Stillbirth rate in singleton pregnancies: a 20-year retrospective study from a public obstetric unit in Hong Kong

Although the stillbirth rate is low in Hong Kong, up to 50% of stillbirths have unclassifiable causes and up to one third of stillbirths have unexplained causes. This retrospective study investigated the underlying causes of singleton stillbirths in Hong Kong.

This study examined the prevalences and causes of stillbirths in a university tertiary obstetric unit between 2000 and 2019. Medical records were reviewed for all singleton pregnancies complicated by stillbirths. Causes of stillbirth were determined via clinical assessments and laboratory findings, then compared between 2000-09 and 2010-19.

Overall perinatal mortality significantly decreased by 16.7%, from 5.52/1000 in 2000-09 to 4.59/1000 in 2010-19; the singleton stillbirth rate slightly decreased (from 3.27/1000 to 2.91/1000). These changes were related to early prenatal diagnostic improvements concerning congenital malformations and genetic disorders. Pre-eclampsia prevalence among singleton pregnancies increased from 1.5% to 1.7% because of increasing maternal age; the stillbirth rate among patients with pre-eclampsia decreased from 2.5% to 1.4%. Foetal growth restriction of unknown cause contributed to 16% of all stillbirths; this prevalence did not change over time. Moreover, foetal growth restriction was not diagnosed during routine antenatal care in 43.5% of patients. Thirty-six percent of all stillbirths were unexplained. The prevalences of stillbirth associated with chorioamnionitis and placental abruption did not change over time.

Causes of stillbirth in Hong Kong have changed in the past 20 years because of altered demographic characteristics and improved prenatal testing. Further improvements should focus on early foetal growth restriction detection and preeclampsia prevention.