The subcommittee included several kinds of data in its review. Studies that have focused on women's employment rather than physical activity per se were reviewed, and their relevance to the subcommittee's task was assessed. then, to have a broad perspective, reports of energy expenditure research were examined for pregnant and nonpregnant women in developing countries, and to the extent that data were available, consideration was given to the type and duration of physical activity performed. Information on the dietary, metabolic, physiological, and endocrine adaptations to pregnancy in well-nourished women was also reviewed as they pertain to energy expenditure and physical activity.

Most of the data on maternal work and employment were from developed countries. there are some problems in extrapolating these data to developing countries as the kinds of work that are most taxing would be most relevant and would differ from that in developed countries. Data on the impact of physical activity on cardiovascular and placental function were examined to determine their significance for the mother, the fetus, and the newborn infant. Animal studies and epidemiological research pertaining to gestational duration, fetal growth, fetal loss, and congenital malformations were also included. The subcommittee also reviewed the available data on the impact of physical activity on lactation as an outcome of pregnancy and on maternal postpregnancy nutritional status.

In general, the subcommittee concluded that field-based studies are needed to quantify the intensity, frequency, and effort of physical activity under natural conditions during pregnancy. These studies should include changes that occur during the course of pregnancy, including their effect on different outcome measures such as maternal and infant morbidity and mortality. Presently, very few studies on humans or even animals shed any light on this topic.

Many women in developing countries are chronically malnourished, as demonstrated by stunting, low weight-for-height, and low fat stores. They are also more likely to have iron deficiency anemia. In part because of increases in maternal weight during pregnancy, the energy cost of weight-bearing tasks also increases. These findings are highlighted throughout the report. It is intriguing to find that pregnant women in developing countries seem to achieve energy balance despite limited diets and high levels of physical exertion. It is not known if this is due to some adaptive mechanism or to measurement error.

Socioeconomic status, women's employment in rural and urban environments, consequent physical activity, and its effect on the outcome of pregnancy are reviewed in Chapter 2. It is pointed out that both pregnant and nonpregnant women in developing countries perform physical work for prolonged periods of time under unfavorable environmental conditions.

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