**7. Twin-to-twin delivery time intervals**

Another controversial subject about delivery in twins is the time interval between fetuses in vaginal delivery.

New guidelines such as the American College of Obstetricians and Gynecologists do not recommend an upper limit to the time interval between fetuses, if the fetal heart rate is reassuring, as some studies also suggests [44–47]. However, there are studies that provide evidence of an association, but not necessarily causality, between longer twin-to-twin time interval and poor second twin outcome, such as lower apgar grades and decreasing pH in umbilical arterial blood gas [48–50]. This lack of strong evidence leaves space for different approach and expectant management [51].

A very specific approach can be performed in the case of a dichorionic twin pregnancy with spontaneous preterm delivery <24 weeks and never above 28 weeks, which is called delayed interval delivery when the second twin do not have an indication for labor such as infection among other complications. Several techniques and interventions are described but the evidence is not strong, but the main goal is to provide a better outcome for the second twin, and success rates of these particular cases are good according to a systematic review of 2016 [52].
