Introduction

Low birth weight (LBW) is a high risk for children's health and also an indicator of a public-health problem in under developing countries. LBW is defined as a birth weight of a live born infant less than 2,500 g, regardless of gestational age. LBW is either caused by preterm birth (which is defined as younger than 37 weeks of gestational age) or the infant being small for gestational age, or a combination of both. Subcategories of preterm birth include early preterm (24 0/7–33 6/7 weeks of gestation) and late preterm (34 0/7–36 6/7 weeks of gestation) (1). SGA is defined as growth at the 10th or less percentile for weight of all fetuses at that gestational age (2). Prematurity and SGA are associated with neonatal and infant mortality and morbidity, and some disorders such as dysfunction of immune system in adulthood (2, 3). LBW reflects not only situation of health and nutrition, but also indicates survival rate, psychosocial and health growth and development. Intrauterine malnutrition sometimes sustains in all life time by causing hypotonicity. It also increases higher incidence of diabetes and heart disease, cognitive disorders and lower IQ (3) in adulthood. LBW incidence ranges from 8.1% in developed countries and 30-60% in under developing countries. The incidence of SGA neonates is one third of LBW neonates (2). Subcategories of LBW include Very Low Birth Weight (VLBW) which is less than 1500 g, and Extremely Low Birth Weight (ELBW) which is less than 1000 g. VLBW is a precise index for predicting neonatal death. It includes more than 50% of neonatal death rate and 50% of morbidities and neurological disabilities (4).  

Previous studies have been assessed different factors like smoking, socio-economic situation, and consuming Chlorinated water in induction of LBW and SGA neonates (5, 6). Since we have not found any study about the incidence rate of LBW, SGA and VLBW and their relationship with family's socio-economical situation in Sabzevar, the present study aimed to assess the incidence of LBW and SGA and their related factors in Sabzevar in 2011.

Materials and Methods

This prospective descriptive-analytic study was conducted on low birth weight neonates born in Mobini academic hospital of Sabzevar, Iran, 2011 to 2012. Participants were 481 LBW neonates by consensus sampling. The research was confirmed by research committee of Sabzevar University of Medical Sciences. Informed consents were obtained from parents of admitted neonates. Then data were gathered by 2 expert nurses who occupied in NICU by using a researcher-made checklist. The checklist was confirmed by content validity and internal consistency (Cronbach's alpha (α=0.81)) reliability. The checklist includes some neonatal characteristics such as: weight, gender, Apgar score, birth priority, anomaly in neonate, multiple pregnancy, delivery type, gestational age, etc; and maternal information like  perinatal problems (diabetes, preeclampsia, heart disease, renal disease, etc), drug history, addiction, smoking, prenatal nutrition, and socioeconomic status.

Weight (W), height (H) and head circumference of neonates were measured initially at birth. Neonates' weight was measured by a Seca scale with an accuracy of 5 g. Anthropometric indices (weight, height, head and abdomen circumference) were charted on standard curves of neonatal growth according to gestational age. Neonatal percentiles <10% were classified as SGA (small for gestational age) and percentiles 10-90% were classified as AGA (appropriate for gestational age). Gestational age was calculated first according to LMP (Last Menstrual Period) if it was valid and then sonography, especially if it was done before 20 w of GA. Ponderal index (PI)[1] was calculated for each neonate and its percentile was determined according to standard curves mentioned in text books. The checklists were completed by one of nurses before discharge of the neonates.  

   Data were coded and analyzed by descriptive and analytic [one-way analysis of variance (ANOVA), t-test] statistics and confidence interval 95% by SPSS-11.5. P < 0.05 was considered significant.

Results

480 (6.33%) newborns were LBW (out of 7599 births). 275 neonates (57.4%) were female (table 1).

Table 1: Frequency of maternal demographic and socio-economical situation

Mean weight of LBW neonates was 2039.1±9.6 g (table 2). The lowest weight of neonates was 440 g and the most weight was 2490 g. The least and the most gestational age was 23 w vs. 40 w.

Table 2: Mean of Demographic Variables in mothers and neonates

12.7% (62 neonates) were VLBW and 5% (24 neonates) were ELBW (Out of 480 LBW neonates).

280 neonates (58.3%) were preterm and 200 neonates were 37-40 w (out of LBW neonates). Preterm rate was 3.8% in 2011 (out of total newborns).

162 (34.1%) of LBW neonates were SGA. SGA rate was 2.2% in 2011 (out of total newborns). 306 (64.4%) and 7 (1.5%) of LBW neonates were AGA and LGA, respectively (table 3) (Chart 1). 18% of SGA neonates were symmetric SGA (HC and BW lower than 0^th percentile). Mean of PI was 2.21±0.023 in SGA group vs. 2.21±0.013 (Chart 1).

Table 3: Frequency of LBW and SGA, AGA and LGA in each group of gestational age

Mean weight of neonates was respectively 1174.4±36.8 and 2182.2±12.9 in 1500 g groups. There was not a significant difference between mother's age and weight in these two groups (Table 4).

Table 4: Mean of some variables in two groups of neonatal weight

Mothers' urinary infection incidence was 18.3% in VLBW neonates vs. 4.4% in non-VLBW neonates.

Family income (p-value=0.026) and mother's education (p-value=0.004) were significantly lower in SGA neonates in comparison with the other LBW neonates. The incidence of mothers' urinary infection in VLBW neonates was significantly higher than non-VLBW neonates (p-value<0.001). Inadequate nutrition and low BMI of mothers were more in SGA neonates, but there was no significant relationship (p-value>0.05).

 There was not a significant relationship between neonatal gender and birth priority with VLBW and ELBW; but there was a significant relationship between gender (p-value=0.024) with weight percentile. Female neonates had lower percentiles.

There was not a significant relationship between VLBW with deformity of organs, cord diameter, multi-pregnancy, mother's addiction, mother's education, place of residence, prenatal care, and heavy work during pregnancy; but there was a siginificant relationship between VLBW with prenatal difficulties (p-value<0.001), maternal problrms (p-value<0.001) and neontal apgar (p-value<0.001). Among mentioned variables, there was just a significant relationship between ELBW with cord diameter (p-value<0.001), prenatal difficulties (p-value=0.002), maternal problems (p-value<0.001) and neonatal apgar (p-value<0.001).

There was a significant relationship between GA with neonatal apgar (p-value<0.001).