# Temporal Patterns in Preterm Birth Subtypes and Perinatal Survival, 2000–2023: Population‐Based, Repeated Cross‐Sectional Time‐Series

## TL;DR

The study analyzed trends in preterm birth subtypes and perinatal survival in Hong Kong from 2000 to 2023, finding that while preterm birth rates increased, perinatal survival improved.

## Contribution

The study introduces a detailed classification of preterm birth subtypes to better understand trends and their impact on perinatal outcomes.

## Key findings

- Perinatal survival improved despite rising preterm birth rates.
- Subclassifying preterm birth revealed diverging trends among subtypes.
- Hypertensive disorders were the main cause of iatrogenic preterm birth.

## Abstract

Evaluate the rate and trend of preterm birth (PTB) and the associated perinatal survival in Hong Kong.

Population‐based, repeated cross‐sectional time series.

All public maternity hospitals.

845 640 singleton and 26 748 twin deliveries from 2000 to 2023.

Two analyses were performed (i) spontaneous PTB (sPTB) vs. iatrogenic PTB (iPTB), (ii) spontaneous PTB with no preterm prelabour rupture of membranes (PPROM) (sPTB‐noPPROM) versus. PTB following PPROM (PTB‐PPROM) vs. iPTB.

PTB rate and perinatal survival.

Simply dividing PTB into sPTB and iPTB demonstrated increasing PTB rates for both types amongst singleton and twin pregnancy. Subclassification of sPTB into sPTB‐noPPROM and PTB‐PPROM demonstrated a downward trend in sPTB‐noPPROM while PTB‐PPROM increased significantly (singleton: sPTB‐noPPROM average annual percent change (AAPC) −0.96, 95% CI −1.67 to −0.41; PTB‐PPROM AAPC 3.4, 95% CI 2.89 to 4.18; iPTB AAPC 2.01, 95% CI 1.57 to 2.45; twin: sPTB‐noPPROM AAPC −2.62, 95% CI −4.09 to −1.58; PTB‐PPROM AAPC 3.05, 95% CI 2.46 to 3.72; iPTB AAPC 2.75, 95% CI 1.82 to 3.69). PTB‐PPROM and iPTB were the leading causes of PTB for singleton and twin pregnancy, respectively. Hypertensive disorders were the predominant causes of iPTB for both singleton and twin pregnancy while iPTB indicated by maternal illnesses reduced over time. Reduction of neonatal mortality rates were noted amongst iPTB for singleton < 37 weeks and twin pregnancies at 34+0–36+6 weeks. The rate of stillbirth and perinatal mortality also reduced amongst PTB of twin pregnancies.

Perinatal survival improved despite increasing PTB rates. The trend of PTB should be interpreted in the context of perinatal health indicators, and categorisation of PTB could aid with truly reflecting and explaining the trends and patterns of PTB within a population.