Abstract
BackgroundThe incidence of preterm birth (PTB, < 37 weeks of gestation) has been increasing in China and many other countries in recent years. However, the causes of the increase were not well understood. The current study aims to examine the contribution of maternal age, period of delivery, and maternal birth cohorts to long-term trends in preterm birth in Guangzhou, China.MethodsIn a retrospective population-based study, data were obtained from 2,535,000 singleton live births with 20–43 gestational weeks from 2001 to 2016 and recorded in the Guangzhou Perinatal Health Care and Delivery Surveillance System, in China. The age-period-cohort models were applied to investigate the temporal changes in incidences of PTB, stratified by parity.ResultsThe incidence of preterm birth steadily increased from 5.1% in 2001 to 5.9% in 2016, with larger rise in primiparous mothers (from 5.0 to 5.9%) compared to multiparous mothers (from 5.6 to 5.9%). A J-shaped and a V-shaped relationship were found between maternal age and PTB among primiparous and multiparous mothers, respectively. A linear cohort effect was found among primiparous mothers with the lowest risk of PTB [risk ratio (RR) = 0.81, 95% confidence interval (CI): 0.74 to 0.89] in 1961 and the highest risk (RR = 1.06, 95% CI: 1.00 to 1.13) in 1997 compared to the mothers born in 1981. An inverse U-shaped association between maternal birth cohort and PTB was found in multiparous mothers. There were weak decreasing period effects on the trend of overall PTB among multiparous mothers and on the trend of extremely (< 27 weeks) or very (28–31 weeks) PTB among both parity groups during the period of 2001–2012.ConclusionsOur findings showed the PTB incidences had been increasing in the past 16 years in Guangzhou, China and both maternal age and cohort effects contributed to these trends. Further studies are recommended on the impact of altered maternal age and parity on premature births and corresponding public education and public health policies.
Highlights
The incidence of preterm birth (PTB, < 37 weeks of gestation) has been increasing in China and many other countries in recent years
Our findings showed the Preterm birth (PTB) incidences had been increasing in the past 16 years in Guangzhou, China and both maternal age and cohort effects contributed to these trends
The overall incidence steadily increased from 5.1% in 2001 to 5.9% in 2016 with an average annual increase of 8.2‰ [95% confidence interval (CI), 6.9‰ to 9.4‰], among which the incidence increased from 5.0% in 2001 to 5.9% in 2016 in primiparous mothers and from 5.6 to 5.9% in multiparous mothers
Summary
The incidence of preterm birth (PTB, < 37 weeks of gestation) has been increasing in China and many other countries in recent years. The current study aims to examine the contribution of maternal age, period of delivery, and maternal birth cohorts to long-term trends in preterm birth in Guangzhou, China. A classic age-period-cohort analysis, simultaneously examining maternal age (age effect, reflecting biological changes and social processes) [14], delivery year (period effect, capturing change given a specific period such as advance in medical services, health policies), and the birth year of mothers (cohort effect, reflecting unique experience/exposure and contextual factors experienced by the cohort over their life time) [15], is a useful tool to interpret trends of health outcomes [14, 16, 17]. Most previous studies examining the association of maternal age and delivering period with incidence of PTB did not take into account the role of maternal birth cohorts [5, 6, 18]. One study in the United States has explored the interaction among maternal age, period, and birth cohort and found a strong effect of maternal age and period on PTB and a weak effect of cohort among older African American mothers [11]
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