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ORIGINAL ARTICLE
Year : 2018  |  Volume : 6  |  Issue : 2  |  Page : 37-41

Maternal body mass index and its implication on birth weight: A retrospective study


1 Department of Physiology, University of Nigeria, Enugu State, Nigeria
2 Department of Physiology, Ebonyi State University, Ebonyi State, Nigeria
3 Department of Pharmacology and Toxicology, Nnamdi Azikiwe University, Awka, Anambra State, Nigeria
4 Department of Physiology, College of Medicine, Ambrose Alli University, Ekpoma, Edo State, Nigeria

Date of Web Publication25-Feb-2019

Correspondence Address:
Mrs. Iyare O Cordilia
Department of Physiology, University of Nigeria, Enugu Campus, Enugu State
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/njecp.njecp_15_18

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  Abstract 


Background: Maternal obesity has been found to be associated with increased risk of macrosomia and other birth defects in new born. The aim of the study was to determine the role of body mass index on birth weight. Methods: Antenatal and labour records of 200 women were randomly selected and reviewed. Data including maternal height and weight, last menstrual period, gestational age at booking, parity, highest and lowest maternal blood pressure, sex and weight of their babies were collected. Maternal body mass index (BMI) and other variables collected were compared with the corresponding birth weight of the offspring. Data was analysed by cross tabulation and percentages. Result: The result showed that irrespective of BMI, 90% of the women had normal birth weight babies (2.5-3.5 kg). Conclusion: It was concluded from this study that maternal BMI alone is not an effective marker for the evaluation of birth weight of offspring.

Keywords: Body mass index, macrosomia, parity


How to cite this article:
Cordilia IO, Jacinta ON, Juliet AO, Eghosa IE, Inegbenebor U. Maternal body mass index and its implication on birth weight: A retrospective study. Niger J Exp Clin Biosci 2018;6:37-41

How to cite this URL:
Cordilia IO, Jacinta ON, Juliet AO, Eghosa IE, Inegbenebor U. Maternal body mass index and its implication on birth weight: A retrospective study. Niger J Exp Clin Biosci [serial online] 2018 [cited 2019 Sep 22];6:37-41. Available from: http://www.njecbonline.org/text.asp?2018/6/2/37/252841




  Introduction Top


Maternal nutritional state is important for the health and quality of life of women. Maternal prepregnancy nutritional status and pregnancy weight gain also affect the survival and health of the newborn. Consequently, various recommendations about pregnancy weight gain have been made.[1],[2] A report published in 1990 confirmed a strong association between maternal pregnancy weight gain and birth weight and provided target ranges of recommended weight gain by prepregnancy body mass index (BMI).[3],[4]

BMI provides a reliable indicator of body fatness for most people, and it is used to screen for weight categories that may lead to health problems. BMI, although not a perfect method for weight determination, is often a good way to check on how a child is growing.[5],[6] BMI is defined as an individual weight in kilogram divided by the square of height in meters. Birth weight is a strong indicator for survival, growth, long-term health, and psychological development of a newborn. Variations of average birth weight have been associated with infant gender, multiple birth factors, and maternal factors such as race, and ethnicity, size, nutrition, and previous medical risk characteristics.[7]

Attempts have been made in recent years to identify the association between BMI and birth weight. There is need to recognize this association in our environment since at low and high birth weights, an infant's risk of mortality soars.[8] There is also a need to prevent low birth weight to improve outcome of pregnancy and reduce neonatal mortality rate. It is known that children of uncontrolled diabetic mothers are often macrosomic because of the persistent hyperglycemia in the blood supply to fetus, which the fetal insulin stores in the fetus.[9] However, in nondiabetic mothers, the role played by factors such as maternal height and weight, parity, gestational hypertension, gestational age at booking, and sex of the baby is not quite clear, hence this study.


  Materials and Methods Top


Background to the study population

St. Camillus Hospital, Uromi, is a mission hospital which was established in 1948. It serves as maternity for women of reproductive age in Edo Central Senatorial District, Edo State, Nigeria. Edo Central Senatorial District is composed of five local government areas: Esan Central, Esan North-East, Esan South-East, and Esan West.

Study design

This was a retrospective study of women who booked at the antenatal clinic and delivered their babies in the labor ward of St. Camillus Hospital, Uromi, between April 2006 and December 2010 inclusive.

Study population

A total of 840 women, who delivered in St. Camillus Hospital in Edo Central Senatorial District from April 2006 to December 2010, were used as the study population.

Study sample

  1. 200 randomly selected women who delivered from 2006 to 2010
  2. 200 babies of the randomly selected women.


Method of data collection

A total of 200 randomly selected case files of women who had antenatal clinics and deliveries in St. Camillus hospital, Uromi, were reviewed, and information on maternity weight, height, parity, last menstrual period, blood pressure at booking, highest blood pressure, gestational age at booking, fetal sex, and birth weight was recorded and analyzed.

Inclusion and exclusion criteria

Only women who had singletons were selected. All women who delivered preterm (<37 weeks) and postterm (>40 weeks) were excluded.

Method of data analysis

Data analysis was done using cross-tabulation and percentages.

Duration of the study

This study was carried out between September and November 2010.

Ethical consideration

This study was approved by the Medical Director, St. Camillus Hospital. Since only routinely collected and anonymous data were analyzed, individual's consent was not required. Based on the nature of the research work, individuals were not met in person.


  Results Top


Irrespective of the BMI, most of the women in these categories had normal weight babies [Table 1].
Table 1: Effect of body mass index on birth weight

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29%, 46%, and 25% of the women studied were primiparous, multiparous, and grandmultiparous, respectively [Table 2]. Low birth weight was more common among the primiparous women. Macrosomic babies were more common among the grandmultiparous women. There were lower frequencies of underweight babies (2%) and macrosomic babies (3%) in the multiparous women.
Table 2: Effect of body mass index and parity on birth weight

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The incidence of hypertension among the study group was 2.5% [Table 3]. Overweight women with hypertension had equal incidence of underweight and normal weight babies. Obese hypertensive women were most likely to have underweight babies.
Table 3: Effect of body mass index and hypertension on birth weight

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The ratio of male-to-female births was 102:98 [Table 4]. Male babies were twice more likely to be underweight or overweight. Females were slightly more in the normal weight category though this was not significant.
Table 4: Effect of body mass index and sex on birth weight

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There was no low birth weight among the women who booked in the first trimester [Table 5].
Table 5: Effect of gestational age at booking on birth weight

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Seventy-five percent of the macrosomic babies were born to women who were 70 kg and above [Table 6]. The incidence of underweight babies was lower in underweight and obese women.
Table 6: Effect of maternal weight on birth weight

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Macrosomic babies were more common with taller women [Table 7].
Table 7: Effect of maternal height on birth weight

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  Discussion Top


Birth weight is a major determinant of pregnancy outcome. Birth weight >4.0 kg may be a case of cephalopelvic disproportion, fetopelvic disproportion, shoulder dystocia, and other conditions, which often result in difficult deliveries or surgical intervention.[10],[11] In tropical countries such as Nigeria, the availability of expertise to manage these conditions may be unavailable, scarce, or too expensive for those in need of these services. Hence, there is a need to prevent macrosomia in these areas with dearth of facilities and workforce. The common problems of low birth weight include respiratory distress syndrome.[12]

It is known that children of uncontrolled diabetic mothers are often macrosomic because of the persistent hyperglycemia in the blood supply to the fetus, which the fetal insulin stores in the fetus.[9]

BMI of women who booked at the antenatal clinic was used as a parameter in this study to group women into underweight, normal weight, overweight, and obese. The birth weights of the offspring of these women were noted.

The findings from this study showed that irrespective of BMI, 6% of the women had low birth weight babies while 90% had normal birth weight babies. Macrosomia was found in 4% of the babies. Only 10% of underweight women had underweight babies [Table 1]. This is not surprising since the fetus which is a parasite on the mother must obtain all its nutrients whether or not the mother is adversely affected. 83% of obese women had babies with normal birth weight, while 17% had low birth weight babies. While a fetus can obtain all its nutrients from the mother, additional factors such as diabetes mellitus which allow a lot of sugar to be pumped into the fetal circulation may predispose the fetus to macrosomia. The absence of macrosomia in these nondiabetic obese women reinforces the well-known fact that obesity per se is not responsible for macrosomia. It was surprising that 17% of obese women gave birth to low birth weight babies. This may be due to other confounding variables such as vascular diseases in the mother which may have prevented nutrient flow from mother to child.

All the macrosomic babies in this study (4%) were delivered by normal and overweight women [Table 6]. This may be explained by other factors such as dietary habit of the mother. A woman who indulges in a lot of sugary drinks can stimulate the hyperglycemic environment of the diabetic woman and predispose its fetus to macrosomia. Besides, most underweight women are those who are always eating but are yet to develop vascular complication. It is noteworthy that only 5% of women with normal BMI had low birth weight babies. The findings on BMI indicated that BMI alone might not be responsible for fetal birth weight.[13]

The effect of parity on birth weight was investigated [Table 2]. Findings showed that the highest number of women (12%) in primiparous group had babies with low birth weight compared to their counterparts in multiparous (1%) and grandmultiparous (1.5%) groups. This might explain the fact that primiparous women are inexperienced in the act of proper nutrition during pregnancy. Macrosomic babies were found in multiparous and grandmultiparous mothers but not in primiparous women. This might be an indication that parity predisposes women to macrosomic babies although the mechanism is yet unknown.[14]

Gestational hypertension is another factor that was evaluated [Table 3]. The findings showed that macrosomic babies were only born to normal weight hypertensive mothers but none to underweight, overweight, or obese mothers. This is an indication that irrespective of BMI, gestational hypertension might be a predisposing factor to having macrosomic babies. Underweight babies were born to normotensive and hypertensive overweight and obese mothers. This could be as a result of placenta pathology associated with vasculopathy as result of obesity.[15]

The sex of the baby was also investigated in this study. The result showed that the ratio of male-to-female babies in this study was 102:98 [Table 4]. The findings show that more males (5) to females (3) were born overweight and underweight (8:3). There is no significant difference in the number of males to females born with normal weight. It is interesting to note that no overweight baby of either sex was born to obese mother. Only 4 (33%) of underweight males were born to obese mothers. These findings showed that irrespective of BMI, more males than females are likely to be born macrosomic, hence indicating that baby sex might play a role in having a macrosomic baby. This is in line with a study where male fetal sex was highlighted among others as a risk factor for macrosomia.[16]

Gestational age at booking was another important factor that was evaluated, and according to the data collected, only 5% of women booked in their first trimester [Table 5]. This is consistent with findings by several authors who have noted that most Nigerian women book late at the antenatal clinic.[17],[18] The findings on this factor showed that women who booked in their first trimester had few or no macrosomic babies with no underweight baby. Macrosomic babies were more in women who booked in their second and third trimester. This is an indication that gestational age at booking might have an effect on birth weight.

Maternal weight might also be a contributing factor. According to the findings of this study, 75% of the macrosomic babies were delivered by women who were 70 kg and above [Table 6]. This suggests that overweight women are more likely to give birth to macrosomic babies. This is in consonance with a finding where macrosomic rate was significantly higher (24.6%) for overweight women than nonoverweight women (10.4%).[19] However, this is more likely to occur in the absence of vascular diseases such as hypertension.

Data collected and analyzed on maternal height revealed that macrosomic babies were more common among the taller women above 1.69 m [Table 7]. Although BMI is inversely proportional to height, most tall women are likely to have high body mass, hence annihilating the inverse effect of height.[20]

Limitation

BMI was calculated with weight of the pregnant woman at booking. Therefore, weight of the product of concentration, slight addition to the weight of the mother, led to slightly erroneous results of BMI. The women booked at different gestational ages and so the additional weight of product of conception was not uniform in all mothers.


  Conclusion Top


Birth weight is not necessarily a function of BMI in nondiabetic women. Other variables such as hypertension, parity, time of booking, baby sex, and maternal weight are also implicated in high birth weight. Hence, there is need to sensitize expecting mothers on the impact of these factors in high birth weight so as to improve the health and survival of newborn.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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Rich-Edwards JW, Colditz GA, Stampfer MJ. Birthweight and the risk for type 2 diabetes mellitus in adult women. Ann Intern Med 1999;130:278-84.  Back to cited text no. 9
    
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Revicky V, Mukhopadhyay S, Morris EP, Nieto JJ. Can we predict shoulder dystocia? Arch Gynecol Obstet 2012;285:291-5.  Back to cited text no. 11
    
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Ferraro ZM, Barrowman N, Prud'homme D, Walker M, Wen SW, Rodger M, et al. Excessive gestational weight gain predicts large for gestational age neonates independent of maternal body mass index. J Matern Fetal Neonatal Med 2012;25:538-42.  Back to cited text no. 13
    
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Nkwabong E, Nzalli Tangho GR. Risk factors for macrosomia. J Obstet Gynaecol India 2015;65:226-9.  Back to cited text no. 14
    
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Thorne J, Downey P, Mooney EE. Placental pathology associated with small for gestational age infants. Ir Med J 2014;107:249-50.  Back to cited text no. 15
    
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Koyanagi A, Zhang J, Dagvadorj A, Hirayama F, Shibuya K, Souza JP, et al. Macrosomia in 23 developing countries: An analysis of a multicountry, facility-based, cross-sectional survey. Lancet 2013;381:476-83.  Back to cited text no. 16
    
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Siega-Riz AM, Viswanathan M, Moos MK, Deierlein A, Mumford S, Knaack J, et al. Asystematic review of outcomes of maternal weight gain according to the institute of medicine recommendations: Birthweight, fetal growth, and postpartum weight retention. Am J Obstet Gynecol 2009;201:339.e1-14.  Back to cited text no. 19
    
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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]



 

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