the position of the second twin is not necessarily the best way to go. It would be better to use the information to plan accordingly for the delivery, for instance, by ensuring that experienced staff are available to support the birth.