title: Haemoglobin discordances in twins: due to differences in timing of cord clamping?
abstract: 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.
authors.affiliation: Division of Neonatology, Department of Pediatrics, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Lianne
authors.initials: L
authors.lastname: Verbeek
authors.affiliation: Division of Neonatology, Department of Pediatrics, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Depeng P
authors.initials: DP
authors.lastname: Zhao
authors.affiliation: Department of Obstetrics, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Johanna M
authors.initials: JM
authors.lastname: Middeldorp
authors.affiliation: Department of Obstetrics, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Dick
authors.initials: D
authors.lastname: Oepkes
authors.affiliation: Ritchie Centre, Hudson Institute of Medical Research, Melbourne, Victoria, Australia.|Department of Obstetrics and Gynaecology, Monash University, Melbourne, Victoria, Australia.
authors.forename: Stuart B
authors.initials: SB
authors.lastname: Hooper
authors.affiliation: Division of Neonatology, Department of Pediatrics, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Arjan B
authors.initials: AB
authors.lastname: Te Pas
authors.affiliation: Division of Neonatology, Department of Pediatrics, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Enrico
authors.initials: E
authors.lastname: Lopriore
mesh_terms: D016022:Case-Control Studies; D017707:Erythrocyte Transfusion; D005260:Female; D006454:Hemoglobins / Q000032:analysis*; D006801:Humans; D010920:Placenta / Q000098:blood supply*; D011247:Pregnancy; D059285:Pregnancy, Twin / Q000502:physiology; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic; D014470:Umbilical Cord / Q000098:blood supply*
chemical_list: D006454:Hemoglobins
keywords: Cord clamping; Dichorionic twins; Hemoglobin; Monochorionic twins; Vaginal birth