Study design, setting and population
This is a retrospective cohort study conducted at Virgen del Rocío University Hospital of Seville (a tertiary referral center with about 6000 births per year), including all women with uncomplicated MCDA pregnancies who had a birth at 32.0 – 37.6 weeks of gestation from January 2012 to December 2018.
Chorionicity was determined by first-trimester ultrasonography and confirmed after birth by pathological examination. In all cases a detailed anomaly scan was performed at 18.0 – 21.6 weeks. Specific management protocols for MCDA twins were determined locally following national and international guidelines, as those established by the Royal College of Obstetricians and Gynaecologists (RCOG)[24] or the International Society of Ultrasound in Obstetrics and Gynecology (ISUOG)[25].
Cases were classified into trial of labor (TOL) or PCS groups depending on the intended method of delivery. A TOL was planned if twin A was in vertex presentation after 32 weeks of gestation, estimated fetal weight was at least 1500 g, and there was no contraindication for vaginal delivery (non-vertex first twin, at least two previous CS, weight discordance > 15% when first twin was smaller, vasa previa, and/or any other condition like active herpes genital infection). Deliveries were included as TOL when the onset of labor was spontaneous or induced, and in all cases both fetuses were monitored intrapartum by continuous cardiotocography. In cases of non-vertex presentation of the second twin, breech extraction was performed by a senior obstetrician. The maximum time to perform an emergent CS was 10 minutes after decision.
A PCS was in most cases established when the first twin was in a non-vertex presentation. In no cases, a PCS was performed because of maternal request. At least two obstetricians and neonatologists were always present in the delivery room (from the second stage of labor) as well as in the operating room.