**2. Optimal birth weight for low neonatal mortality rate**

Birth weight is the single strongest predictor of infant survival. One determinant of birth weight is gestational age: as the fetus matures, it grows. The other determinant is gestational age, because birth weight is a summary of fetal growth. Susser et al. (1972) reported that when gestational age and weight are analyzed simultaneously, birth weight accounts for 90% of the variance of perinatal mortality, whereas gestational age accounts for barely 5%. On the other hand, Wilcox & Skjaerven (1992) stated that an infant benefits as much from an increase in gestational age as from an increase in its weight, relative to the weights of others at the same gestational age.

Birth weight between the 10th and 90th percentile has been generally accepted as appropriate fetal growth and classified as an appropriate gestational age (AGA) infant. However, what birth weight range in single term infants is optimal to reduce the neonatal mortality rate? National weight-for-gestational-age charts are created from the weight distributions of livebirths at each age using population-based data from each country. According to Japanese Vital Statistics, the lowest early neonatal mortality rate per 1000 live births in 2005 was 0.3 for infants weighing 3,000–3,999 g. The rate increased with decreasing birth weight: 0.4 for 2,500–2,999 g, 1.7 for 2,000–2,499 g and 10.9 for 1,500–1,999 g (Ministry of Health, Labour and Welfare, Japan, 2006).

The National Center for Health Statistics in the United States reported similar findings for the year 1995–2002, using singletons data (Joseph et al., 2009). For centuries, gestational maturity has been understood as important to infant survival. Research establishing an association between birth weight and neonatal morbidity/ mortality rates in term livebirth infants is limited. Joseph et al. (2009) show the birth weight-specific rates of serious neonatal morbidity and neonatal mortality in 17,554,934 livebirths from perinatal mortality data files of the National Center for Health Statistics for the years 1995-2002. All were singleton livebirths with a clinical estimate of gestation between 36 and 42 weeks born to white or black mothers in the United States (Figure 1). Based on empirical observation, birth weightspecific patterns of serious neonatal morbidity or neonatal death follow a specific pattern, that is, that neonatal morbidity/mortality rates decrease exponentially with increasing birth weight in the LBW range. This declining pattern changes to a flat, stable rate at "optimal" birth weight before serious neonatal morbidity/neonatal mortality rates increase with increasing birth weight. In the regression model, the low optimal birth weight at 40 weeks' gestation was 2,982 g (95% confidence interval (CI): 2,965-2,999 g) for females and 3,012 g (95% CI: 3,008-3,018 g) for males. Similarly, the high end of optimal birth weight range was 3,813 g (95% CI: 3,774-3,852 g) for females and 3,978 g (95% CI: 3,976-3,980 g) for males.

Source; Reference [Joseph KS., et al.,2009]

28 From Preconception to Postpartum

Numerous factors are associated with birth weight, such as parity and the sex of the child (Bonellie et al., 2008), maternal and gestational diabetes (Langer et al., 2005), maternal smoking during pregnancy (Ward et al., 2007), maternal overweight status (Larsen et al., 1990), and gestational weight gain (GWG) (Kiel et al., 2007). Of these factors, previous studies have suggested particularly that both prepregnancy body mass index (BMI; weight (kg)/ height (m) 2) and GWG are positively associated with birth weight in the offspring and are related to risks of both low and high offspring birth weight (Brown et al., 2002; Rode et al., 2007). Women with a normal prepregnancy BMI and those who meet the recommended weight gains are healthiest and have healthier children. Adequate GWG contributes to better pregnancy outcomes in both mothers and infants, for short- and long-term health. Prepregnancy BMI and GWG management may be a key factor influencing the health of women during pregnancy and the development of the fetus. This review focuses on the

Birth weight is the single strongest predictor of infant survival. One determinant of birth weight is gestational age: as the fetus matures, it grows. The other determinant is gestational age, because birth weight is a summary of fetal growth. Susser et al. (1972) reported that when gestational age and weight are analyzed simultaneously, birth weight accounts for 90% of the variance of perinatal mortality, whereas gestational age accounts for barely 5%. On the other hand, Wilcox & Skjaerven (1992) stated that an infant benefits as much from an increase in gestational age as from an increase in its weight, relative to the weights of others

Birth weight between the 10th and 90th percentile has been generally accepted as appropriate fetal growth and classified as an appropriate gestational age (AGA) infant. However, what birth weight range in single term infants is optimal to reduce the neonatal mortality rate? National weight-for-gestational-age charts are created from the weight distributions of livebirths at each age using population-based data from each country. According to Japanese Vital Statistics, the lowest early neonatal mortality rate per 1000 live births in 2005 was 0.3 for infants weighing 3,000–3,999 g. The rate increased with decreasing birth weight: 0.4 for 2,500–2,999 g, 1.7 for 2,000–2,499 g and 10.9 for 1,500–1,999 g (Ministry

The National Center for Health Statistics in the United States reported similar findings for the year 1995–2002, using singletons data (Joseph et al., 2009). For centuries, gestational maturity has been understood as important to infant survival. Research establishing an association between birth weight and neonatal morbidity/ mortality rates in term livebirth infants is limited. Joseph et al. (2009) show the birth weight-specific rates of serious neonatal morbidity and neonatal mortality in 17,554,934 livebirths from perinatal mortality data files of the National Center for Health Statistics for the years 1995-2002. All were singleton livebirths with a clinical estimate of gestation between 36 and 42 weeks born to white or black mothers in the United States (Figure 1). Based on empirical observation, birth weightspecific patterns of serious neonatal morbidity or neonatal death follow a specific pattern, that is, that neonatal morbidity/mortality rates decrease exponentially with increasing birth weight in the LBW range. This declining pattern changes to a flat, stable rate at "optimal" birth weight before serious neonatal morbidity/neonatal mortality rates increase with

effect of prepregnancy BMI and adequate GWG on birth weight.

**2. Optimal birth weight for low neonatal mortality rate** 

at the same gestational age.

of Health, Labour and Welfare, Japan, 2006).

Fig. 1. Birth weight specific rates of serious neonatal morbidity and neonatal mortality at 37 weeks' gestational age among singletons

The optimal birth weight range may vary according to the age, race, ethnicity, and size of the mother, as maternal growth constraint may protect the health of the mother and baby. A study of 16.4 million women using the National Center for Health Statistics' 1983-1987 national lived birth/infant death data sets, examined the association between birth weight and neonatal mortality rate in adolescent (aged 15-18 years) and adult mothers (aged 19-34 years) of black and white race. Minimum neonatal mortality rates occurred at the same birth weight (3,500 to 4,499 g white and 3,000 to 3,999 g black) whether mothers of the infants were adolescents or adults. The most favorable range of birth weight, in which survival was greatest, commenced at 3,000 g for all mothers and terminated at 3,999 g for most black adolescents and black adults, at 4,499 g for most white adolescents, and at 4,999 g for white adults. Of infants born to mothers < or = 16 years old, 33% were lighter and 1.5% were heavier than the favorable birth weight range (Rees et al., 1996). Assisting mothers to bear infants with birth weight in the optimal weight range corresponding with low neonatal mortality in each country is an appropriate goal of clinical management. 1983-1987

#### **3. Optimal weight gain recommendation**

Adequate weight gain by prepregnancy BMI is important for optimal pregnancy outcomes. The Institute of Medicine (IOM) released new gestational weight guidelines (IOM, 2009) to reinforce those released in 1990 (IOM, 1990), because many key aspects of the health of women of childbearing age have changed, such as the increasingly high rates of overweight and obese women, increasing GWG, and the increasing age of women becoming pregnant. There are several salient differences. First, the new guidelines change the BMI categories to those commonly used for other adult health outcomes. Second, they provide a closed gestational weight gain range for obese women, based on data from women with BMI values of 30-34.9 kg/m2.

The Effect of Prepregnancy Body Mass Index and Gestational Weight Gain on Birth Weight 31

nourished (Saldana et al., 2004). Overweight status and obesity have become serious global public health issues. Nearly two thirds of reproductive-aged women in the United States are currently overweight or obese (≥25 kg/m2). In the National Health and Nutrition Examination Survey (NHANES), the prevalence of obesity (BMI ≥30 kg/m2) in women aged

20-49 years continues to be high, exceeding 30% after 1999 (Flegal et al., 2010)(Fig. 2).

BMI categories (kg/m2); Underweight, <18.5; Normal, 18.5-24.9; Overweight, 25.0-29.9; Obese, ≥30.0. Fig. 2. Trends of underweight, normal, overweight, and obese among U.S. women aged 20-40 y

In the latest NHANES data from 2007-2008 of 877 women aged 20-39 years, the prevalence of overweight status (BMI ≥25 kg/m2) and obesity were 59.5% and 34.0%, respectively. Trends are similar by age. The prevalence in all classes of obesity [(class I (30–34.9 kg/m2), class II (35–39.9 kg/m2), and class III (≥40 kg/m2) )] is lowest in white, non-Hispanic women, and highest in non-Hispanic black women in the United States (Flegal et al., 2010). Other developed countries have observed similar trends. In Australia in 2007-2008, 44.5% women aged 25-34 years and 55.3% women aged 35-44 years were overweight or obese, which constituted a marked increase over the previous 20 years (Australian Institute of Health and Welfare, 2010). In the UK, more than 50% of women in the reproductive age category of 25-44 years are overweight or obese. There has been a 69% increase in maternal obesity from 1990 to 2004, a period of only 15 years (Heslehurst et al., 2007). Thus, the increased number of overweight and obese reproductive-aged women is a worldwide

The prevalence of underweight status (BMI<18.5 kg/m2) was only 3.1 % of reproductiveaged women in 2005-2006 (Flegal et al., 2010). Underdeveloped regions, such as South Asia or Africa, where undernutrition is generally highest, or there are socio-economic characteristics or food poverty, report the highest prevalence of underweight women (Macro International Inc, 2007). However, even some developed countries such as Japan show high prevalence rates. Over the last two decades in Japan, the prevalence of underweight women has increased from 19.6% to 21.2% in those aged 20-29 years, and from 8.6% to 13.3% in those aged 30-39 (Hayashi et al., 2006). A low body mass index in highly

phenomenon.

%

**4.2 The prevalence of underweight women** 

According to the new guideline, underweight women (BMI<18.5 kg/m2) should gain 12.5- 18.0 kg during pregnancy, normal weight women (BMI 18.5-24.9 kg/m2) should gain 11.5- 16.0 kg, and overweight women (BMI 25.0-29.9 kg/m2) should gain 7.0-11.5 kg. This is the standard for weight gain worldwide (IOM, 2009) (Table 1). This guideline will be used in clinical practice as an effective weight management tool, and it will help to evaluate the association between these gestational weight ranges and pregnancy outcomes worldwide. Weight gain within the guidelines has been associated with healthy fetal and maternal outcomes.


\* Calculations assume a 0.5-2 kg (1.1-4.4 lbs) weight gain in the first trimester

Source; Reference [Institute of Medicine, 2009]

Table 1. 2009 IOM recommendations for total and rate of weight gain during pregnancy by prepregnancy BMI

In the 1990 IOM guideline, two thirds of women exceeded the recommended weight gain (Schieve et al., 1998). In a study of over 4,000 women from the University of California's San Francisco Perinatal Database, 23% of underweight women, 49% of normal-weight women, and 70% of overweight women exceeded the 1990 IOM recommendations (Carmichael et al., 1997). On the other hand, newly released, 2009 IOM recommendations were assessed by Park et al. (2011) in a population-based, retrospective cohort study of 570,672 women with singleton, full-term livebirths in Florida from 2004 to 2007. They found that 31.6% of underweight women, 42.8% of normal-weight women, and 65.0% of overweight women exceeded the 2009 IOM recommendations. These results suggest that interventions including nutritional education and behavioral strategies to promote healthy and appropriate weight gain during pregnancy should approach obese women in particular.
