Trends in preterm birth in singleton deliveries in a Hong Kong population

To examine trends in preterm birth and its relationship with perinatal mortality in Hong Kong.

In a retrospective cohort study, data were reviewed from singletons delivered between 1995 and 2011 at a university teaching hospital. Trends in preterm birth (between 24 and 36 weeks of pregnancy), perinatal mortality, and subtypes of preterm birth (spontaneous, iatrogenic, and following preterm premature rupture of membranes [PPROM]) were examined via linear regression.

There were 103 364 singleton deliveries, of which 6722 (6.5%) occurred preterm, including 1835 (1.8%) early preterm births (24-33 weeks) and 4887 (4.7%) late preterm births (34-36 weeks). Frequency of preterm birth remained fairly consistent over the study period, but that of spontaneous preterm birth decreased by 25% (β=-0.83; P<0.001), from 4.5% to 3.8%. Frequency of preterm birth following PPROM increased by 135% (β=0.82; P<0.001), from 0.7% to 1.7%. The perinatal mortality rate decreased from 56.7 to 37.0 deaths per 1000 deliveries before 37 weeks (β=-0.16; P=0.54). Early preterm birth contributed to 16.0% of all deaths.

Although the overall rate of preterm birth in Hong Kong has remained constant, the frequencies of its subtypes have changed. Overall perinatal mortality is gradually decreasing, but early preterm birth remains a major contributor.