Need for developing case definitions and guidelines for data collection, analysis, and presentation for primary postpartum haemorrhage as an adverse event following immunization:
Postpartum haemorrhage (PPH) describes excessive bleeding after delivery of a foetus. It is the leading cause of maternal death, responsible for approximately 68,500 deaths a year, 99.7% occurring in developing regions . It occurs in approximately 6% of deliveries when defined as a blood loss equal to, or greater than 500 ml, or 1–2% when a 1000 ml is used . It therefore represents a significant global health burden, disproportionately affecting those in the world’s poorest countries.
There is increasing interest into a broader role for vaccination in the prevention of neonatal and pregnancy-related infections. However, it is vital that all vaccines are monitored for their potential adverse effects, including their effect on key obstetric complications, such as postpartum haemorrhage. There is a need therefore for consensus on a unifying definition of postpartum haemorrhage to be used in vaccine trials, epidemiological and safety studies. Our case definition aims to standardize the definition for research and adverse event reporting. The purpose of this definition is not to establish new clinical indicators or thresholds for deciding when to treat post partum haemorrhage.
Postpartum haemorrhage is the consequence of several different pathologies that can occur in isolation or combination: uterine atony, genital tract trauma, retained placental tissue and coagulation dysfunction. In severe cases of postpartum haemorrhage often pathologies co-exist, with intractable haemorrhage often leading to coagulopathy. Uterine atony is regarded as the most common cause of PPH. It occurs when inadequate myometrial tone results in unchecked blood flow to the placental bed.
An individual’s risk of excessive blood loss will be influenced by numerous pre-existing, pregnancy-related and obstetric factors. Risk factors for PPH include: Asian ethnicity; obesity; previous PPH; multiple pregnancy; anaemia; large baby; placenta praevia; age over 40 years; induction of labour; prolonged labour; intrapartum pyrexia; placental abruption; episiotomy; operative vaginal delivery; retained placenta; and delivery by caesarean section . Incidence and severity of PPH will therefore vary widely depending on the population studied and the obstetric practice. PPH-related adverse clinical events will also vary depending on the individual. For example the same blood loss could have no clinical consequence in a healthy woman, but be a life-threatening event for in a woman with severe anaemia.
The accurate quantification of blood loss can be challenging. Estimation of blood loss has been shown to be inaccurate, with underestimation worsening at larger volumes , . Photometric methods, where the haemoglobin content of all swabs, drapes and pads at delivery is examined in laboratory, offer the greatest accuracy . The cost and logistics of these methods however mean they are used only in niche research studies. Direct measurement with an under-buttock, calibrated drape correlates with lab-based methods; although its accuracy depends on timely placement to collect blood without amniotic fluid or urine . Unfortunately the routine use of a calibrated drape is not associated with a decrease in severe PPH, therefore their routine use is mainly limited to research .