RT Journal Article SR Electronic T1 Haemoglobin discordances in twins: due to differences in timing of cord clamping? JF Archives of Disease in Childhood - Fetal and Neonatal Edition JO Arch Dis Child Fetal Neonatal Ed FD BMJ Publishing Group Ltd and Royal College of Paediatrics and Child Health SP fetalneonatal-2016-311822 DO 10.1136/archdischild-2016-311822 A1 Lianne Verbeek A1 Depeng P Zhao A1 Johanna M Middeldorp A1 Dick Oepkes A1 Stuart B Hooper A1 Arjan B Te Pas A1 Enrico Lopriore YR 2016 UL http://fn.bmj.com/content/early/2016/12/09/archdischild-2016-311822.abstract AB Objective Our objective was to study the differences in haemoglobin (Hb) at birth in dichorionic (DC) versus monochorionic (MC) twins in relation to birth order and mode of delivery.Methods All consecutive DC twin pregnancies and uncomplicated MC twin pregnancies with two live-born twins delivered at our centre were included in this retrospective cohort study. Hb levels at birth and on day 2 were evaluated in association with birth order and mode of delivery. The occurrence of polycythaemia (venous haematocrit >65%) was also recorded.Results A total of 300 DC and 290 MC twin pairs were included. In DC and MC twins delivered vaginally, second-born twins had a higher Hb level at birth compared with their co-twin (mean Hb level 16.7 vs 15.9 g/dL (p<0.01) in DC twins and 17.8 vs 16.1 g/dL (p<0.01) in MC twins). In twins delivered through caesarean section, no intertwin differences in Hb levels were detected. Polycythaemia occurred significantly more often in second-born twins compared with first-born twins delivered vaginally: 10 (5%) vs 2 (1%) (p=0.02) in DC twins and 20 (12%) vs 2 (1%) (p<0.01) in MC twins.Conclusions Second-born DC and MC twins delivered vaginally have higher Hb levels at birth compared with first-born twins. Intertwin Hb differences in MC twins may partly be related to blood transfusion through the vascular anastomoses. Since DC twins do not have anastomoses, other factors may lead to Hb differences, including differences in timing of umbilical cord clamping.