Abstract
Low birth weight (LBW) is a major predictor of child mortality and morbidity. The objectives of this study are to determine the proportion and risk factors of LBW. A matched case-control study was conducted at Omdurman Maternity Hospital, Sudan. The study population consisted of all babies delivered in August 2016 excluding stillbirths, multiple births, and babies with insufficient data. All LBW neonates were selected using total coverage sampling as cases and matched on babies’ gender with randomly selected normal birth weights as controls. The sample size was 350 babies; 175 test cases and 175 control cases. Data were collected from hospital records and six risk factors were tested: mother age, parity, gravidity, mode of delivery, hypertensive disorders, and diabetes mellitus. The proportion of LBW was 10.8% of the total number of delivered neonates which is 2,938. The bivariate analysis identified that younger mother age (p = 0.03) and hypertension (p = 0.02) were significantly associated with LBW while other factors were found statistically insignificant. Multivariable conditional logistic regression revealed that hypertensive disorders in pregnancy increase the risk for LBW almost three times [Adjusted OR = 2.98 (95% CI: 1.23–7.22), p = 0.02]. We found that hypertension is an independent risk factor for LBW. The proportion of LBWcan be reduced if hypertension is controlled by providing simple measures like proper antenatal care and health education for pregnant women.
Keywords: Low birth weight, Risk factors, Matched case control, Sudan
INTRODUCTION
Low birth weight (LBW) is defined by the World Health Organization (WHO) as a birth weight of less than 2,500 g (5.5 pounds) [1]. LBW results from either prematurity (birth before 37 weeks of gestation) and/or intrauterine growth restriction (IUGR) [1]. The WHO reported that the prevalence of LBW is 15.5% or approximately 20 million of all births and that about 95% of them were born in developing countries [1]. LBW levels in sub-Saharan Africa are around 15% [1].
LBW is strongly associated with child morbidity and mortality and contributes to a range of poor health outcomes [2]. LBW is now known to be associated with increased rates of coronary heart disease and related disorders, stroke, hypertension, and adult-onset diabetes. Also, it contributes to growth impairment and poor cognitive development, including cerebral palsy, learning disabilities, and visual problems [3,4].
Risk factors of LBW are many, but all revolve around prematurity and intra-uterine growth restriction (IUGR; one study identified and enumerated 43 risk factors) [5]. Those are – to list a few examples – socioeconomic status, gravity, parity, maternal age, diabetes mellitus (DM), hypertension, maternal anemia, and antenatal care [5]. LBW is a good indicator of public health problems, including long-term maternal illness and inadequate health care. It also represents a significant predictor of newborn health and survival [1].
In Sudan, there are few studies published about LBW prevalence and risk factors. This study aimed to study the proportion and risk factors of LBW in Omdurman Maternity Hospital, Khartoum State, Sudan.
MATERIALS AND METHODS
Study design and setting
This study is a hospital-based, retrospective matched case-control study conducted at Omdurman Maternity Hospital in Khartoum State, Sudan. Omdurman Maternity Hospital was established in 1957, and the nursery unit was created in 1977. This hospital is a public healthcare facility providing specialized obstetrics and gynecology inpatient and outpatient services as well as medical care of newborns, and it is the largest tertiary hospital and training center for midwives in Khartoum state.
Cases and controls definition
Cases were defined as newborns delivered at Omdurman Maternity Hospital in August 2016 with a birth weight of less than 2,500 g. Newborns delivered with a birth weight more than or equal to 2,500 g were defined as controls. The study population included singleton newborns delivered at term without any congenital malformation. The matching process was made based on the sex and age of the newborns using simple random sampling techniques giving an equivalent number of controls. All registered deliveries in Omdurman Maternity Hospital in the study period were included (=2,938 newborns). We found that the total number of newborns delivered with a birth weight less than 2,500 g was 316 and 141 LBW newborns were excluded because of: stillbirth (n = 24), multiple births (n = 74), and lack of sufficient data (n = 43). Finally, there were a total of 175 eligible LBW newborns included for the bivariate and multivariate analysis. The process of cases and controls selection was summarized in a flow chart in Figure 1.
Figure 1.
Flow chart showing the process of cases and controls selection. LBW, Low birth weight.
Data collection and variable definitions
The lists and data of deliveries were obtained from the Hospital Information and Statistics System, where each mother’s health-record is saved, containing information about the whole pregnancy period from the antenatal period until delivery, and the status of the mother and her baby during and after delivery. The information obtained was entered into a standardized data sheet and included the following: obstetrics information including mother age, gravidity, parity, mode of delivery, medical problems including hypertension and DM, and information about the neonates including birth weight, sex, and health condition of the newborn.
The predictor variables included in this study were selected based on the availability of the data collected from the records. Maternal age was defined as the age of the mother at the time of delivery. Gravidity was defined as the number of all previous pregnancies, including abortion and stillbirths, while parity was defined as the number of the last successful pregnancies, including stillbirths but not miscarriages. Maternal hypertension in this study was defined as all hypertensive-related illnesses, which include essential hypertension, gestational hypertension, pre-eclampsia, and eclampsia. DM was defined as pre-existing DM and gestational DM.
Data analysis
The Statistical Package for Social Sciences software version 23 was used for data analysis. First, descriptive statistics were done to show the distribution of data in terms of frequencies and means. Second, bivariate analysis was done to study the associations and risks in terms of p-values and odds ratios using McNemar’s test, which is designed for the paired categorical data. The paired t-test was used for comparison of the continuous variables with a normal distribution. Third, variables with significant associations were adjusted in a multivariate conditional logistic regression analysis for matched case-control studies to eliminate the effect of the potential confounders and to identify the independent effect of the risk factors. The significance level for all analyses was set as p-value <0.05.
RESULTS
Descriptive statistics and bivariate analysis
A total of 2,938 neonates were delivered at Omdurman Maternity Hospital during the study period. Among them, the total number of babies delivered with LBW was 316 newborns, giving a proportion of 10.8% as LBW. As shown in Figure 1, the complete data of 350 neonates (175 cases of LBW and 175 controls) were included for further analyses. The LBW neonates had a lower mean of maternal age and higher rates of nulliparity, primigravidity, cesarean delivery, and maternal hypertension than normal birth weight babies (Table 1).
Table 1.
Characteristics of the normal and LBW neonates included in the study.
| Variables | Total | Cases | Controls | ||||
|---|---|---|---|---|---|---|---|
| No. (%) | Mean (SD) | No. (%) | Mean (SD) | No. (%) | Mean (SD) | ||
| Birth weight (kg) | - | 2.59 (0.65) | - | 2.04 (0.37) | - | 3.15 (0.34) | |
| Mother age (years) | - | 27.81 (6.01) | - | 27.12 (6.04) | - | 28.51 (5.93) | |
| Sex | Male | 162 (46.3%) | - | 81 (46.3%) | - | 81 (46.3%) | - |
| Female | 188 (53.7%) | - | 94 (53.7%) | - | 94 (53.7%) | - | |
| Maternal parity | Nulliparous | 110 (31.4%) | - | 59 (33.7%) | - | 51 (29.1%) | - |
| Multiparous | 240 (68.6%) | - | 116 (66.3%) | - | 124 (70.9%) | - | |
| Maternal gravidity | Primigravida | 104 (29.7%) | - | 54 (30.9%) | - | 50 (28.6%) | - |
| Multigravida | 246 (70.3%) | - | 121 (69.1%) | - | 125 (71.4%) | - | |
| Mode of delivery | Vaginal | 217 (62.0%) | - | 104 (59.4%) | - | 113 (64.6%) | - |
| Caesarean | 133 (38.0%) | - | 71 (40.6%) | - | 62 (35.4%) | - | |
| Maternal DM | Yes | 5 (1.4%) | - | 1 (0.6%) | - | 4 (2.3%) | - |
| No | 345 (98.6%) | - | 174 (99.4%) | - | 171 (97.7%) | - | |
| Maternal HTN | Yes | 26 (7.4%) | - | 19 (10.9%) | - | 7 (4.0%) | - |
| No | 324 (92.6%) | - | 156 (89.1) | - | 168 (94.0%) | - | |
DM, Diabetes mellitus; HTN, Hypertension; SD, Standard deviation.
The bivariate analysis results presented in Table 2 display both concordant and discordant pairs for categorical variables studied, with the crude odd ratios and the associations using McNemar’s test. The only categorical variable found significantly associated with LBW was maternal hypertension (p = 0.02). The other risk factors: nulliparity, primigravidity, and maternal DM did not show a statistically significant association with LBW.
Table 2.
McNemar’s table for the associations between the categorical variables and LBW.
| Cases (n = 175) | Controls (n = 175) | Crude OR | p value | ||
|---|---|---|---|---|---|
| es | No | ||||
| Nulliparous | Yes | 19 | 40 | 1.25 | 0.35 |
| No | 32 | 84 | |||
| Primigravida | Yes | 19 | 35 | 1.13 | 0.62 |
| No | 31 | 90 | |||
| Maternal DM | Yes | 0 | 19 | 2.71 | 0.19 |
| No | 7 | 149 | |||
| Maternal HTN | Yes | 0 | 1 | 0.25 | 0.02 |
| No | 4 | 170 | |||
DM, Diabetes mellitus; HTN, Hypertension; OR, Odd Ratio.
A paired t-test was conducted to determine the association between the continuous predictor variable (mother age) and LBW. The mean age for mothers was significantly lower (t = −2.17, p = 0.03) among the mothers of LBW neonates (27.12 ± SD. 6.04) compared to the mean age for the control group (28.51 ± SD. 5.93) as shown in Table 3.
Table 3.
Univariate analysis using paired t test showing association between LBW and mother age among neonates delivered at Omdurman Maternity Hospital, Omdurman, Sudan, August 2016.
| Variables | Mean (SD) Cases controls | Mean difference (SD) | t | p value |
|---|---|---|---|---|
| Mother age | 27.12 (6.04) 28.51(5.93) | −1.39 (5.98) | −2.17 | 0.03 |
SD, Standard deviation.
Logistic regression analysis
Conditional logistic regression analysis was done for the factors that were found statistically significant (mother age and maternal hypertension) to eliminate the effect of potential confounders and to identify the independent effect of the risk factors. The analysis revealed that hypertension is a potential predictor of LBW, with almost three times higher risk of LBW when compared to non-hypertensive mothers [Adj OR = 2.98 (95% CI: 1.23–7.22), p-value = 0.02]. Mother age showed a significant association with LBW in the multivariable logistic regression analysis [Adj OR = 0.96 (95% CI: 0.92–0.99), p-value = 0.02] as shown in Table 4.
Table 4.
Multivariable conditional logistic regression showing associations of LBW with mother age and hypertension among neonates delivered at Omdurman Maternity Hospital, Omdurman, Sudan, August 2016.
| Variables | B | Adj OR | 95%CI | p value |
|---|---|---|---|---|
| Mother age | −0.042 | 0.96 | 0.92–0.99 | 0.02 |
| Hypertension | 1.093 | 2.98 | 1.23–7.22 | 0.02 |
B, Unstandardized regression coefficient; Adj OR, Adjusted odds ratio; 95% CI, 95% Confidence interval.
DISCUSSION
The current study in August 2016 investigated the proportion and risk factors of LBW in a public maternity hospital in Khartoum State, Sudan. The proportion of LBW infants in this study was 10.8%, showing a lower prevalence compared to the rate of 31% reported previously in the Safe Motherhood Survey conducted in 1999 [1]. This lower prevalence was also noted in two recent hospital-based studies, which identified the LBW prevalence rate of 12.6% in 2010 and 13% in 2014 [6,7]. However, the exact prevalence of LBW in Sudan may be overestimated or underestimated as this is a hospital-based study, and babies delivered at home were not included. Also, this study was conducted in Khartoum State only.
We found that hypertensive disorders have a significant association with LBW. The risk of delivering LBW infants was found to be approximately three times more in mothers with hypertensive disorders, which is consistent with four other studies [8–11]. Maternal age could confound the effect of hypertension since hypertension tends to occur more in older age groups, and old age itself is a reported risk factor for LBW. However, this possible confounding effect of maternal age was controlled through multivariable regression in this study. The impact of hypertension was shown in an earlier study to be due to the reduced placental blood flow, which leads to decreased fetal growth, and increased risk of intra-uterine growth restriction (IUGR) and LBW [12]. The effect of hypertension on birth weight can be managed by proper antenatal care and health education [9].
Maternal age was found significantly associated with LBW in this study. The mean age for mothers delivering LBW infants was lower compared to the control group, and this finding is supported by many studies [11,13,14]. However, other studies reported that older women are at higher risk of delivering LBW infants [15].
We also found that other variables such as parity, gravidity, and DM were statistically insignificant. While nulliparity was found insignificant in some studies [2,16], other studies have found an association between nulliparity and LBW [4,8]. The lack of association between primigravidity and LBW was also reported in a study conducted in Malaysia [2]. In addition, a study conducted in Sudan concluded that DM during pregnancy is not linked to LBW [7].
The findings of this study need to be considered in the context of some limitations. The information in the records was limited, and thus we were only able to test a few of the risk factors, leaving out other factors that may significantly contribute to LBW, especially maternal anemia as it was found to increase the risk of LBW in several studies in Sudan [6,17,18]. Also, this is a hospital-based study, and newborns delivered at home were not included, which may under- or over-estimate the proportion of LBW.
CONCLUSION
We found that the proportion of LBW was 10.8%. Younger maternal age and hypertensive disorders were independent risk factors for LBW. The proportion of LBW can be reduced if hypertension is controlled by providing simple measures like proper antenatal care and health education for pregnant women.
CONFLICT OF INTEREST
The authors declare no conflicts of interest.
FUNDING
None.
ETHICAL APPROVAL
The institutional review board of the Faculty of Medicine, University of Khartoum granted permission for conducting this research before study initiation, and ethical permission was also granted by the Ethics Committee of Omdurman Maternity Hospital and the National Ethical Clearance Committee of Sudan Federal Ministry of Health. This is a retrospective record-based study; permission to access patients’ records was obtained from hospital authorities, ensuring the confidentiality of all participants’ information at all levels.
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