Arch Gynecol Obstet (2011) 284:235–240 DOI 10.1007/s00404-011-1917-7
R E P R O D U CT IV E M E D I CI N E
Changes in prepregnancy body mass index between pregnancies and risk of gestational and type 2 diabetes Valerie E. Whiteman · Muktar H. Aliyu · Euna M. August · Cheri McIntosh · Jingyi Duan · Amina P. Alio · Hamisu M. Salihu
Received: 15 October 2010 / Accepted: 21 April 2011 / Published online: 5 May 2011 © Springer-Verlag 2011
Abstract Introduction We investigated whether changes in interpregnancy body mass index (BMI) inXuence the risk of gestational and type 2 diabetes among a cohort of women with two consecutive live, singleton births of 20–44 weeks gestation (n = 232,272). Methods Logistic regression models were used to examine the risk for development of gestational or type 2 diabetes during the second pregnancy. Mothers with normal weight for both pregnancies (normal-normal) served as the referent group. Results Across all BMI categories, mothers with signiWcant weight gain (i.e., moving from a lower BMI category into a higher category) had an increased risk for the development of diabetes. Mothers who moved from normal prepre-
gnancy weight (BMI = 18.5–24.9 kg/m2) in the Wrst pregnancy to obese prepregnancy weight (BMI ¸ 30.0 kg/m2) in the second pregnancy showed the greatest increment in risk. These mothers exhibited a threefold risk for developing diabetes (OR = 3.21, 95% CI 2.76–3.73). Mothers who maintained their interpregnancy BMI weight category or who moved to a lower BMI category had reduced risk for gestational and type 2 diabetes. The risk associated with mothers who moved to a lower BMI category was approximately half that of the normal-normal BMI category. Conclusion Interpregnancy weight gain is associated with a dose–response increase in risk of diabetes. Establishing a normal interpregnancy BMI may reduce the risk of diabetes. Keywords Singletons
V. E. Whiteman · H. M. Salihu Department of Obstetrics and Gynecology, College of Medicine, University of South Florida, Tampa, FL, USA M. H. Aliyu Department of Preventive Medicine and Institute for Global Health, Vanderbilt University, Nashville, TN, USA E. M. August Department of Community and Family Health, College of Public Health, University of South Florida, Tampa, FL, USA C. McIntosh · J. Duan · H. M. Salihu (&) Department of Epidemiology and Biostatistics, College of Public Health, University of South Florida, 13201 Bruce B. Downs, MDC56, Tampa, FL 33612, USA e-mail:
[email protected] A. P. Alio Department of Community and Preventive Medicine, University of Rochester, Rochester, USA
Diabetes · Interpregnancy weight gain ·
Introduction The epidemic of obesity aVects women of all ages, with women of reproductive age being particularly aVected. The prevalence of prepregnancy obesity in the United States has increased by at least 70% over a ten-year period [1]. Diabetes is a major complication of obesity in pregnancy [2–5]. Gestational diabetes is associated with increased maternal and neonatal risks and aVects 1–14% of pregnancies in the United States [6]. Type 2 diabetes may result from gestational diabetes and lead to complications for future pregnancies [6]. Diabetes is an important contributor to maternal–fetal morbidity and mortality. Understanding its link to the current obesity epidemic among pregnant women could enhance our ability to institute appropriate and eVective prevention strategies to improve maternal–fetal outcomes.
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Previous studies have demonstrated that prepregnancy weight gain increases the risk of gestational diabetes [7, 8]. In addition, weight gain between pregnancies has been associated with an increased risk for gestational diabetes [9]. Villamor et al. [9] demonstrated that women with a BMI change greater than 3 units were approximately two times more likely to develop preeclampsia or gestational diabetes. However, weight categories for participants in the study were limited to a BMI less than 25 and 25 or greater. In addition, all the possible interpregnancy BMI changes that could occur between pregnancies (e.g., normal-toobese, obese-to-normal, etc.) were not examined. Using a large population-based database we undertake this study with the following aims: (1) to determine whether changes in interpregnancy BMI change impact the risk of diabetes (Type 2 and gestational diabetes) and (2) to investigate if there is a dose-dependent relationship between changes in maternal interpregnancy weight and the outcome of interest.
Methods and procedures The data utilized in this study are from the Missouri maternally linked cohort data Wle and covered the period from 1989 to 2005. Maternal health data were longitudinally linked to birth and fetal and infant death data with the use of unique identiWers. The methods and algorithm used to link the data and validation of the linkage have been detailed previously [10]. The Missouri vital record system is considered a gold standard in validation of national data sets involving matching and linking procedures [11]. The cohort used for this retrospective analysis consisted of women with two consecutive live, singleton births ranging from 20 to 44 weeks gestation (n = 232,272). Maternal body mass index (BMI) was deWned as weight in kilograms divided by height in squared meters (kg/m2). Height was derived from that recorded at the Wrst prenatal visit and prepregnancy weight as reported by the mother at the Wrst visit of each pregnancy [12]. BMI categories were based on the following Institute of Medicine (IOM) guidelines: <18.5 kg/m2 (underweight), 18.5–24.9 kg/m2 (normal weight), 25–29.9 kg/m2 (overweight), and ¸30.0 kg/m2 (obese) [13, 14]. Maternal interpregnancy weight change was deWned using BMI categories for each of the Wrst and second prepregnancy weight groups. As an example, if the woman was obese in both pregnancies, she will be designated as obese-obese. All possible permutations of the weight change groups were used in the analysis (i.e., obese-obese, obese-overweight, obesenormal weight, and obese-underweight, etc.). Normalnormal maternal interpregnancy BMI weights served as referent.
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The main outcome of interest was development of diabetes (gestational diabetes or type 2 diabetes) during the second pregnancy. The following maternal socio-demographic variables were assessed and compared at the baseline of the second pregnancy for each BMI category: maternal age (20–24, 25–30, 30–35 or >35 years), education (<12 years and 12 years or more), marital status (married or unmarried), smoking and alcohol use during pregnancy (yes or no), adequacy of prenatal care (inadequate or adequate), previous BMI and the interval between Wrst and second pregnancy lasting at least 20 weeks. Interpregnancy interval was calculated as the interval between birth of the Wrst and second child minus the gestational age of the second child. It was grouped as Wrst (<1.1 years), second (1.1–1.9 years), third (1.9–3.1 years) and fourth (>3.1 years) quartiles [15]. Adequacy of prenatal care was assessed by use of the revised graduated index algorithm to describe the level of prenatal care utilization among high risk [16, 17]. The index assesses the adequacy of care based on the trimester of prenatal care initiation, the number of visits and the gestational age of the infant at birth. Inadequate prenatal care utilization refers to women who had missing prenatal care information, those who had prenatal care, but at a suboptimal level, or those who had no prenatal care at all. Statistics The 2 test was used to assess diVerences in maternal sociodemographic characteristics and complications across BMI categories. We performed crude frequency comparisons for common maternal obstetric complications (preeclampsia, eclampsia, chronic hypertension, placenta abruption, placenta previa, diabetes and anemia). Logistic regression models were used to examine the risk for diabetes, in relation to changes in maternal interpregnancy BMI categories. The Wnal model included the following covariates: maternal age, race, education, marital status, smoking and drinking during pregnancy, prenatal care, interpregnancy interval, Wrst pregnancy BMI and Wrst pregnancy diabetes. Maintenance of normal BMI between the Wrst and second pregnancies (normal-normal) was set as the referent category. All tests of hypothesis were two-tailed with a type 1 error rate set at 5%. Statistical analysis was performed using SAS version 9.2 (SAS Institute, Cary, NC). The study was approved by the Institutional Review Board at the University of South Florida.
Results There were a total of 670,717 singleton live births from 1989 to 2005 that were available for inclusion in this study. Of these, 108,410 (16.2%) were excluded, as they were not
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Table 1 Comparison of maternal sociodemographic characteristics in the second pregnancy across levels of body mass index (BMI), Missouri, United States (1989–2005) Characteristics
Normal weight
Underweight
Overweight
Obese
(n = 124,934)
(n = 15,794)
(n = 49,461)
(n = 42,083)
Maternal age (years)
<.0001
<20
10,132 (8.1)
2,233 (14.1)
3,633 (7.4)
2,145 (5.1)
20–24
35,754 (28.6)
6,445 (40.8)
15,416 (31.2)
13,926 (33.1)
25–39
37,467 (30.0)
3,974 (25.2)
14,974 (30.3)
13,754 (32.7)
30–34
30,987 (24.8)
2,451 (15.5)
11,266 (22.8)
8,909 (21.2)
¸35
10,594 (8.5)
691 (4.4)
4,172 (8.4)
3,349 (8.0)
Race
<.0001
White
109,666 (87.8)
13,721 (86.9)
41,948 (84.8)
35,032 (83.3)
Black
12,652 (10.1)
1,566 (9.9)
6,776 (13.7)
6,632 (15.8)
Other
2,616 (2.1)
507 (3.2)
737 (1.5)
419 (1.0)
<12
17,712 (14.2)
4,123 (26.1)
6,940 (14.0)
5,7017 (13.6)
¸12
106,653 (85.4)
11,575 (73.3)
42,312 (85.6)
36,201 (86.0)
Education (years)
Not stated
<.0001
569 (0.5)
96 (0.6)
209 (0.4)
165 (0.4)
Marital status
<.0001
Married
96,079 (76.9)
10,361 (65.6)
37,283 (75.4)
30,793 (73.2)
Not married
28,786 (23.0)
5,422 (34.3)
12,162 (24.60
11,274 (26.8)
Not stated
69 (0.1)
11 (0.1)
16 (0.0)
16 (0.0)
Smoking status Smoker Nonsmoker Not stated
<.0001 20,899 (16.7)
4,742 (30.0)
8,130 (16.4)
7,159 (17.0)
103,918 (83.2)
11,041 (69.9)
41,309 (83.5)
34,880 (82.9)
117 (0.1)
11 (0.1)
22 (0.0)
44 (0.1)
Yes
1,329 (1.1)
148 (0.9)
373 (0.8)
214 (0.5)
No
123,472 (98.8)
Alcohol use
Not stated
P
<.0001
133 (0.1)
15,626 (98.9) 20 (0.1)
49,058 (99.2) 30 (0.1)
41,825 (99.4) 44 (0.1)
Prenatal care
<.0001
Adequate
67,903 (54.4)
7,809 (94.4)
27,417 (55.4)
23,741 (56.4)
Inadequate
57,031 (45.7)
7,985 (50.6)
22,044 (44.60)
18,342 (43.6)
the Wrst two consecutive singleton live births for a particular mother. We excluded the following additional records: 31,025 (5.5%) with gestations before 20 weeks or beyond 44 weeks and 44,758 (8.4%) with non-sibling pairs or those with missing or implausible values. Any mothers with insulin-dependent diabetes mellitus [3,457 (0.7%)] were removed from sample. Furthermore, any mothers who had non-insulin-dependent diabetes or preeclampsia in the Wrst pregnancy [18,523 (7.7%)] were excluded for a total of 232,272 pairs of consecutive singleton live births remaining in the analysis. Table 1 summarizes the frequency of select socio-demographic characteristics in relation to maternal BMI categories. In comparison to mothers in the underweight, overweight and obese BMI category at the start of the second pregnancy, normal BMI mothers tended to be
younger, White women, had attained higher education and were more likely to be married. Normal BMI mothers were also less likely to smoke or use alcohol during pregnancy and more likely to receive adequate prenatal care compared to the other weight categories. Mothers of underweight BMI were more likely to have the shortest time-span between pregnancies. Table 2 shows adjusted estimates for the occurrence of diabetes for each BMI category. Overweight and obese mothers had a higher occurrence of diabetes than normal and underweight mothers. Further, increases in BMI resulted in increased risk for diabetes. Compared to mothers within the normal BMI category at the start of the second pregnancy, overweight mothers had an almost two times increased risk of developing diabetes (OR = 1.9, 95% CI 1.7–2.0). Similarly, the risk of disease was over three times
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Table 2 Occurrence of diabetes by BMI status in the second pregnancy, Missouri, United States (1989–2005) Second pregnancy
Underweight Normal
Diabetes
Diabetesa
N = 4,897 (%)
AOR (95% CI)
120 (0.8) 1,466 (1.2)
Table 3 Association between changes in maternal prepregnancy BMI and diabetes in second pregnancy, Missouri, United States (1989– 2005) First pregnancy
Second pregnancy
Diabetes, no. (%)
Diabetes adjusted odds ratioa (95% CI)
1.0 (reference)
Obese
Obese
1,167 (5.5)
1.09 (0.81–1.46) 1.38 (1.03–1.85)
0.7 (0.5–0.8)
Overweight
1,180 (2.4)
1.9 (1.7–2.0)
Overweight
Obese
520 (3.9)
Obese
1,988 (4.7)
3.1 (2.8–3.4)
Normal weight
Obese
209 (3.8)
3.21 (2.76–3.73)
Underweight
Obese
5 (4.0)
2.03 (0.63–6.55)
AOR adjusted odds ratio a Adjusted for maternal age, maternal race, education, marital status, smoking and drinking during pregnancy, prenatal care, interpregnancy interval, Wrst pregnancy BMI
as great for obese compared to normal weight mothers (OR = 3.1, 95% CI: 2.8–3.4). Underweight mothers had a reduced risk for development of diabetes compared to normal weight mothers [OR = 0.7 (0.5–0.8)]. Table 3 provides adjusted estimates for each category of maternal interpregnancy BMI change. Mothers with normal weight for both pregnancies (normal-normal) were used as the referent group. Across almost all categories, mothers with signiWcant weight gain (i.e., moving from a lower BMI category into a higher category) had an increased risk for the development of diabetes. The only exceptions to this were mothers who transitioned from underweight to normal, overweight or obese weight categories. In particular, mothers who were underweight prior to their Wrst pregnancy but became obese before their second pregnancy had a twofold risk of developing diabetes. However, this Wnding was not statistically signiWcant (OR = 2.03, 95% CI 0.63–6.55). The mothers with the greatest increase in risk of diabetes were those who moved from normal prepregnancy weight in the Wrst pregnancy to obese prepregnancy weight for the second pregnancy. These mothers exhibited a threefold increased risk of developing diabetes (OR = 3.21, 95% CI 2.76–3.73). Conversely, mothers who maintained their BMI weight category from the Wrst to the second pregnancy were at lower risk of developing diabetes. Mothers who experienced prepregnancy weight reduction (obese to overweight, obese to normal weight, and overweight to normal weight, and normal weight to underweight) had reduced risk for diabetes. The risk associated with these mothers was approximately half that of the normal-normal BMI category (Table 3).
Discussion Our study conWrmed earlier reports that obese and overweight women have an increased risk of diabetes and that the risk increases with increasing BMI [3, 4, 8, 18]. The
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Obese
Overweight
78 (3.3)
0.66 (0.46–0.96)
Overweight
Overweight
454 (2.3)
0.79 (0.59–1.07)
Normal weight
Overweight
578 (2.3)
1.86 (1.68–2.05)
Underweight
Overweight
10 (1.9)
0.92 (0.35–2.45)
Obese
Normal weight
6 (1.0)
0.21 (0.09–0.50)
Overweight
Normal weight
67 (1.3)
Normal weight
Normal weight
1,213 (1.2)
Underweight
Normal weight
144 (1.3)
Obese
Underweight
1 (2.3)
0.65 (0.30–1.40)
Overweight
Underweight
0 (0.0)
–
Normal weight
Underweight
33 (0.7)
0.69 (0.48–0.97)
Underweight
Underweight
84 (0.8)
0.42 (0.19–0.92)
0.46 (0.32–0.67) 1.0 (reference) 0.46 (0.32–1.40)
SigniWcant values are given in bold a Adjusted for maternal age, maternal race, education, marital status, smoking and drinking during pregnancy, prenatal care, interpregnancy interval and Wrst pregnancy BMI
main goal of this study was to assess the impact of interconceptional BMI change on subsequent risk of diabetes. As we hypothesized, signiWcant increases in weight between pregnancies elevated the risk of diabetes threefold. Women whose prepregnancy BMI changed from normal to obese between the Wrst and second pregnancies had a threefold increased risk in developing diabetes compared to mothers in the normal weight category for both pregnancies. Women whose BMI category changed from normal to overweight also had an elevated risk of diabetes, but to a lesser extent (OR = 1.82, 95% CI = 1.71–1.94). Interestingly, weight loss between the Wrst and second pregnancies decreased the risk of developing diabetes. This is of particular public health signiWcance because even a moderate decrease in weight between pregnancies could have substantial implications in reducing the risk of various maternal obstetric complications [8, 9]. It is appropriate to discuss the biological basis for our Wndings. Pregnancy is characterized by an adaptive physiologic state of decreased insulin sensitivity necessary for supplying suYcient energy to support fetal development. By the third trimester of normal pregnancy, insulin sensitivity decreases to 50–70% that of prepregnancy values, producing an overall two to threefold rise in mean insulin concentrations over any 24-h period [19–21]. Obesity also
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induces a state of insulin resistance, independent of pregnancy, thereby further exaggerating the normal physiologic process. This marked increase in insulin resistance produces a pathological response, resulting in maternal hyperinsulinemia, hyperglycemia and gestational diabetes mellitus [19–22]. Gestational diabetes in turn could in certain cases progress to postpartum type-2 diabetes [4]. Prior studies have shown that gestational weight gain is associated with postpartum weight changes [23, 24]. In particular, women who gain more weight during pregnancy than the US IOM recommendations also retain more weight postpartum than mothers whose weight gain is compliant with IOM recommendations [24–32]. The extent of this weight retention may vary by prepregnancy BMI status; the heavier the woman, the larger the increment of the mean weight retained [26, 28]. Also at risk of postpartum weight retention are lower income and minority groups (especially Black women) [27, 29, 32]. The median retained weight for Black women is on average three times that of White women [27]. The excess weight gained may also linger beyond the immediate postpartum years; mothers who lost their pregnancy weight gain at 6 months postpartum were more likely to have lower BMI at 10 years follow-up than their peers who had retained weight at 6 months postpartum [33]. Other independent risk factors for weight retention at 1-year postpartum include frequency of exercise, food intake and duration of breastfeeding [26]. Unfortunately, we lack information on weight retention, physical activity, nutrient intake and breastfeeding patterns in our study database and are consequently unable to posit their possible impact on our study results. There are other important limitations of this study that should be noted. The use of maternal self-recall to derive estimates for prepregnancy weight was subject to underreporting [34, 35]. Fattah et al. [35] reported that when BMI was measured digitally, 22% of mothers in early pregnancy were misclassiWed on the basis of self-report; 12% of women who were overweight at their Wrst antenatal visit were classiWed as normal, and 5% who were obese were classiWed as overweight [35]. Therefore, any misclassiWcation arising from underreporting in this study would likely tend toward a lower BMI category and thereby bias our Wndings toward the null. The fact that we do report signiWcant Wndings strengthens the validity of our results. Another limitation is our inability to separately analyze gestational and type 2 diabetes due to the way in which the variables were coded in the data set. Finally, pregnancy care, therapies and many life style factors related to obesity, eating behavior, and physical activity have changed since 1989. The extent to which these changes impact our Wndings is not known. However, it is likely that any cohort eVects arising from these trends would be non-diVerential, i.e., would equally aVect all participants in this study.
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A strength of this study is that it is population-based and, thus, results are minimally aVected by selection biases (e.g., referrals), a source of concern in data derived from individual institutions or health facilities. Other strengths include the large sample size and inclusion of analysis that adjusted for numerous confounding factors. The Wnding of an association between weight gain between pregnancies and the development of diabetes suggests that providers should counsel women in regard to overall weight loss and weight loss between pregnancies. Establishing a normal BMI between pregnancies may reduce the risk of adverse outcomes in future pregnancies. ConXict of interest
None.
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