Association Between Parity, Live Birth and the Risk of Obesity in Women

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Article Information:


Group: 2007
Subgroup: Volume 5, Issue 4, Autumn
Date: December 2007
Type: Original Article
Start Page: 109
End Page: 118

Authors:

  • KO Hajian-Tilaki
  • Department of Social Medicine and Health, Babol, I.R.Iran
  • B Hiedari
  • Department of Internal Medicine, Shaheed Beheshti Hospital, Babol University of Medical Sciences, Babol, I.R.Iran

      Correspondence:

      Affiliation: Department of Social Medicine and Health
      City, Province: Babol,
      Country: I.R.Iran
      Tel:
      Fax:
      E-mail: drhajian@yahoo.com

Abstract:


Obesity is a rapidly increasing concern among women and men particularly in the Middle East countries. This study was aimed to determine the relation between reproductive factors and the risk of obesity, particularly abdominal obe-sity in women. Materials and Methods: We conducted a popula-tion based cross-sectional study on a sample of 1800 women, aged between 20 to 70 years, using cluster sampling techniques in an urban area, in the north of Iran. The height, weight and waist circumference were measured with standard methods and information on the number of pari-ties, live births, pregnancy, social and demo-graphic status, and data on life style was col-lected during interviews. Results: The mean (±SD) age of women was 37.5±13.0 years; 22.6% of women were nullipa-rous, 31.7% had 1-2, and 19.9% ≥5 pregnancies respectively. About 22.9% of women had no his-tory of parity, and33.8%, and 17.4% had 1-2 and ≥5 parities respectively. The overall prevalence rate of obesity and abdominal obesity was 27.7% and 46.2% respectively. In multiple logistic re-gression analysis, after adjustment for age, edu-cation level, marital status, parental obesity, marriage age, occupational activity, leisure time physical activity, duration of exercise per week, the risk of obesity increased significantly by 9% (adjusted OR=1.09, 95%CI: 1.01-1.18) and 10% (adjusted OR=1.10, 95% CI: 1.01-1.21) with each additional parity and live birth respectively. Conclusion: The results of this study indicate that the risk of obesity escalates with increase in the number of parities and live births. Hence, reproductive factors should be considered as in-dependent risk factors of obesity in women.

Keywords: Obesity;Central obesity;Parity;Number of live births;Sociodemographic status

Manuscript Body:


Introduction

Obesity is a rapidly increasing health problem wordwide, with overall rates of obesity rising dramatically in recent decades.1-6 It has serious effects on the development and evolution of type 2 diabetes, hypertension, osteoarthritis and cardiovascular diseases and mortality from cardiovascular diseases rises with increases in body mass index (BMI), beyond the normal range.7-9

Obesity increases metabolic risk and induces motor dysfunction in obese females; and excessive abdominal fat distribution appears to be a significant factor in increasing cardiovascular disease risk among obese women.9,10

Increasing BMI among women in the United States gives rise to concerns about associated comorbid conditions and decreases in life expectancy.11 In the Iranian population, the prevalence of obesity, overweight, and hypertension are as high as in the US; however, Iranian women are more obese than American women12 Furthermore, in the Iranian population, obesity, central obesity (abdominal obesity) and metabolic syndrome are more frequent in women than in men.8,13

Recent increases in the prevalence of obesity worldwide are believed to be caused largely by an environment that encourages sedentary lifestyles and excessive food intake.14 It is likely that a gene-environment interaction, in which genetically susceptible individuals respond to an environment with increased availability of palatable energy-dense foods and reduced opportunities for energy expenditure, contributes to the current high prevalence of obesity.9

In addition to genetic factors and changing life styles as factors of obesity, reproductive factors are also contributing factors of obesity in women, both in developed and developing countries.15-19

Socio-demographic and behavioral variables have been shown to modify the relationship between parity and body weight.17,19,20 The relationship between parity and obesity was however found to be independent of other factors such as geographical area, region, marital status, occupation, smoking habits, and educational levels.11,18,20-22

However, the impact of factors such as low educational level, low socioeconomic status, low physical activity as proposed potential confounding factors in the parity-obesity relationship cannot be ignored, since in many geographic regions, particularly in developing countries, these factors have been documented as causes of both obesity and central obesity in women.1, 23, 24 The effects of reproductive factors such as parity and live births on body weight vary by race, size of place of residence and education.16,25 The importance of parity as a predictor of overweight increases with national economic development and wealth.23 Understanding the role of reproductive factors in the development of weight gain can help improve present strategies for prevention of obesity and central obesity during child bearing years and afterwards.Despite several studies in association with risk factors of obesity, not too many investigations have examined the relation between obesity and reproductive factors.15,16,19-21,26,27 However, the samples of these studies were not homogeneous regarding race, place of residence, age, education, smoking habit, physical activities and other socio-demographic and behavioral factors. Hence, the results of these studies are applicable to a limited population, and cannot be generalized to populations with different socio-demographic or ethnic characteristics. To investigate the independent effect of reproductive factors on the risk of obesity and abdominal obesity, and to minimize the confounding effects of other obesity associated factors, the present study was carried out in a uniform population of women aged 20-70 years in the north of Iran, which is relatively homogenous in lifestyle, race, cultural, and religious beliefs, occupation, physical activity and eating habits as well as behavioral factors.

Materials and Methods

Study subjects and sampling techniques: in 2004 we conducted a cross-sectional population based study in urban areas of four major cities in Mazandardan, a province north of Iran,. A total of 1800 women, aged 20 to 70 years, with no chronic or acute systemic or known debilitating diseases who were resident of the geographic regions of the selected clusters, entered the study.

Pregnant women and those on weight losing diets programs were excluded. A cluster sampling technique was applied using 30 clusters for each city. Initially for cluster selection, in each city, the centers of 30 clusters were chosen randomly using systematic sampling based on cumulative frequency of family health numbers under coverage of urban health centers. Then, around the center of each cluster, 15 women aged 20 to 70 were selected with rotation from the right to the  left  of each cluster center. Written informed consent was obtained from all subjects prior to their participation in the study.

Data collection and measurements: We performed an indoor household survey. Anthropometric measurements of weight, height and waist circumference (WC) were measured using standard methods. WC was measured on waist diameter at the level midway between the iliac crest and lower border of the tenth rib. BMI was calculated by weight in kilograms divided by height in meters squared (kg/m2).

A structured questionnaire was designed and data were collected, during interviews, on demographic and social characteristics such as age, marital status, age at marriage, educational level, occupational activity, history of parental obesity defined as obesity in one or both parents (obesity in parents was determined by observers if the parents were alive, otherwise the history of  parental obesity was reported by the offsprings based on their comparison with other members of the family), levels of physical activity, leisure time activity and the duration of exercise per week by hour (h/w), the number of  parities, and live births.

Occupational activity was categorized in to three groups, low, moderate and vigorous, based on severity of physical activity during working hours. Leisure time physical activity was also categorized into four groups based on the duration of regular exercise activity, and the duration of walking/jogging activity performed weekly; (very low: Less than 20 minutes waking per day without any exercise; low: 20-39 minutes waking per day or mild exercise with duration less than 20 minutes per day; high: 40-59 minutes waking per day or moderate exercise of 20-29 minutes per day; very high: severe waking/jogging >60 minutes per day or continuous and regular exercise over 30 minutes per day.  Parity was defined as the number of live births plus still births with gestational age of >20 weeks. Marital status was defined  as single  (unmar-

 

ried) or married (divorced and widows were included for analysis in the married group). We used standard recommended WHO criteria, BMI= or >30 kg/m2 to define obesity and BMI of 25-29 kg/m2 as overweight. Diagnosis of abdominal obesity was based on the cut-off value of WC>88 cm.

Statistical analysis: SPSS software version 12.0 was used for statistical analysis. First, we used univariate analysis using Chi square test for trend, to describe the prevalence of both obesity and abdominal obesity in relation to parity and the number of live birth and to estimate the crude value of odds ratio of parity on risk of obesity and abdominal obesity. Then, multiple logistic regression model was applied to estimate the adjusted odds ratio of reproductive  factors on both obesity and abdominal obesity by controlling other potential confounding factors such as age, marital status, age at marriage, parental obesity, educational level, occupational activity, and leisure time physical activity, and the duration of exercise per week by hour. The 95% confidence interval of odds ratio was calculated. For likelihood ratio, Chi square test was used and P value below 5% was considered significant.

Results

The mean±SD age of the study subjects was 37.5 ±13.0 years, and 83.9% of participants were married. The mean±SD age of married women was 19.2±3.8 years; in 55.8% of women, age at marriage was below 20 years. The first quartiles, median and third quartile of parity among married women were 2, 3 and 4 respectively, and the corresponding values for number of live births were 1, 2 and 4 respectively. Approximately 407 subjects (22.6%) had no history of pregnancy; 570 (31.7%) had 1-2 pregnancies, and 358 subjects (19.9%) had >5 pregnancies. Characteristics of the study subjects in relation to obesity status are presented in Table 1.

Table 1. Distribution of demographic characteristics, life style related factors, parity and live birth in obese and non-obese women

Characteristics Obese
n (%)
Non-obese
n (%)
Total
n (%)
P value
Age (years)




     
 20-29
74 (14.8) 534 (41.1)
 608 (33.8)
 
 30-39 123 (24.6) 323 (24.9) 446 (24.8)
 <0.001
 40-49 154 (30.9) 218 (16.8) 372 (20.7)
 
 50-59 103 (20.6) 151 (11.6) 254 (14.1)
 
 60-70 45 (9.0) 73 (5.6) 118 (6.6)
 
Education
 




     

 Illiterate

87 (17.4)  140 (10.8)
227 (12.6)
 
 Primary level
147 (29.5)
190 (14.6)
337 (18.7)
 
 Elementary level
106 (21.2)
220 (16.9)
326 (18.1)
<0.001
 High school and college
134 (26.9)
520 (40.0)
654 (36.4)
 
 University level
25 (5.0)
229 (17.6)
254 (14.1)  
Marital status

 
     
 Single
22 (4.4)
265 (20.4)
287 (16.0)
 <0.001
 Married
477 (95.6)
1034 (79.6)
1511 (84.0)
 
Parental obesity
       
 Absent
245 (49.1)
870 (67.0)
1115 (62.0)
 <0.001
 Present
254 (50.9)
428 (33.0)
682 (38.0)
 
Exercise (hr/week)
       
 None
343 (69.7)
828 (64.3)
1171 (65.8)
 
 1-2 h
95 (19.3)
271 (21.0)
366 (20.6)
 0.019
 3-4 h 24 (4.9)
116 (9.0)
140 (7.9)
 
 G5 h
30 (6.1)
73 (5.7)
103 (5.8)
 
Occupational activity
       
 Low
341 (68.3)
900 (69.3)
1241 (69.0)   
 Moderate 153 (30.7)
375 (28.9)
528 (29.4)
 0.36
 High
5 (1.0) 24 (1.8)
 29 (1.6)  
Leisure time physical activity
       
Very low
317 (63.5)
782 (60.2)
1099 (61.1)
 
Low
106 (21.2)
329 (25.3)
435 (24.2)
 0.34
High
61 (12.2)
150 (11.5)
211 (11.7)
 
Very high
15 (3.0)
38 (2.9)
53 (2.9)
 
Parity
       
 None 41 (8.2)
 369 (28.5)
410 (22.8)
 
 1-2
133 (26.7)
475 (36.6)
608 (33.9)
 <0.001
 3-4 189 (38.0)
275 (21.2)
464 (25.8)
 
 G5 135 (27.1)
178 (13.7)
313 (17.4)
 
No. of live births
       
 None 42 (8.4)
377 (29.0)
419 (23.3)
 
 1-2 142 (28.5) 488 (37.6) 630 (35.0) <0.001
 3-4 197 (39.5) 286 (22.0) 483 (26.9)  
 G5
118 (23.6)
148 (11.4)
266 (14.8)
 

 

Overall, 227 participants (12.6%) were illiterate, and 254 (14.1%) subjects had university level education. With regard to parity, 410 participants (22.8%) were nulliparous, 608 (33.9%) had 1-2 and 464(25.8%) had 3-4, and 313 (17.4%) participants had ≥ 5 parities. With respect to the number of live births, 419 (23.3%) participants had none, 630 (35%) subjects had 1-2, 483 (26.9%) had 3-4, and 266 participants (14.8%) had > 5 children. In terms of physical activity, 1171 participants (65.8%) had no exercise and/or sport activity, 103 (5.8%) had exercise activity at the level of 5 hours or more per week, whereas, the levels of activity in the remainder of the study population were between 1- 4 hours per week. Low occupational activity was reported by 1241 (69%) subjects and low or very low leisure time physical activity was reported by 85.5% of subjects.Prevalence rates of obesity and abdominal obesity in relation to parity and number of live birth are summarized in Table 2. The overall rates of obesity and abdominal obesity were 27.7% and 46.2% respectively. The prevalence rate of obesity as well as abdominal obesity has also risen with a significant trend of a dose response relationship by increasing the number of parities and live births (from 10% in nulliparous women to 43.1% in multiparous women with 5 or more live births (Table 2).

Table 2. Prevalence of obesity and abdominal obesity with respect to parity and number of live births
in women

Reproductive factors Obese†
n (%)
Non-obese
n (%)
Abdominally obese‡
n (%)
Not abdominally obese
n(%)
Parity        
 none
 41 (10.0)
369 (90.0) 102 (24.8)
310 (75.2)
 1-2 133 (21.9)
475 (78.1)
225 (37.0)
383 (63.0)
 3-4 189 (40.7)
275 (59.3)
286 (61.6)
178 (38.4)
 G 5 135 (43.1)
178 (56.9)
217 (69.3)
96 (30.7)
 Total 498 (27.7)
1297 (72.3)
830 (46.2)
967 (53.8)
 Live births
       
none
42 (10.0)
377 (90.0)
106 (25.2)
315 (74.8)
1-2
142 (22.5)
488 (77.5)
236 (37.5) 394 (62.5)
3-4
197 (40.8)
286 (59.2)
307 (63.6)
176 (36.4)
G 5
118 (44.4)
148 (55.9)
182 (68.4)
84 (31.6)
Total
499 (27.8) 1299 (72.2)
831 (46.2)
969 (53.8)

†Obesity was defined as BMI

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