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.
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Contributors All authors are responsible for reported research, and all authors have participated in the concept and study design, analysis and interpretation of data, drafting or revising of the manuscript, and have approved the manuscript as submitted. LV conceptualised and designed the study, collected data, carried out a part of the initial analyses, drafted initial manuscript and approved the final manuscript as submitted. DPZ collected data, carried out a part of the initial analyses, critically reviewed the manuscript and approved the final manuscript as submitted. EL conceptualised and designed the study, coordinated and supervised data collection, critically reviewed the manuscript and approved the final manuscript. JMM, DO, SBH and ABTP contributed to the interpretation of data, reviewed and revised the manuscript and approved the final manuscript as submitted.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.
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