Fetal scalp blood sampling and risk factors for hypoxic ischemic encephalopathy

Liljeström, L. 2018. Birth asphyxia. Fetal scalp blood sampling and risk factors for hypoxic ischemic encephalopathy. Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine 1435. 81 pp. Uppsala: Acta Universitatis Upsaliensis. ISBN 978-91-513-0250-8. Preventing birth asphyxia is a major challenge in delivery care. The aims of this thesis were to evaluate fetal scalp blood sampling (FBS) and explore risk factors for moderate to severe neonatal hypoxic ischemic encephalopathy (HIE). In a study of 241 deliveries monitored by FBS, a discrepancy between pH and lactate (one abnormal and one normal value) was common (55%) in combined FBS. We found that the frequency of operative deliveries for fetal distress (ODFD) was lower when both pH and lactate were analysed in FBS compared with analysis of only pH or lactate, without affecting neonatal outcome. (Study I) In a questionnaire study, women (n = 51) monitored by FBS generally tolerated the test well. Women without epidural, with higher body mass index (BMI), and with less cervical dilatation had higher pain ratings compared with their counterparts. The obstetricians that performed the test generally experienced the test as easy to perform, but more complicated with high maternal BMI, less cervical dilatation, and higher station of the fetal head. (Study II) In a national cohort of 692 428 live births ≥ 36 weeks, risk factors for moderate to severe HIE were identified. We found a linear association between increasing maternal BMI and decreasing maternal height and risk of HIE. Compared with non-short (≥156 cm) and normal weight (BMI<25 kg/m) women, short and overweight women had a threefold risk of HIE. (Study III) Obstetric emergencies occurred in 29% of HIE cases, more commonly in parous (37%) than in nulliparous (21%) women. Among nulliparous women, shoulder dystocia was most common, with the strongest association to HIE. In parous women without previous caesarean, shoulder dystocia was most common, but placental abruption had the strongest association to HIE. Among parous women with previous caesarean, uterine rupture was the most prevalent, with the strongest association to HIE. (Study IV) Conclusions: Combined FBS might decrease the frequency of ODFD. FBS is well tolerated in women and generally uncomplicated for the obstetrician to perform. Women with short stature and overweight have increased risk of having an infant with HIE. Obstetric emergencies are common underlying causes of HIE, especially in parous women.