Department of Paediatrics and Puericulture, Faculty of Medicine, Federal University of Rio Grande do Sul, Hospital de Clìnicas de Porto Alegre, Porto Alegre, Brazil.
J Biosoc Sci. 2010 Mar;42(2):243-53. doi: 10.1017/S002193200999037X. Epub 2009 Oct 26.
The strong association of very low birth weight (VLBW; <1500 g) with infant mortality is well known. There are no data related to VLBW trends in Brazil although findings from some large surveys carried out in small- and medium-sized cities have demonstrated an increase in low birth weight (LBW; <2500 g) rates over the last 30 years. The aim of this study was to evaluate the secular trend of VLBW in the city of Porto Alegre, a large city in a developed area in southern Brazil, and the potential determinants of this trend during the 1990s and early 2000s. This is a registry-based study. Data were obtained from birth certificates of all live births in the city from 1994 to 2005. The variables analysed were: VLBW as the dependent variable and maternal age and schooling, type of delivery, type of hospital, number of live births, gestational age, newborn gender and unemployment rate. The incidence ratio rate (IRR) using Poisson regression was calculated to identify possible trends in VLBW rates. Poisson regressions were performed in order to assess the influence of some independent variables on VLBW. A total of 257,740 singleton newborns were delivered in the city during the period, with a steady reduction in the total number of live births per year from 23,296 in 1994 to 18,325 in 2005. The results showed a small but significant increase in VLBW (p for trend=0.049). There was a significant trend towards adequacy for gestational age per birth weight, suggesting a reduction in rates of intrauterine growth restriction (IUGR) (p<0.001). The findings showed a significant increase of 1% per year in the probability of VLBW. The main risk factors were related to VLBW mothers with low levels of schooling, public hospitals and multiparity and nulliparity. After adjustment, nulliparity remained as a significant risk factor. The interaction between type of hospital and type of delivery indicated that the probability for VLBW was 3.6 times higher (p<0.001) among those born in public hospitals by Caesarean section than those born in private hospitals by vaginal delivery. The results show that southern Brazil is going through a demographic transition characterized by a significant decrease in number of live births associated with a small increase in VLBW rates, a decrease in IUGR rates and stabilization of LBW.
极低出生体重（VLBW；<1500 克）与婴儿死亡率之间的强关联是众所周知的。尽管一些在中小城市进行的大型调查结果表明，过去 30 年来低出生体重（LBW；<2500 克）的发生率有所增加，但巴西并没有与 VLBW 趋势相关的数据。本研究旨在评估巴西南部发达地区城市阿雷格里港的 VLBW 的时间趋势，并评估 20 世纪 90 年代和 21 世纪初这一趋势的潜在决定因素。这是一项基于登记的研究。数据来自 1994 年至 2005 年该市所有活产儿的出生证明。分析的变量是：VLBW 为因变量，母亲年龄和受教育程度、分娩类型、医院类型、活产儿数量、胎龄、新生儿性别和失业率。使用泊松回归计算发病率比值比（IRR）以确定 VLBW 发生率的可能趋势。进行泊松回归以评估一些独立变量对 VLBW 的影响。在这段时间内，该市共有 257740 名单胎新生儿出生，每年活产总数稳步减少，从 1994 年的 23296 人减少到 2005 年的 18325 人。结果显示，VLBW 略有但有统计学意义的增加（趋势 P 值=0.049）。与出生体重相比，胎龄适宜性呈显著趋势，表明宫内生长受限（IUGR）发生率降低（P<0.001）。研究结果显示，VLBW 的可能性每年增加 1%。主要危险因素与低教育水平、公立医院和多胎及初产妇的 VLBW 母亲有关。调整后，初产妇仍为显著危险因素。医院类型和分娩类型之间的相互作用表明，剖宫产出生于公立医院的 VLBW 发生的可能性是阴道分娩出生于私立医院的 3.6 倍（P<0.001）。结果表明，巴西南部正在经历人口转变，其特征是活产总数显著减少，同时 VLBW 发生率略有增加，IUGR 发生率下降，LBW 稳定。
