Benefits of the «en caul¼ technique for extremely preterm breech vaginal delivery.

INTRODUCTION: The "en caul" technique, i.e. delivery with intact membranes, may reduce the risk of obstetric trauma in vaginal breech delivery of extreme preterm infants. We aimed at comparing perinatal mortality and morbidity among extremely preterm breech vaginal deliveries between infants delivered "en caul" and those with "ruptured membranes". MATERIAL AND METHODS: We performed a fourteen-year retrospective study in a tertiary university center. All vaginal deliveries of singleton breech live infants with an antenatal decision of active resuscitation between 24 weeks and 27+6 weeks were included. Perinatal outcomes were compared between the "en caul" group, with intact membranes at the onset of pushing efforts and the "ruptured membranes" group, with ruptured membranes at the onset of pushing efforts. The primary outcome was perinatal mortality defined by intrapartum or neonatal death. The secondary outcomes were fetal extraction difficulties, arterial pH and 5 min Apgar score. RESULTS: We included 52 infants in the "en caul" group and 71 in the "ruptured membranes" group. The perinatal mortality rate did not differ between the two groups (19.2% in the "en caul" group versus 28.2% in the "ruptured membranes" group, p = 0.25). The mean arterial pH at birth was higher in the « en caul ¼ group (7.32 ± 0.1 vs 7.24 ± 0.1, p = 0.001). There were no differences between the groups for fetal extraction difficulties, especially fetal head entrapment (9.6% versus 9.9%). CONCLUSION: Even though the "en caul" technique does not seem to decrease the perinatal mortality rate, it remains a simple technique, which could improve neonatal morbidity.

Optical linewidth of a passively mode-locked semiconductor laser.

We measured the optical linewidths of a passively mode-locked quantum dot laser and show that, in agreement with theoretical predictions, the modal linewidth exhibits a parabolic dependence with the mode optical frequency. The minimum linewidth follows a Schawlow-Townes behavior with a rebroadening at high power. In addition, the slope of the parabola is proportional to the RF linewidth of the laser and can therefore provide a direct measurement of the timing jitter. Such a measurement could be easily applied to mode-locked semiconductor lasers with a fast repetition rate where the RF linewidth cannot be directly measured.