Tryptase negative Anaphylaxis, an interesting case in the context of major obstetric haemorrhage Abstract: Anaphylaxis during pregnancy, labour and delivery can be catastrophic for the mother and baby. During the first three trimesters, aetiologies are similar to those in non-pregnant women. During labour and delivery, common aetiologies are beta-lactam antibiotics, latex, and other agents used in medical and peri-operative settings, including less commonly blood products. Anaphylactic transfusion reactions are more frequent with components containing a high volume of plasma. In most cases, the exact cause is unknown. We report a case of a 35 year old lady who had her 4th caesarean section for a twin pregnancy. She had a combined spinal and epidural (CSE) and after a 1.7L blood loss intraoperatively was taken to recovery for monitoring. The patient continued to bleed in recovery where she was resuscitated. During resuscitation, she developed an anaphylactic reaction. The anaphylaxis was dealt with, but ongoing bleeding meant the patient had to return to theatre. She had a hysterectomy and later required uterine artery embolisation. The patient returned to theatre on two further occasions due to persistent bleeding. In this case report, we discuss anaphylaxis in the context of major obstetric haemorrhage. The cause of anaphylaxis remained undetected and the tryptase levels were within normal limits.