Vela, GMeyer, JHMeyer, MP2026-05-192026-05-192025-11-21Australian and New Zealand Journal of Obstetrics and Gynaecology, ISSN: 0004-8666 (Print); 1479-828X (Online), Wiley, 66(1), e70065-. doi: 10.1111/ajo.700650004-86661479-828Xhttp://hdl.handle.net/10292/21122Background: Neonatal alloimmune thrombocytopaenia (NAIT) is a rare but potentially serious condition where maternal antibodies result in destruction of foetal and neonatal platelets. At Middlemore Hospital in south Auckland, routine cord blood platelet counts were performed over many years. Aims: These were twofold: To determine the prevalence of severe thrombocytopaenia (TP) and severe NAIT and investigate platelet counts in siblings of infants with TP. Materials and Methods: Cord blood was collected on all hospital births over 500 g over a 12-year period (2005–2016) and term infants with TP (< 150 × 10⁹/L) selected. Records of infants with severe TP (< 50 × 10⁹/L) were reviewed for potential NAIT cases. Records of siblings of infants with any degree of TP were also reviewed to examine the potential for NAIT in affected families. Results: Of 68910 births, 62083 platelet counts were suitable for analysis and 641 term infants had TP (1%) with 16 having severe TP (0.025%). NAIT or potential NAIT was judged clinically to be present in half of these (0.013%). Most cases were of European ethnicity with a Maori infant and a Tongan infant also being possible cases. No serious complications were identified. 5% of siblings of infants with TP had low counts with only one infant having a likely diagnosis of severe NAIT. Conclusions: Severe TP was uncommon amongst infants born in south Auckland where mothers of Maori and Pacific Island ethnicity make up the majority of the population. Performance of routine cord platelet counts was of limited value in detecting potential cases of severe NAIT.© 2025 The Author(s). Australian and New Zealand Journal of Obstetrics and Gynaecology published by John Wiley & Sons Australia, Ltd on behalf of Royal Australian and New Zealand College of Obstetricians and Gynaecologists. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.https://creativecommons.org/licenses/by/4.0/cord bloodneonatal alloimmune thrombocytopaenia (NAIT)newborn infantplatelet antigensthrombocytopaenia3213 Paediatrics32 Biomedical and Clinical SciencesInfant MortalityPediatric Research InitiativeClinical ResearchPerinatal Period - Conditions Originating in Perinatal PeriodHematologyStem Cell Research - Umbilical Cord Blood/ PlacentaStem Cell ResearchReproductive health and childbirth3 Good Health and Well Being1114 Paediatrics and Reproductive Medicine1117 Public Health and Health ServicesObstetrics & Reproductive Medicine3215 Reproductive medicine4204 MidwiferyFetal BloodHumansPlatelet CountPrevalenceCohort StudiesSiblingsPregnancyInfant, NewbornNew ZealandFemaleMaleThrombocytopenia, Neonatal AlloimmuneHumansThrombocytopenia, Neonatal AlloimmuneNew ZealandInfant, NewbornPlatelet CountFemaleFetal BloodMaleCohort StudiesPrevalencePregnancySiblingsJournal ArticleOpenAccess10.1111/ajo.70065