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doi:10.1111/jog.12353
J. Obstet. Gynaecol. Res. Vol. 40, No. 5: 1296–1303, May 2014
Associations between the pre-pregnancy body mass index and gestational weight gain with pregnancy outcomes in Japanese women Tomohito Tanaka1,2, Keisuke Ashihara1, Michihiko Nakamura1, Takayoshi Kanda1, Daisuke Fujita2, Yoshiki Yamashita2, Yoshito Terai2, Hideki Kamegai2 and Masahide Ohmichi2 1
Department of Obstetrics and Gynecology, National Hospital Organization Osaka Minami Medical Center, Kawachinagano, and 2Osaka Medical College, Takatsuki, Japan
Abstract Aim: To examine the associations between the pre-pregnancy body mass index (BMI) and gestational weight gain (GWG) with pregnancy outcomes in Japanese women. Methods: The medical records of 1883 Japanese women who delivered singleton infants from January 2010 to January 2013 at Osaka-Minami Medical Center were retrospectively reviewed. We use the BMI classification which the World Health Organization defined for Asian populations and the GWG classified based on the current 2009 Institute of Medicine (IOM) recommendations. The odds ratio (OR) of each of the groups for the different pregnancy outcomes were compared to the recommended group using a logistic regression analysis adjusted by age, gestational weeks, parity, weight gain, mode of delivery, pregnancy induced hypertension (PIH) and gestational diabetes mellitus. Results: Women who were obese (BMI, ≥25 kg/m2) and overweight (BMI, 23–24.9 kg/m2) had a higher rate of developing PIH (adjusted OR, 6.68 and 3.21 [95% confidence interval [CI], 3.31–13.3 and 1.29–7.24]). In contrast, GWG exhibited a correlation with the weight of the infant. The inadequate GWG group had a higher rate of small-for-gestational age (SGA) infants (adjusted OR, 1.72 [95% CI, 1.22–2.46]). The rate of emergency cesarean section was not significantly different between the groups. Conclusion: A pre-pregnancy BMI less than 23 kg/m2 is desirable to prevent Japanese women from developing PIH. GWG within the IOM recommendations also reduced the risk of PIH and SGA. Key words: body mass index, Institute of Medicine, Japanese, pregnancy outcome, weight gain.
Introduction The recommendations for gestational weight gain (GWG) have been highly controversial in the world. In 1990, a report from the Institution of Medicine (IOM) confirmed a strong association between the GWG and infant size and provided target ranges of recommended weight gains based on the pre-pregnancy
body mass index (BMI).1 In 2009, the IOM reexamined the guidelines for GWG issued in 19902 using the BMI classification developed by the World Health Organization (WHO) and adopted by the National Heart, Lung and Blood Institution.3 In Japan, women have become slimmer year by year. More than 20% of Japanese women in their 20s are underweight, a percentage much higher than that in
Received: September 19 2012. Accepted: October 31 2013. Reprint request to: Dr Tomohito Tanaka, Department of Obstetrics and Gynecology, Osaka Medical College, 2-7 Daigaku-machi, Takatsuki, Osaka 569-8686, Japan. Email: [email protected]
1296
© 2014 The Authors Journal of Obstetrics and Gynaecology Research © 2014 Japan Society of Obstetrics and Gynecology
Pre-pregnant BMI and GWG
most developed countries.4,5 As for obesity, which the WHO has defined as a BMI over 30 kg/m2, the prevalence of obesity in Japan is no more than 2–3%, in contrast to the 10–20% observed in Europe and the USA. Although the prevalence of obesity (BMI, ≥30 kg/ m2) has changed little over the past 40 years in Japan, the incidence of obesity-related chronic diseases, such as diabetes, hypertension and hyperlipidemia, has increased.6 Thus, obesity defined by the WHO may not apply to Asian women. Some authors have suggested the use of a modified BMI classification, and the WHO has defined a BMI classification for Asian populations.6,7 This classification proposes a criteria for obesity of a BMI over 25 kg/m2 and that for an overweight status of a BMI between 23 and 25 kg/m2 for people from the Asia–Oceania region, because data have shown that the incidence of obesity-related diseases significantly increases in subjects with a BMI of 23 kg/m2 or more. However, the appropriate level of GWG in Asian women, including Japanese women, remains controversial. We retrospectively examined the associations between the pre-pregnancy BMI and the GWG with the pregnancy outcomes in Japanese women. This study is based on the IOM recommendations for the Asian population, after changing the thresholds for being overweight and obesity.
Methods After obtaining institutional review board approval, the medical records of Japanese women who delivered at Osaka-Minami Medical Center in Kawachinagano Japan between January 2010 to January 2013 were retrospectively reviewed. The aim of this study was to examine the odds ratio (OR) of each group for pregnancy outcomes compared to the recommended group using the WHO classification7 and IOM guidelines.2 A total of 1883 pregnant women were enrolled in this
study. The hospital is not a tertiary facility. All of the women were delivered between 35 and 42 weeks of gestation, and women with multiple gestation, underlying diseases or complications and those with preterm birth do not deliver at our hospital. Therefore, the women enrolled in this study comprised a low-risk population. The women who were not Japanese were also excluded. Each subject reported her prepregnancy weight at the first medical examination. The height and end of pregnancy weight were measured at admission for delivery. The pre-pregnancy BMI and GWG were calculated by these values. The gestational age was estimated from the last menstrual period, which was confirmed or corrected by ultrasound examinations. All the women were categorized according to the WHO classification7 and IOM guidelines;2 for those with a BMI of less than 18.5 kg/m2 (underweight), the total recommended weight gain was between 12.5 and 18 kg; for those with a BMI between 18.5 and 22.9 kg/m2 (normal weight), the total recommended weight gain was between 11.5 and 16 kg; for those with a BMI of between 23 and 24.9 kg/m2 (overweight), the total recommended weight gain was between 7 and 11.5 kg; and for those who had a BMI of 25 kg/m2 or more (obese), the total recommended weight gain was between 5 and 9.1 kg. The women with a GWG within the IOM recommendation were categorized as having an adequate GWG. The women with a GWG less than the IOM recommendation were categorized as having an inadequate GWG. The women with a GWG greater than the IOM recommendation were categorized to have an excessive GWG (Table 1). The incidence rates of pregnancy-related complications, including pregnancy-induced hypertension (PIH), gestational diabetes mellitus (GDM), small-forgestational age (SGA) and large-for-gestational age (LGA) infants were examined in each group. The duration of labor and the rate of post-partum hemorrhage (PPH), emergency cesarean section (ECS), delivery
Table 1 Pre-pregnancy BMI and GWG categories GWG category
Pre-pregnancy BMI category BMI 1000 mL) after delivery. The duration of labor was defined as the length of time from the onset of labor, which was defined as regular and painful uterine contractions, to the delivery of the placenta. The neonatal outcome was evaluated by the rates of a low Apgar score and intrauterine fetal death (IUFD). All of the statistical analysis was performed using the JMP software package (version 9.0.2). The continuous variables were expressed as the means ± standard deviations as determined by an anova. The clinical characteristics and obstetric outcomes of the categorical data or the frequency of an event were analyzed using Fisher’s exact test and the χ2-test with Yates’ correction, respectively. Simple regression analysis was used to examine the associations between pre-pregnancy BMI or GWG and pregnancy events. A multiple logistic regression analysis model was also used to calculate adjusted OR and 95% confidence intervals (CI). Maternal age, parity, length of gestation, mode of delivery, PIH, GDM and GWG were considered to be confounding factors. The models were adjusted for these factors in order to analyze the outcomes. A post-hoc power calculation (PHP) was performed for each group where no associations were found. A value of 0.8 was considered to be an acceptable value for the power calculation. The significance level was limited to values of P < 0.05.
Results The total number of deliveries during the study period was 1890, out of which 1883 (99.6%) met the study
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criteria (two were multiple gestation and three were not Japanese). The mean (±standard deviation, SD) age of the women was 30.5 (±5.1) years. The mean prepregnancy BMI was 20.7 (±2.9) kg/m2. The parity ranged 0–5, and 925/1883 (49.1%) women were primipara. The mean (±SD) GWG was 10.3 (±3.7) kg. The mean (±SD) length of gestation was 39.4 (±1.2) weeks. In this study, 59 (3.1%) patients were diagnosed with PIH, 22 (1.2%) patients were diagnosed with GDM and seven (0.37%) patients were diagnosed with abnormal placentation.
Pre-pregnancy BMI Table 1 shows the categories of pre-pregnancy BMI and GWG in accordance with the WHO classification and IOM recommendations. Table 2 shows the characteristics of the study population classified by the pre-pregnancy BMI. Table 3 shows the adjusted OR for pregnancy complications according to the prepregnancy BMI. The significant results of prepregnancy BMI were higher rates of PIH, GDM and PPH with vaginal delivery (VD) for the obese group and higher rate of SGA and lower rate of LGA for the underweight group. The pre-pregnancy BMI was classified as underweight in 377 of the 1883 subjects (20%), as normal weight in 1204 (63.9%), as overweight in 152 (8.1%) and as obese in 150 (8.0%). The underweight group was younger and the obese group was older than the normal group. The obese group had a lower rate of primipara (underweight, 49.6%; normal weight, 51.3%; overweight, 55.3%; obese, 34.7%). The rates of deliveries after the 41st week and ECS did not show any significant differences between the groups (PHP, 0.06–0.47). The rates of PIH in the overweight and obese groups were higher than those observed in the normal weight group (adjusted OR, 3.21 and 6.68 [95% CI, 1.29–7.24 and 3.31–13.3]). The rate of PIH was not significantly different between the underweight and normal groups (PHP, 0.12). The regression analysis showed a correlation between the pre-pregnancy BMI and the frequency of PIH (R2 = 0.057, P < 0.001). The rate of GDM in the obese group was higher than that observed in the normal weight group (adjusted OR, 3.12 [95% CI, 1.01– 8.76]). It was especially apparent in obese women with a BMI of greater than 30 kg/m2 (adjusted OR, 8.97; 95% CI, 2.70–29.9). The values observed in the underweight and overweight groups were not significantly different (PHP, 0.01–0.17). The regression analysis revealed a smaller correlation between the pre-pregnancy BMI and the frequency of GDM (R2 = 0.024, P = 0.017). The rate of PPH with VD was higher in the obese group
© 2014 The Authors Journal of Obstetrics and Gynaecology Research © 2014 Japan Society of Obstetrics and Gynecology
Pre-pregnant BMI and GWG
Table 2 Characteristics of the study population BMI (kg/m2)
Underweight,
doi:10.1111/jog.12353
J. Obstet. Gynaecol. Res. Vol. 40, No. 5: 1296–1303, May 2014
Associations between the pre-pregnancy body mass index and gestational weight gain with pregnancy outcomes in Japanese women Tomohito Tanaka1,2, Keisuke Ashihara1, Michihiko Nakamura1, Takayoshi Kanda1, Daisuke Fujita2, Yoshiki Yamashita2, Yoshito Terai2, Hideki Kamegai2 and Masahide Ohmichi2 1
Department of Obstetrics and Gynecology, National Hospital Organization Osaka Minami Medical Center, Kawachinagano, and 2Osaka Medical College, Takatsuki, Japan
Abstract Aim: To examine the associations between the pre-pregnancy body mass index (BMI) and gestational weight gain (GWG) with pregnancy outcomes in Japanese women. Methods: The medical records of 1883 Japanese women who delivered singleton infants from January 2010 to January 2013 at Osaka-Minami Medical Center were retrospectively reviewed. We use the BMI classification which the World Health Organization defined for Asian populations and the GWG classified based on the current 2009 Institute of Medicine (IOM) recommendations. The odds ratio (OR) of each of the groups for the different pregnancy outcomes were compared to the recommended group using a logistic regression analysis adjusted by age, gestational weeks, parity, weight gain, mode of delivery, pregnancy induced hypertension (PIH) and gestational diabetes mellitus. Results: Women who were obese (BMI, ≥25 kg/m2) and overweight (BMI, 23–24.9 kg/m2) had a higher rate of developing PIH (adjusted OR, 6.68 and 3.21 [95% confidence interval [CI], 3.31–13.3 and 1.29–7.24]). In contrast, GWG exhibited a correlation with the weight of the infant. The inadequate GWG group had a higher rate of small-for-gestational age (SGA) infants (adjusted OR, 1.72 [95% CI, 1.22–2.46]). The rate of emergency cesarean section was not significantly different between the groups. Conclusion: A pre-pregnancy BMI less than 23 kg/m2 is desirable to prevent Japanese women from developing PIH. GWG within the IOM recommendations also reduced the risk of PIH and SGA. Key words: body mass index, Institute of Medicine, Japanese, pregnancy outcome, weight gain.
Introduction The recommendations for gestational weight gain (GWG) have been highly controversial in the world. In 1990, a report from the Institution of Medicine (IOM) confirmed a strong association between the GWG and infant size and provided target ranges of recommended weight gains based on the pre-pregnancy
body mass index (BMI).1 In 2009, the IOM reexamined the guidelines for GWG issued in 19902 using the BMI classification developed by the World Health Organization (WHO) and adopted by the National Heart, Lung and Blood Institution.3 In Japan, women have become slimmer year by year. More than 20% of Japanese women in their 20s are underweight, a percentage much higher than that in
Received: September 19 2012. Accepted: October 31 2013. Reprint request to: Dr Tomohito Tanaka, Department of Obstetrics and Gynecology, Osaka Medical College, 2-7 Daigaku-machi, Takatsuki, Osaka 569-8686, Japan. Email: [email protected]
1296
© 2014 The Authors Journal of Obstetrics and Gynaecology Research © 2014 Japan Society of Obstetrics and Gynecology
Pre-pregnant BMI and GWG
most developed countries.4,5 As for obesity, which the WHO has defined as a BMI over 30 kg/m2, the prevalence of obesity in Japan is no more than 2–3%, in contrast to the 10–20% observed in Europe and the USA. Although the prevalence of obesity (BMI, ≥30 kg/ m2) has changed little over the past 40 years in Japan, the incidence of obesity-related chronic diseases, such as diabetes, hypertension and hyperlipidemia, has increased.6 Thus, obesity defined by the WHO may not apply to Asian women. Some authors have suggested the use of a modified BMI classification, and the WHO has defined a BMI classification for Asian populations.6,7 This classification proposes a criteria for obesity of a BMI over 25 kg/m2 and that for an overweight status of a BMI between 23 and 25 kg/m2 for people from the Asia–Oceania region, because data have shown that the incidence of obesity-related diseases significantly increases in subjects with a BMI of 23 kg/m2 or more. However, the appropriate level of GWG in Asian women, including Japanese women, remains controversial. We retrospectively examined the associations between the pre-pregnancy BMI and the GWG with the pregnancy outcomes in Japanese women. This study is based on the IOM recommendations for the Asian population, after changing the thresholds for being overweight and obesity.
Methods After obtaining institutional review board approval, the medical records of Japanese women who delivered at Osaka-Minami Medical Center in Kawachinagano Japan between January 2010 to January 2013 were retrospectively reviewed. The aim of this study was to examine the odds ratio (OR) of each group for pregnancy outcomes compared to the recommended group using the WHO classification7 and IOM guidelines.2 A total of 1883 pregnant women were enrolled in this
study. The hospital is not a tertiary facility. All of the women were delivered between 35 and 42 weeks of gestation, and women with multiple gestation, underlying diseases or complications and those with preterm birth do not deliver at our hospital. Therefore, the women enrolled in this study comprised a low-risk population. The women who were not Japanese were also excluded. Each subject reported her prepregnancy weight at the first medical examination. The height and end of pregnancy weight were measured at admission for delivery. The pre-pregnancy BMI and GWG were calculated by these values. The gestational age was estimated from the last menstrual period, which was confirmed or corrected by ultrasound examinations. All the women were categorized according to the WHO classification7 and IOM guidelines;2 for those with a BMI of less than 18.5 kg/m2 (underweight), the total recommended weight gain was between 12.5 and 18 kg; for those with a BMI between 18.5 and 22.9 kg/m2 (normal weight), the total recommended weight gain was between 11.5 and 16 kg; for those with a BMI of between 23 and 24.9 kg/m2 (overweight), the total recommended weight gain was between 7 and 11.5 kg; and for those who had a BMI of 25 kg/m2 or more (obese), the total recommended weight gain was between 5 and 9.1 kg. The women with a GWG within the IOM recommendation were categorized as having an adequate GWG. The women with a GWG less than the IOM recommendation were categorized as having an inadequate GWG. The women with a GWG greater than the IOM recommendation were categorized to have an excessive GWG (Table 1). The incidence rates of pregnancy-related complications, including pregnancy-induced hypertension (PIH), gestational diabetes mellitus (GDM), small-forgestational age (SGA) and large-for-gestational age (LGA) infants were examined in each group. The duration of labor and the rate of post-partum hemorrhage (PPH), emergency cesarean section (ECS), delivery
Table 1 Pre-pregnancy BMI and GWG categories GWG category
Pre-pregnancy BMI category BMI 1000 mL) after delivery. The duration of labor was defined as the length of time from the onset of labor, which was defined as regular and painful uterine contractions, to the delivery of the placenta. The neonatal outcome was evaluated by the rates of a low Apgar score and intrauterine fetal death (IUFD). All of the statistical analysis was performed using the JMP software package (version 9.0.2). The continuous variables were expressed as the means ± standard deviations as determined by an anova. The clinical characteristics and obstetric outcomes of the categorical data or the frequency of an event were analyzed using Fisher’s exact test and the χ2-test with Yates’ correction, respectively. Simple regression analysis was used to examine the associations between pre-pregnancy BMI or GWG and pregnancy events. A multiple logistic regression analysis model was also used to calculate adjusted OR and 95% confidence intervals (CI). Maternal age, parity, length of gestation, mode of delivery, PIH, GDM and GWG were considered to be confounding factors. The models were adjusted for these factors in order to analyze the outcomes. A post-hoc power calculation (PHP) was performed for each group where no associations were found. A value of 0.8 was considered to be an acceptable value for the power calculation. The significance level was limited to values of P < 0.05.
Results The total number of deliveries during the study period was 1890, out of which 1883 (99.6%) met the study
1298
criteria (two were multiple gestation and three were not Japanese). The mean (±standard deviation, SD) age of the women was 30.5 (±5.1) years. The mean prepregnancy BMI was 20.7 (±2.9) kg/m2. The parity ranged 0–5, and 925/1883 (49.1%) women were primipara. The mean (±SD) GWG was 10.3 (±3.7) kg. The mean (±SD) length of gestation was 39.4 (±1.2) weeks. In this study, 59 (3.1%) patients were diagnosed with PIH, 22 (1.2%) patients were diagnosed with GDM and seven (0.37%) patients were diagnosed with abnormal placentation.
Pre-pregnancy BMI Table 1 shows the categories of pre-pregnancy BMI and GWG in accordance with the WHO classification and IOM recommendations. Table 2 shows the characteristics of the study population classified by the pre-pregnancy BMI. Table 3 shows the adjusted OR for pregnancy complications according to the prepregnancy BMI. The significant results of prepregnancy BMI were higher rates of PIH, GDM and PPH with vaginal delivery (VD) for the obese group and higher rate of SGA and lower rate of LGA for the underweight group. The pre-pregnancy BMI was classified as underweight in 377 of the 1883 subjects (20%), as normal weight in 1204 (63.9%), as overweight in 152 (8.1%) and as obese in 150 (8.0%). The underweight group was younger and the obese group was older than the normal group. The obese group had a lower rate of primipara (underweight, 49.6%; normal weight, 51.3%; overweight, 55.3%; obese, 34.7%). The rates of deliveries after the 41st week and ECS did not show any significant differences between the groups (PHP, 0.06–0.47). The rates of PIH in the overweight and obese groups were higher than those observed in the normal weight group (adjusted OR, 3.21 and 6.68 [95% CI, 1.29–7.24 and 3.31–13.3]). The rate of PIH was not significantly different between the underweight and normal groups (PHP, 0.12). The regression analysis showed a correlation between the pre-pregnancy BMI and the frequency of PIH (R2 = 0.057, P < 0.001). The rate of GDM in the obese group was higher than that observed in the normal weight group (adjusted OR, 3.12 [95% CI, 1.01– 8.76]). It was especially apparent in obese women with a BMI of greater than 30 kg/m2 (adjusted OR, 8.97; 95% CI, 2.70–29.9). The values observed in the underweight and overweight groups were not significantly different (PHP, 0.01–0.17). The regression analysis revealed a smaller correlation between the pre-pregnancy BMI and the frequency of GDM (R2 = 0.024, P = 0.017). The rate of PPH with VD was higher in the obese group
© 2014 The Authors Journal of Obstetrics and Gynaecology Research © 2014 Japan Society of Obstetrics and Gynecology
Pre-pregnant BMI and GWG
Table 2 Characteristics of the study population BMI (kg/m2)
Underweight,
