Trends and predictors of birth weight in Chilean children

Abstract

Objectives

Birth weight is an important public health indicator that reflects fetal health conditions and predicts future health. Identifying the most important factors related to birth weight would help defining preventive health strategies for both mothers and children. The objectives of this study are i. to describe, using a large birth database from a Chilean hospital, the trend of birth weight during 2002–2015, and ii. to determine factors during prenatal care associated with low and high birth weight.

Study design

This study is a secondary analysis of all single birth records at a Chilean Hospital in the southeast district of Santiago, Chile, during 2002–2015 (N = 78,931).

Methods

Sociodemographic information, clinical and obstetric history, lifestyle, and anthropometric variables were evaluated as potential predictors. Birth weight was categorized into five groups as per percentiles of weight as per gestational age. Data were extracted from clinical records. We used classification and regression tree methodology and logistic regression.

Results

The average birth weight for the period was 3316 g (SD 566), with little variation across time. Preterm births increased from 7% in 2002 to 10% in 2015, and births >40 weeks decreased from 10.7% in 2002 to 4.4% in 2015. The percentages of small and large for gestational age changed from 10.9% and 12.7% in 2002 to 9.9% and 13.9% in 2015, respectively. The predictors included in the optimal tree were body mass index, gestational weight gain, pre-eclampsia, and gestational diabetes. We found that women with a pregestational body mass index <28 kg/m², gestational weight gain <17 kg, and preeclampsia had a probability of 41% of having a small for gestational age neonate. Conversely, women with a body mass index ≥28 kg/m², gestational weight gain ≥17 kg, and gestational diabetes had a probability of 44% of having a large for gestational age neonate.

Conclusions

This study showed that the most important variables explaining birth weight are those related to maternal nutritional status. Thus, the strategies to promote a normal birth weight should aim for a normal maternal weight at the beginning of pregnancy, gestational weight gain within the recommendations, and prevention of gestational diabetes and pre-eclampsia.

Introduction

The World Health Organization defines birth weight (BW) as the first weight of the newborn just after birth.¹ BW is an important public health indicator because it reflects fetal and neonatal health conditions. Under the programming hypothesis, the fetus, which is highly plastic, adapts to adverse intrauterine factors such as malnutrition or hypoxia to ensure its immediate survival. This process is accompanied by reduced fetal growth that can lead, in some cases, to detrimental effects on postnatal health. Therefore, BW is in part an indicator of the intrauterine environment.²

Historically, health care professionals’ concern has been focused on babies with low BW (BW < 2500 g) and/or small for gestational age (SGA) due to their increased risk of morbidity (neurological, respiratory, gastrointestinal) and mortality.³ There is a solid body of evidence demonstrating an association between low BW and higher mortality rates from coronary heart disease and cardiovascular risk factors such as hypertension, type II diabetes mellitus, and hyperlipidemia.^4,5 Thus, the World Health Organization included as one of its goals for 2025 a 30% decrease in the prevalence of low BW.⁶

In the past two decades, there has also been increasing evidence that high BW (macrosomia, BW >4000 g or large for gestational age, LGA) is associated particularly with chronic noncommunicable diseases later in life, such as obesity, type II diabetes, and some types of cancer.^7,8 Although these associations are widely recognized, the evidence has not been conclusive.^9,10 It is important to note that these potential negative consequences of altered BW could be reversed/avoided by modifying their risk factors in early postnatal life.¹¹

Worldwide, the prevalence of low BW is 14.6% and varies across regions, with high values in the range of 11%–27% in South Asia and Africa.¹² By contrast, in developed countries and some developing countries, an elevated prevalence of macrosomia, in the range of 5%–20%, has been observed.^13,14 In Chile, a study that examined trends between 1991 and 2008 estimated a prevalence of 5.3% for low BW and 8.7% for macrosomia.¹⁵ It has been estimated that genetics accounts for 38%–80% of BW variation, whereas the environment might explain approximately 25%.¹⁶ Among the modifiable factors, we highlight maternal nutritional status, socioeconomic conditions such as educational level, marital status, psychological factors, smoking, inadequate access to health services, seasonality, access to good nutrition during pregnancy, and the presence of diseases such as anemia, high blood pressure, urinary tract infections, gestational diabetes mellitus (GDM), and pre-eclampsia.^7,17, 18, 19, 20 Increased maternal age has also been associated with variations in BW.²¹ We remark that there is growing evidence showing that preconception health is important not only for pregnancy outcomes but also for long-life health of their offspring. Thus, the relationship between prepregnancy obesity and the incidence of macrosomia has been widely studied.²²

Chile is a country that has experienced rapid epidemiological and nutritional transition, with a high prevalence of obesity, noncommunicable diseases, and their associated risk factors.²³ It is possible that some factors associated with BW variations have changed in the last two decades due not only to changes in their prevalence but also in their methods of screening and diagnosis. Identifying the magnitude and strength of the association of the most important factors related to BW will allow not only adequate planning of health resources but also the adoption of future preventive health strategies for both mothers and children.

The objectives of this study are i. to describe in a large sample of births in a Chilean hospital the trend of BW in the period between 2002 and 2015, and ii. to determine factors during prenatal care that are associated with a low or high BW.