Objective: To develop an international definition for hyperemesis gravidarum to assist in clinical diagnosis and harmonize hyperemesis gravidarum definition for study populations.Study design: A mixed-methods approach was used to identify potential hyperemesis gravidarum definition criteria (i.e. systematic review, semi-structured interviews and closed group sessions with patients and Project Steering Committee input). To reach consensus on the definition we used a webbased Delphi survey with two rounds, followed by a face-to-face consensus development meeting, held in Windsor UK, and a web-based consultation round, in which the provisional hyperemesis gravidarum definition was fed back to the stakeholders. Four stakeholder groups were identified 1) researchers; 2) women with lived experience of hyperemesis gravidarum and their families; 3) obstetric health professionals (obstetricians, gynecologists, midwives); and 4) other health professionals involved in care for women with hyperemesis gravidarum (general practitioners, dieticians, nurses). To reflect the opinions of the international community, stakeholders from countries in all global regions were invited to participate.Results: Twenty-one identified potential criteria entered the Delphi survey. Of the 277 stakeholders invited, 178 completed round one, and 125 (70%) also completed round two. Twenty stakeholders attended the consensus development meeting, representing all stakeholder groups. The consultation round was completed by 96 (54%) stakeholders, of which 92% agreed with the definition as presented. The consensus definition for hyperemesis gravidarum consisted of: start of symptoms in early pregnancy (before 16 weeks gestational age); nausea and vomiting, at least one of which severe; inability to eat and/ or drink normally; strongly limits daily living activities. Signs of dehydration were deemed contributory for the definition for hyperemesis gravidarum. Conclusions: The proposed definition for hyperemesis gravidarum will help clinical studies to achieve more uniformity, and ultimately increasing the value of evidence to inform patient care.

Objective To develop a core outcome set for trials on the treatment of hyperemesis gravidarum (HG). Design Identification of outcomes is followed by a modified Delphi survey combined with a consensus development meeting and a consultation round. Setting An international web‐based survey combined with a consensus development meeting. Population Stakeholders including researchers; women with lived experience of HG and their families; obstetric health professionals; and other health professionals. Methods We used systematic review, semi‐structured patient interviews, closed group sessions and Steering Committee input to identify potential core outcomes. We conducted two web‐based survey rounds, followed by a face‐to‐face consensus development meeting and a web‐based consultation round. Main outcome measures A core outcome set for research on HG. Results Fifty‐six potential outcomes were identified. The modified Delphi process was completed by 125 stakeholders, the consensus development meeting by 20 stakeholders and the consultation round by 96 stakeholders. Consensus was reached in ten domains on 24 outcomes: nausea; vomiting; inability to tolerate oral fluids or food; dehydration; weight difference; electrolyte imbalance; intravenous fluid treatment; use of medication for hyperemesis gravidarum; hospital treatment; treatment compliance; patient satisfaction; daily functioning; maternal physical or mental or emotional wellbeing; short‐ and long‐term adverse effects of treatment; maternal death; pregnancy complications; considering or actually terminating a wanted pregnancy; preterm birth; small for gestational age; congenital anomalies; neonatal morbidity and offspring death). Conclusions This core outcome set will help standardise outcome reporting in HG trials. Tweetable abstract A core outcome set for treatment of hyperemesis gravidarum in order to create high‐quality evidence.