Socio-economic inequalities in low-birth weight, full-term babies from singleton pregnancies in Taiwan

Summary

Objectives

This study investigated the chronological trend of low-birth weight in full-term babies (TLBW) in Taiwan in the 1980s and 1990s when the nation experienced a rapid economic advancement, and assessed the association between TLBW and parental education and marital status.

Design

Data from liveborn singletons from Taiwan's birth registry, born between 1978 and 1997, were used to calculate overall and socio-economic factor-specific rates of TLBW for every 2-year interval in this 20-year period.

Methods

Logistic regression models were used to assess the trend of TLBW rates, and the interaction between secular time, selected demographic factors and other predictors.

Results

Among 6,159,070 full-term, liveborn singletons, 208,729 were TLBW. The average annual rate of TLBW was 3.39% in the study period. The period-specific TLBW declined monotonically from 4.41% in 1978–1979 to 2.49% in 1996–1997, representing a 43% deduction. Multiple logistic regression demonstrated persistent declining trends irrespective of the educational level or marital status of the parents. However, the decline was slower for populations of lower socio-economic status, such as less-educated parents and unmarried mothers, which enhanced the inequalities of TLBW risk across populations. The TLBW risk ratios of the least-educated mothers to the most-educated mothers increased from 1.43 in 1978–1979 to 2.05 in 1996–1997. Unmarried status was an independent predictor of elevated risk of TLBW.

Conclusions

The association between socio-economic inequality and the risk of TLBW infants was sustained over the 1980s and 1990s in Taiwan. Interventions are necessary to promote antenatal care and educational attainment, particularly for lower socio-economic and socially deprived populations in Taiwan.

Introduction

Low-birth weight (LBW) (<2500 g) is associated with increased risk of morbidity1, 2, 3 and mortality4, 5 during infancy. There is also growing evidence that the adverse consequences of LBW may continue throughout the life cycle.6, 7, 8 Increased LBW rates have been noted in many parts of the world. In the USA, the percentage of LBW births increased from 6.7% in 1984 to 7.8% in 2002,⁹ and the LBW rate increased by 11% between 1993 and 2000 in England and Wales.¹⁰ LBW is thus a worldwide concern. Comprehensive epidemiological evidence suggests an association between socio-economic status and risk of LBW; lower maternal socio-economic status is an important predisposing factor for LBW in full-term babies (TLBW).¹¹

The rapid economic growth experienced in Taiwan during the 1980s and 1990s greatly improved social welfare and community health. Gross national product per capita increased from US $1577 in 1978 to US $13,559 in 1997, and the number of health personnel per 10,000 population increased from 21.12 to 66.72 in the same period. The improvement in community health led to an increase in life expectancy (from 71.74 to 74.68 years) and a decrease in the infant mortality rate (from 8.86 to 6.35‰) during the same period.¹² These two health indicators are often used to measure the health of populations.¹³ Nonetheless, the improvement in public health resulting from socio-economic prosperity was not ubiquitous. Some Taiwanese studies conducted during this period proposed geographic variations in morbidity¹⁴ and mortality.¹⁵

This study used data from Taiwan's birth registry to examine the secular trend of LBW (<2500 g) prevalence in full-term (⩾37 completed weeks of gestation) live births between 1978 and 1997. Particular attention was focused on the association between socio-economic status and TLBW.