The World Health Organization (WHO) defines low birth weight (LBW) as a birth weight of less than 2500 grams, regardless of gestational age [1]. LBW can be caused by preterm birth (birth before 37 weeks of gestation), small size for gestational age (defined as weight for gestation 10th percentile), or both. More than 80% of neonatal deaths occur in LBW newborns, two-thirds of whom are preterm, and one-third are term small for gestational age [2]. The new-born’s chances of survival, healthy growth and development were heavily influenced by birth weight [3]. LBW is a significant public health issue in every country, with a variety of short- and long-term consequences affecting human capital [2].

Despite the precautions, numerous studies in various parts of the world have revealed the factors that contribute to LBW, classified as maternal, paternal, and obstetrical factors [4-6]. However, the risk factors for LBW varied greatly across geographical settings. Thus, the main aim of this study was to determine the prevalence and associated risk factors of LBW among term newborns in Bandar Abbas, Iran.

We retrospectively assessed singleton term pregnant mothers who gave birth at Khaleej-e-Fars Hospital (a tertiary hospital) in Bandar Abbas, Iran, between January 1^st, 2020, and January 1^st, 2022. Using electronic patient records, data were extracted by trained collectors from the "Iranian Maternal and Neonatal Network (IMaN Net)," a valid national system. This study complies with the Declaration of Helsinki and was performed according to ethics committee approval. The Ethics and Research Committee of the Hormozgan University of Medical Sciences approved the study. The records of all patients who provided informed consent for using their data for research purposes were analyzed. In cases of illiteracy, their legal guardians provided informed consent. Statistical analysis was performed with patient anonymity following ethics committee regulations. Demographic factors (age, educational level, residency place, medical insurance, access to prenatal care facilities, smoking status), obstetrical factors (gestational age, parity, new born sex, oligohydramnios, preeclampsia, gestational diabetes mellitus (GDM), abnormal placentation, placenta abruption), and maternal comorbidities (overt diabetes mellitus, chronic hypertension, cardiovascular disease, thyroid dysfunction, drug addiction, hepatitis, anemia, infertility, and COVID-19 at the time of admission) were extracted from electronic data of each mother. Mothers were divided into groups: those with LBW newborns (less than 2500 grams) and those with normal weight newborns (2500-4000 grams).

The IBM Statistical Package for the Social Sciences Statistics, version 25, was used to examine the data (IBM Corp, Armonk, NY). Categorical variables are presented as numbers and frequencies (%). The Chi-square test was used to compare differences between the groups for categorical variables. Logistic regression models were used to assess LBW associated risk factors. The result was presented as odds ratio (OR) or adjusted odds ratio (aOR) after adjusting for confounders and 95% confidence interval (CI). P < 0.05 was considered statistically significant, and all statistical tests were two-tailed.

Of 7440 singleton term deliveries during the study period, 460 (6.2%) were LBW. The demographic characteristics of the study population are presented in Table 1. Maternal age was the only demographic factor that was significantly different between groups.

Table 1: Maternal characteristics of study population.

Data are presented as n (%).

LBW: Low birth weight.

NW: Normal weight.

Table 2 shows the obstetrical differences between mothers with LBW newborns and those with normal weight (NW) newborns. It was discovered that those who had LBW newborns differed from those who had NW newborns in terms of parity, the frequency of preeclampsia, and new born sex.

Table 2: Obstetrical factors and maternal comorbidities of the study population.

Data are presented as n (%). LBW: Low birth weight. NW: Normal weight.

In bivariate analysis, maternal age, parity, new born sex, and preeclampsia were significantly associated with LBW. Mothers at the age of 13-19 aOR 1.97 (CI 1.26-12.98), primiparous mothers aOR 2.44 (CI 2.01-3.17), mothers with female fetus aOR 3.79 (CI 2.13-3.99), and mothers diagnosed with preeclampsia aOR 1.71 (CI 1.35-2.99) were at higher risk of having LBW in multivariate analysis (Table 3).

Table 3: Factors associated with low birth weight.

OR: Odds Ratio

aOR: adjusted Odds Ratio

The global prevalence of LBW is 15.5%, meaning that approximately 20.6 million such infants are born each year, with 96.5% being born in developing countries [2]. South Asia has the highest prevalence of LBW (31%), followed by the Middle East and North Africa (15%), Sub-Saharan Africa (14%), and East Asia and the Pacific (7%) [1]. Our study found a lower prevalence of LBW (6.2%) because we only included term pregnancies, whereas global estimates of LBW are regardless of gestational age. Along with several other studies [7,8], adolescent mothers had a higher risk of having LBW newborns than those between the ages of 20 and 34. It has been suggested that pregnant adolescents are more likely to develop high blood pressure, such as preeclampsia, which can lead to premature labor and delivery. Furthermore, it has been suggested that adolescents are less aware of pregnancy-related problems and are less likely to seek medical care [7]. However, our study found no link between maternal care attendance and LBW.

According to several studies, mothers who live in rural areas have a higher risk of having LBW babies than urban residents [7,9]. However, no differences were discovered in our study. This is because rural areas have less access to prenatal care facilities in many countries than urban areas. In Iran, many accessible facilities for mothers, even in rural areas, make access to maternity care possible. According to our findings, only 1% of our study population did not have access to prenatal care. Cigarettes are one of the most commonly used drugs during pregnancy, linked to LBW. The mechanisms by which smoking causes adverse effects during pregnancy are not entirely understood. Nicotine is most likely a factor. Nicotine decreases uteroplacental circulation, resulting in lower maternal weight gain and, as a result, adverse fetal outcomes such as small size for gestational age and LBW [10]. In contrast to previous findings [11,12], smoking was not linked to LBW in our study. This could be due to the low prevalence of smokers in our study population, which could impact the study's findings. Only 0.6% of our study population were smokers.

In accordance with a previous study [13], LBW was more common in baby girls. In terms of maternal comorbidities, several studies have found a link between anemia and LBW [7,8]. Micronutrient deficiency during pregnancy has been linked to serious consequences for the developing fetus and thus birth weight. Severe anemia may interfere with normal intrauterine growth by impairing oxygen delivery to the fetus [8]. However, our study found that the risk of LBW was similar in anemic and non-anemic mothers. Preeclampsia is one of the risk factors for LBW. The result of our study supports previous studies [14,15]. There are two main reasons for this. First, preeclampsia increases the risk of pregnancy termination at a younger gestational age. Second, in cases of preeclampsia, uteroplacental blood flow may be impaired, affecting fetal growth. It should be noted, however, that in the current study, all mothers were full term, and the cause of LBW was not prematurity. Other maternal comorbidity including cardiovascular disease, chronic hypertension, thyroid dysfunction, diabetes, COVID-19, hepatitis, and placenta abnormalities were not associated with LBW. The strength of our study is that our study registers are of high quality and in accordance with childbirth records. We investigated various factors associated with LBW in pregnancies. The population study sample size was large enough to reflect the situation regarding identifying risk factors of LBW. Our study was conducted retrospectively, which is still a limitation. The database did not allow for the precise timing of the various events during pregnancy. More data was missing for variables, such as body mass index and weight gain during pregnancy.

LBW has been linked to several factors. Significant predictors of LBW were found to be maternal age, parity, new born sex, and preeclampsia. Health care providers should focus on identifying factors to address the problem of LBW.

F.D. wrote the proposal. M.S. and M.S.J. contributed significantly to data collection. The findings were analysed and interpreted by F.D., who wrote the manuscript. V.M. was the primary contributor to the manuscript's commenting and writing. A.R. and F.P. assessed the manuscript's scientific content critically. The final manuscript for submission was read and approved by all authors.

Competing Interests

The authors declare that they have no competing interests.

Funding

None.

Availability of Data and Materials

The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request.

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