Low Birth Weight: Prevalence and Risk Factors

Background: World Health Organization defines Low birth weight as a birth weight of less than 2500gm. Low birth weight babies have higher mortality, have impaired academic achievements, and increased risk of cardiovascular disease and diabetes. Aim: This study aims to define low birth weight, estimate it’s prevalence and study it’s correlation with maternal age, weight, height and haemoglobin levels, gender of the baby, seasonal variations. Results: 29 out of 200 (14.5%) of babies were found to have low birth weight (Chart 1). 20 out of 29 (68.96%) low birth weight babies were delivered by Caesarean section as compared to 9 (31.03%) babies who were born by normal delivery. Maternal age was analysed and it was observed that 9 patients (31.03%) aged less than 20 years, 8 patients (27.58%) were in the age bracket of 21-30 years and 12 patients (41.37%) belonged to the age group between 31-40 years (Chart2). The sex of low birth weight babies was studied and it was observed that 20 (68.96%) low birth weight babies were females as against 9 (31.03%) male babies. 17 patients (58.62%) who delivered low birth weight babies were primigravidae as compared to 12 patients (41.37%) who were multigravidae.3 patients (10.34%). had maternal weight of less than 50kg, 17 patients (58.62%) had weight between 51-55kg and 9 patients (31.03%) had weight of more than 55kg. Maternal height was studied and it was observed that 23 patients (79.31%) had a height in the range of 151-160cm and only 6 patients (20.68%) who delivered low birth weight babies had height measuring more than 160 cm. Haemoglobin levels of patients with low birth weight babies were observed to find that 5 patients (17.24%) had haemoglobin levels of less than 10 gm%, 12 patients (41.37%) had haemoglobin levels between 10.1-11gm% and 12 patients (41.37%) had a haemoglobin level of more than 12.1 gm%. Analysis of seasonal variation amongst low birth weight babies was done and it was observed that 13 babies (44.82%) were born between March to May, 8 babies (27.58%) were born between the months of June to September and 8 babies (27.58%) were delivered between the months of October to February. 12 (41.37%) of the low birth weight babies were pre term whereas 17 babies (58.62%) delivered after full term.


Introduction
The birth weight of an infant is the first weight recorded after birth taken within the first few hours after birth. World Health Organization defines Low birth weight as a birth weight of less than 2500gm [1]. There are two more entities viz. very low birth weight when the birth weight is <1500 gm and extremely low birth weight when the birth weight is <1000gm [1]. Pre term birth and intrauterine growth retardation may lead to low birth weight and 15-20% of births are low birth weight. Low birth weight has an inverse relationship with socioeconomic status and it is important to study low birth weight because it is a valuable public health indicator of maternal health, healthcare delivery, nutrition and poverty. Low birth weight babies have a 20 times greater risk of dying as compared to those with birth weight of more than 2.5kg [2], have impaired academic achievements, and increased risk of cardiovascular disease and diabetes. Infants with low birth weight are not capable of adapting themselves outside the womb and are at a greater risk of mortality [3].

Aim
This study aims to define low birth weight, estimate it's prevalence and study it's correlation with maternal age, weight, height and haemoglobin levels, gender of the baby, seasonal variations. Association between low birth weight and Caesarean section, parity and preterm babies was also studied.  [4]. 20 out of 29 (68.96%) low birth weight babies were delivered by Caesarean section as compared to 9 (31.03%) babies who were born by normal delivery. Low birth weight is one of the causes of adverse pregnancy outcomes in both premature and full-term infants and increases the rate of Caesarean section [5].

Chart 1: Prevalence of low birth weight babies.
(Chart 2) Maternal age was analysed and it was observed that 9 patients (31.03%) aged less than 20 years, 8 patients (27.58%) were in the age bracket of 21-30 years and 12 patients (41.37%) belonged to the age group between 31-40 years (Chart2). A study by Mondal has shown a correlation between risk of low birth weight in mothers under 19 and over 35 years of age [6]. Chart 2: Chart depicting maternal age of those who had delivered low birth weight babies.
The sex of low birth weight babies was studied and it was observed that 20 (68.96%) low birth weight babies were females as against 9 (31.03%) male babies. A Japanese study revealed a significant association between low birth weight and female baby [7]. 17 patients (58.62%) who delivered low birth weight babies were primigravidae as compared to 12 patients (41.37%) who were multigravidae. 3 patients (10.34%). had maternal weight of less than 50kg, 17 patients (58.62%) had weight between 51-55kg and 9 patients (31.03%) had weight of more than 55kg. Maternal height was studied and it was observed that 23 patients (79.31%) had a height in the range of 151-160cm and only 6 patients (20.68%) who delivered low birth weight babies had height measuring more than 160cm. Haemoglobin levels of patients with low birth weight babies were observed to find that 5 patients (17.24%) had haemoglobin levels of less than 10gm%, 12 patients (41.37%) had haemoglobin levels between 10.1-11gm% and 12 patients (41.37%) had a haemoglobin level of more than 12.1gm%. Analysis of seasonal variation amongst low birth weight babies was done and it was observed that 13 babies (44.82%) were born between March to May, 8 babies (27.58%) were born between the months of June to September and 8 babies (27.58%) were delivered between the months of October to February. The large annual temperature range may contribute to the low birth weights during summer months [8]. 12 (41.37%) of the low birth weight babies were preterm whereas 17 babies (58.62%) delivered after full term.

Discussion
Low birth weight may be because of preterm or intrauterine growth restriction or both. 2500g is the cut-off which defines low birth weight. Low birth weight is a risk factor for increased perinatal mortality and adverse infant outcomes. It is one of the major determinants of perinatal survival, infant morbidity, and mortality [9]. Deaths in low birth weight babies is 20 times higher than among infants of normal weight [10] and it is the most important indicator of infant mortality during the first few months of life [11]. Maternal age less than 20 years is commonly associated with low birth weight [12]. Teenage pregnancy and history of abortion has also been observed to be associated with low birth weight [13]. Similarly unwanted and unplanned pregnancies have been seen to be associated with low birth weight [14].
Maternal nutritional status, maternal weight, gestational age, pre-eclampsia, intervals between pregnancies, parity, multiple births, educational status, lack of antenatal care (ANC) and low socio-economic status have all been studied to have a correlation with low birth weight [15]. Short stature, anaemia and/or micronutrient deficiencies in mothers is also associated with low birth weight [16]. Low socio-economic status leads to inadequate food intake by the pregnant woman, lack of hygiene and sanitation, restricted access to medical care and iron and folic acid supplementation during pregnancy leading to low birth weight [17]. Lack of education of mother is also associated with low birth weight because illiteracy leads to indulgence in smoking, drug or substance abuse [18].
Maternal height also has a bearing on baby being low birth weight. Short statured mothers have low birth weight babies and the cut off in height of Indian mothers have been established at 145cm [19]. The relationship between maternal haemoglobin level and birth weight has also been proven and low maternal haemoglobin has been established to be associated with low birth weight [20].

Conclusion
The prevalence of low birth weight in this study has been estimated to be 14.5% which is comparable to the values in other Indian studies of about 20%. Low birth weight was more often seen in babies delivered by Caesarean section as compared to babies who were born by normal delivery. Low birth weight is one of the causes of adverse pregnancy outcomes in both premature and full-term infants and increases the rate of Caesarean section. A correlation has been confirmed between risk of low birth weight in mothers below 20 years and above 35 years of age. Teenage pregnancies, unwanted and unplanned pregnancies have more chances of delivering low birth weight babies.

a)
Female babies have been more often found to have low birth weight in comparison to male babies. Primigravidae have been observed to more frequently deliver low birth weight babies as compared to multiparae mothers. Maternal malnourishment, short stature, low socio economic status, poor education of mother, anemia, lack of basic hygiene and sanitation facilities and ante natal care have all been associated with low birth weight.n