Percent of non-pregnant women of reproductive age who have a low body mass index (BMI <18.5)
The percent of non-pregnant women ages 15 to 49 who have a body mass index (BMI) that is less than 18.5 kg/m2. BMI is the ratio of weight to height squared (kg/m2) and a low BMI measures thinness and possible chronic energy deficiency in non-pregnant women.
This indicator is calculated as:
(Number of non-pregnant women ages 15 to 49 with a BMI <18.5 / Total number of non-pregnant women between the ages of 15-49) x 100
BMI is calculated as: Weight in kilograms / (Height in meters)2
There are numerous tools (charts, websites, and computer applications) available to calculate BMI.
The standard cut-off for underweight in non-pregnant, non-lactating women aged 15-49, determined by WHO (2004) and used by the Institute of Medicine (IOM, 2009) is a BMI of <18.5. Further cutoffs for categories of underweight are listed below:
- Severe thinness <16.00
- Moderate thinness 16.00 – 16.99
- Mild thinness 17.00 – 18.49
For the full BMI reference table, see WHO Global Database for BMI (2010).
Measurement of weights and heights of non-pregnant women of reproductive age. Data may be disaggregated by age grouping, levels of underweight based on WHO cutoffs, by lactation status for postpartum women, and, where data are available, by relevant socioeconomic and demographic factors such as education, income, and urban/rural residence.
Population-based surveys; surveillance systems; health facility records
A well-accepted measure of weight status, BMI is a self-contained ratio highly correlated with weight-for-height that does not require reference tables for interpretation. Although this indicator specifies non-pregnant women, BMI during early pregnancy is commonly used to identify women who need to gain more weight in order to improve infant outcomes of pregnancy including, intrauterine growth retardation (IUGR), low birth weight (LBW), and perinatal mortality. This indicator relates to three of the Millennium Development Goals: #1. Reduce poverty and hunger; #4. Reduce child mortality; and #5. Improve maternal health.
The consequences of undernutrition for women and for their offspring are serious and often long-term. Women experiencing moderate to severe thinness also are more likely to have vitamin and mineral deficiencies with accompanying anemia, goiter, possible immune suppression, and reduced well-being and productivity. In a series of studies and meta-analyses, the Maternal and Child Undernutrition Study Group has estimated that 22 percent of childhood deaths can be attributed to childhood underweight and maternal low BMI functioning through IUGR to affect LBW (Black et al., 2008). Based on data from prospective studies in five countries, Victoria, et al. (2008) found that the effects of undernutrition can span at least three generations. There were small but significant associations between grandmother’s heights and their grand children’s birth weight from the five cohorts.
Stunting of height in adolescent to adult women is associated with undernutrition during their early childhood and has effects on pregnancy outcome independent of BMI. Severe stunting (height <145 cm) and short stature (146 to 157 cm) increase risk of caesarean delivery largely linked to cephalopelvic disproportion (WHO, 1995). Low BMI does not appear to increase the risk of pregnancy complications, whereas, short stature and higher BMI together can increase these complications and need for assisted delivery (Cnattingius et al., 1998).
An alternative indicator to BMI in situations where it is impractical to get weight and height data is the mid-upper arm circumference, which is based on a single anthropometric measure (See Women’s Nutrition indicator ‘Percent of women with low mid-upper arm circumference’).
A related (additional) indicator to BMI is the woman’s weight, which reflects both acute and chronic nutritional stresses. The cut point for identifying women who are undernourished is 45 kg (ACC/SCN, 1992).
BMI may present difficulties to some field workers in service delivery programs because of the mathematical calculations required. Tools (e.g., tables, wheels) have been developed to assist with these calculations and, more recently, website, computer, and phone applications are available to calculate BMI. Rapid changes in anthropometric measures as a result of the adolescent growth spurt complicate assessing the nutritional status of those below 18 years of age (i.e., it increases the variance in BMI). Despite this caveat, BMI is recommended for use with adolescents.
Because BMI varies with body proportions or the Cormic index (sitting height divided by standing height), some have argued that data on sitting height should be collected where possible and that the BMI should be adjusted for the Cormic index. However, others consider this adjustment to be impractical, given that the calculation of BMI itself is methodologically challenging to some field workers.
nutrition, safe motherhood (SM)
In cultural settings such as South Asia where women often eat ‘last and least,’ even in households with adequate food available, adolescent and young women may be chronically undernourished. Thus, women frequently enter pregnancy undernourished and become more so throughout pregnancy. Undernourished pregnant women are at much greater risk of poor birth outcomes than are nourished women. They are more likely to be vitamin A-deficient and to be anemic, both of which also increase the risk of maternal and fetal morbidity and mortality. Education and communication efforts directed toward parents, husbands, mothers-in-law, and communities can address the need to provide more nutritious foods for undernourished girls and women, thereby benefitting their health in the short term and promoting better pregnancy and birth outcomes in the future.
ACC/SCN, 1992, Second Report on the World Nutrition Situation, Geneva: ACC/SCN.
Black, RE, Allen, LH, Bhutta, ZA, Caufield LE, de Onis, M, Ezzati, M, Mathers, C, Rivera, J,, “Maternal and child undernutrition: global and regional exposures and health consequences,” Lancet 2008; 371: 243-260.
Cnattingius R, Cnattingius S, Notzon FC, Obstacles to reducing cesarean rates in a low-cesarean setting: the effect of maternal age, height, and weight. Obstet Gynecol. 1998 Oct;92(4 Pt 1):501-6.
Institute of Medicine (IOM) and National Research Council, 2008, Weight Gain during Pregnancy: Reexamining the Guidelines, Eds: Kathleen Rasmussen and Ann Yaktine, Washington, D.C.: The National Academy Press. http://www.ncbi.nlm.nih.gov/pubmed/20669500
Victora, CG, Adair, L, Fall, C, Hallal, PC, Martorell, R, Richter, L, Sachdev, HS, , “Maternal and child undernutrition: consequences for adult health and human capital,” Lancet 2008; 371: 340–57.
WHO, Maternal anthropometry and pregnancy outcomes: A WHO Collaborative Study, World Health Organization Supplement 1995: 73:32-37.
WHO, 2010, A Review of Nutrition Policies: Draft Report, Geneva: WHO.
WHO Global Database for Body Mass Index. http://apps.who.int/bmi/index.jsp?introPage=intro_3.html