|Year : 2016 | Volume
| Issue : 4 | Page : 185-189
The relationship between maternal body mass index and the birth weight of neonates in North-West Nigeria
Swati Singh, Constance E Shehu, Daniel C Nnadi
Department of Obstetrics and Gynaecology, Usmanu Danfodiyo University Teaching Hospital, PMB 2370, Sokoto, Nigeria
|Date of Web Publication||21-Dec-2016|
Department of Obstetrics and Gynaecology, Usmanu Danfodiyo University Teaching Hospital, PMB 2370, Sokoto
Background: Birth weight (BW) is an important determinant of infant's well-being. Several factors such as mothers' genetic characteristics, sociocultural, demographic, behavioral factors, prepregnancy body mass index (BMI), and gestational weight gain contribute to BW. Objective: This study assesses the association between the maternal BMI at the first visit to the BW of their babies in women attending antenatal care clinic in Usmanu Danfodiyo University Teaching Hospital (UDUTH), Sokoto Nigeria. Methodology: This was a hospital-based longitudinal study conducted at the Obstetrics and Gynaecology Department of UDUTH, Sokoto, between November 01, 2011 and October 30, 2012. Two hundred and five pregnant women with singleton gestation and uncomplicated pregnancies were consecutively recruited during the antenatal booking visit after the second missed menstrual period and before 13 weeks of gestation and followed up to delivery. Relevant sociodemographic data including the BMI and BW of the Neonates were recorded using a structured questionnaire. Data were analyzed using IBM SPSS version 20 Armonk, NY, USA. Results: The ages of the women range from 16 to 44 years with a mean of 27.45 (±5.32) years. The mean BMI at first visit was 25.09 kg/m 2 (6.06), while the mean BW of the babies was 3.07 (0.54) kg. There was a significant correlation between maternal BMI at their first visit to the BW of the neonates (r = 0.607, P < 0.001). This shows that maternal BMI is directly related to the neonatal BW. Conclusion: Our study has shown that there is a significant relationship between the maternal BMI and the BW of the neonates among antenatal attendees at UDUTH, Sokoto. Further expansion of the work is recommended including adjustment for maternal age, gestational weight gain, and ethnicity.
Keywords: Birth weight, maternal body mass index, Nigeria
|How to cite this article:|
Singh S, Shehu CE, Nnadi DC. The relationship between maternal body mass index and the birth weight of neonates in North-West Nigeria. Sahel Med J 2016;19:185-9
|How to cite this URL:|
Singh S, Shehu CE, Nnadi DC. The relationship between maternal body mass index and the birth weight of neonates in North-West Nigeria. Sahel Med J [serial online] 2016 [cited 2020 Feb 17];19:185-9. Available from: http://www.smjonline.org/text.asp?2016/19/4/185/196359
| Introduction|| |
Birth weight (BW) is perhaps the most important and reliable indicator for neonatal and infant survival as well as their physical growth and mental development. It is the first weight of the fetus or newborn obtained after birth, preferably measured within the 1 st h of life before significant postnatal weight loss has occurred.  As a universal indicator, BW can be used to measure the health, nutrition, and socioeconomic status of population.  Several factors such as mothers' genetic characteristics, sociocultural, demographic, behavioral factors, high body mass index (BMI), and gestational weight gain among others contribute to BW.  Young maternal age, low maternal BMI, and poor weight gain in pregnancy are associated with both increased risk of low BW (LBW) and poor infant survival.
A low maternal BMI and suboptimal weight gain during pregnancy are long recognized risk factors for delivery of infants too small for gestational age, LBW as well as to increase the risk of subsequent obesity and hypertension in the offspring.  However, high maternal BMI is also related to adverse neonatal outcomes including preterm delivery, macrosomia, congenital anomalies, neonatal asphyxia, neonatal death, hypoglycemia, and hyperbilirubinemia, increased the requirement for neonatal intensive care, and a longer duration of hospital stay.  In the United States of America, it was found that only 2% of pregnant women have a BMI <18.5 and more than 50% have a BMI >25.  In the developing countries, women generally have a lower BMI than in the developed countries. Thus, the BMI tend to differ across populations. 
To improve the antenatal care and counseling throughout the world, the global safe motherhood initiative was launched in 1987 in Nairobi Kenya. Nutritional intake and the weight gain during pregnancy are the two main modifiable factors that were observed to influence maternal and neonatal outcome. 
The most of the work on the effect of maternal BMI on neonatal BW has been done in developed countries. The anthropometric characteristics of women in the developed world are different from those of the resource-poor nations. This study assesses the effect of maternal early pregnancy BMI and the neonatal BW in women attending antenatal care clinic in a Tertiary Institution in North-Western Nigeria.
| Methodology|| |
The study was carried out at antenatal clinic of the Department of Obstetrics and Gynecology of the Usmanu Danfodiyo University Teaching Hospital (UDUTH), Sokoto. This a Tertiary Health Institution located in North-West Nigeria. The clientele of the hospital come from Sokoto metropolis and the environs as well as the neighboring States of Kebbi, Zamfara, and Niger Republic. The predominant ethnic group is the Hausa/Fulani, but other Nigerian ethnic nationalities such as Ibira, Nupe, Yoruba, and Ibo among others are also present in the state. The hospital is a 600-bed institution located in Sokoto North-Western Nigeria. It acts as a major referral center for high-risk obstetric cases from health institutions located within and outside the environs. The most of the clientele of the hospital belong to the middle- and low- income status.
Study population, sampling technique, and study protocol
This is an observational longitudinal study that involved pregnant women in the first trimester of pregnancy with singleton gestation as confirmed by ultrasound.
The minimum sample size was determined using a statistical formula that is for a mean of a continuous variable (n = Z 2 S 2 /E 2 ) of the BMI of the pregnant mother at a P value of 0.05% and 95% of confidence interval.  Calculated minimum sample size was 114. However to increase the power of the study, the maximum sample size was increased by 80%. Therefore, 205 women with singleton gestation were recruited in this study.
Overall 1556 women were booked for antenatal care at the UDUTH, Sokoto within the study period of 20 weeks. However, 205 women who booked early in their 1 st trimester were consecutively selected from booking clinic for the study and followed up to delivery. The women were counseled and written, or verbal consent was obtained. A structured interviewer-administered questionnaire was filled for all the participants, to obtain information on age, educational status, parity, occupation, ethnic group, gestational age, maternal smoking habits, and cell phone numbers. Resident doctors who had been trained for the purpose of this research administered the questionnaires.
The height and baseline weight were measured for each woman, and BMI (kg/m 2 ) was calculated at booking, and at subsequent visits. The weight was measured using a spring balance with minimal clothing and without footwear after correcting for zero error. The height was also measured with the same machine. The women were categorized into five sub-groups according to their 1 st trimester BMI as follows: Underweight: BMI ≤19.9 kg/m 2 , normal: BMI of 20-24.9 kg/m 2 , overweight: BMI of 25-29.9 kg/m 2 , obese: BMI of 30-34.9 kg/m 2 , and morbidly obese: BMI >35 kg/m 2 . The group with normal BMI (20-24.9 kg/m 2 ) was used as the reference group for the analysis.  The patients were followed up to delivery, and the BW of the babies was recorded. The neonate was weighed immediately after delivery and without clothing using Seca Medical Scales. The women who had a stillbirth, preterm deliveries, and pregnancy complicated by hypertension, diabetes, and multiple pregnancies were excluded from the study. Furthermore, patients with chronic illnesses, or who were chronic alcoholics were also excluded from the study.
The BWs of the neonates were classified as low, normal, and macrosomic babies. LBW and macrosomia by international standards were defined as a weight of <2500 g and >4000 g, respectively. 
The Medical Research and Ethics Committee of the UDUTH, Sokoto reviewed the study protocol and approval for ethical clearance were given.
Data entry and analysis were done using SPSS, version 20 (IBM, Chicago IL, USA) statistical packages for social sciences and correlation analysis were done to test for association between different variables at P < 0.05 at 95% confidence intervals, which was considered as significant.
| Results|| |
Of the 1556 women who were booked for antenatal care during the study period, 205 met the eligibility criteria and were recruited into the study. The patients' ages range from 16 to 44 years with a mean of 27.45 (5.32) years as shown in [Table 1]. The parity distribution of the study subjects was shown in [Table 2]. Their mean BMI were 25.09 kg/m 2 (±6.07), and 17 (8.3%) were underweight, 105 (51.2%) had within normal limits while 83 (40.5%) of the subjects were obese as shown in [Figure 1].
|Figure 1: Distribution of body mass index at booking among the study groups|
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The proportion of subjects with normal, underweight, and overweight did not differ significantly according to the age groups (Chi-square = 7.982, df = 10, P = 0.63).
The Hausa ethnic group constituted 89 (43.4%) of the subjects, and their mean BMI was 24.6 kg/m 2 (4.06), which was significantly lower than those of the Ibo and Yoruba ethnic group, with means of 27.01 kg/m 2 (3.39) and 26.15 kg/m 2 (5.11), respectively, as shown in [Figure 2].
|Figure 2: Distribution of body mass index (kg/m2) among different ethnic groups|
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Among the 205 mothers that delivered 14 (6.8%) had LBW babies (6 males and 8 females), 174 (84.9%) normal BW babies (89 males and 85 females) while 17 (8.3%) were macrosomic babies (9 males and 8 females).
The mean BW of the babies was 3.07 kg (0.54). Male babies of average BW were more 89 (43.4%) than the females of the same BW 85 (41.5%) as shown in [Table 3].
There was significant association found between low maternal first trimester BMI and the delivery of LBW neonates (<2500 g). Furthermore, obese mothers delivered significantly larger neonates compared to mothers of average weight as shown in [Figure 3]. This was found to be statistically significant with correlation analysis r = 0.607, P < 0.001.
| Discussion|| |
The mean BMI of the pregnant women (25.09 kg/m 2 ) suggests a tendency toward overweight. We also demonstrated inter-ethnic variations in BMI, the value being lower in the Hausa/Fulani ethnic groups (24.6 kg/m 2 ) than the Ibos (27.01 kg/m 2 ) and Yoruba (26.15 kg/m 2 ). This may be related to genetic, nutritional habits, and sociocultural differences among the various ethnic groups. Similar finding was noted in studies from Kathmandu, Nepal, and in India. ,,
An important finding in this study is a high rate of obesity (BMI >25 kg/m 2 ) within the 21-30 years age group, where more than 20% (52/250) of the women were obese. This is the active reproductive age group and thus calls for concern. In relation to parity, 38.7% (46/119) of the primigravida were overweight (BMI >25 kg/m 2 ); while in general, 33.2% (83/250) of the study subjects were obese.
The mean BW of the neonates of 3.07 kg (0.54) is within normal limits. Maternal BMI significantly affected neonatal BW. There was a significant association between low 1 st trimester maternal BMI and the delivery of LBW neonates (r = 0.607, P < 0.001). Furthermore, the incidence of LBW neonates (LBW i.e., <2500 g) was higher in underweight subjects than the average weight and the overweight or obese women. Conversely, obese mothers produced larger babies (mean BW = 3290 g) than average sized mothers (mean BW = 3068 g). This was statistically significant (t-test 2.249, P = 0.02, df = 186). These findings are contrary to the Maiduguri study where maternal pregnancy BMI did not significantly contribute to differences in the BW of neonates.  Larsen et al., showed that the frequency of macrosomia increases with a high BMI.  Besides, an obese woman seems more likely to experience a macrosomic baby than a woman of normal weight. Pregnancy in obese women is associated with a high rate of fetal macrosomia, which tends to be not dependent on gestational diabetes. In another study, maternal prepregnancy BMI was found to a strong association with BW of neonates in Asia. 
Additional factors that have been observed to affect neonatal BW include maternal age, parity, and gender. Male newborns have been shown to have higher BW than females.  In the current report, the mean BW for male neonates of 3130 g was slightly higher than the 3100 g for females, while LBW was more frequent in females than in the males.
This study being hospital, especially, based may not be a true reflection of the influence of maternal pregnancy on the newborn BW.
| Conclusion|| |
Maternal BMI may have a relationship with neonatal BW among the study population.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3]