Objective: The aim of this study is to identify perinatal factors influencing the condition of the second-born twin. 

Methods: A retrospective study of 15 years in a level 3 maternity center was conducted. 

Results: The study included 1,176 twin pairs. The birth was eutocic in 26.4% of first-born and 27.8% of second-born twins, but cesarean section was more frequent in second-born twins. The average weight of the first-born twin was 2,097 g and that of the second-born 2,060 g, and this difference was influenced by maternal age and conception mode; 14.5% of first-born twins and 20.1% of second-born twins were small for gestational age (GA). There was a statistically significant difference in the 1st and 5th minutes Apgar scores between twins and the score in the 5th minute was influenced by chorionicity. There was no statistically significant difference in the number of admissions to the Neonatal Intensive Care Unit, length of stay or number of neonatal deaths. There was a statistically significant difference in the number of disorders, influenced by maternal age. We also found a significant difference in hyperbilirubinemia, glycemic status and apnea, but not in other disorders. The number of patients who underwent at least 1 procedure was higher in second-born twins (27.7% vs 25.2%) and was influenced by chorionicity. There was a difference in surfactant administration, but not in other procedures. 

Conclusions: We found more cesarean sections in second-born twins, but more assisted vaginal deliveries in first-born twins. We also found statistically significant differences in relation to weight, size for GA, weight discordance, Apgar scores, and total number of disorders and procedures to which the twins were submitted. Chorionicity, conception mode and maternal age were of the most influence in these differences.