Adaptation of a woman’s body to pregnancy and postpartum: requirement for energy and elements

VIDEO 4

Energy intake requirements in pregnancy match the demands of resting metabolism, physical activity and tissue growth. Energy balance in pregnancy is, therefore, defined as energy intake equal to energy expenditure plus energy storage. A detailed understanding of these components and their changes throughout gestation can inform energy intake recommendations for minimizing the risk of poor pregnancy outcomes.

In pregnancy, the mother's body has to adapt to support not only her own metabolic needs but also the development of the placenta and growing fetus. Each of these three compartments, mother, placenta and fetus, has its own metabolism, the collective aim of which is to provide nutrients and oxygen to the developing fetus.

Moreover, pregnancy is a dynamic state, which can be divided in two periods, with the first part defined as anabolic, mainly due to fat storage, and the second part as catabolic, when nutrients are made available to be transferred to the fetus for its phase of exponential growth. These changes are related to increased insulin sensitivity in the first months, while in the second half of pregnancy there is increased insulin resistance, leading to higher levels of fats in the maternal blood. By contrast, the placenta grows proportionally more in mass in the first part of pregnancy while, in the second part, there is a continuous maturation of transport systems and a reduced distance between maternal and fetal blood. Fetal body composition changes as well, with a significant increase in fetal fat mass in the final months of pregnancy.

All these adaptations affect energy intake requirements that need to increase to match the demands of resting metabolism, physical activity and tissue growth. Energy balance in pregnancy is, therefore, calculated by accounting for the increased needs, their changes throughout gestation and how they relate to potential risk of poor pregnancy outcome.

Maternal prepregnancy body mass index (BMI) and maternal diet and nutritional status are major predictors of pregnancy outcome. Maternal BMI is primarily influenced by energy intake, which reflects macronutrient consumption, while the significance of maternal diet and nutritional status lies in diet quality, which is largely determined by micronutrient content.

Energy intake in pregnancy refers to the dietary intake that is required to achieve optimal health outcomes. A key factor for achieving optimal pregnancy outcomes is energy balance or the relationship between energy intake, expenditure and storage in maternal and fetal tissues. Increased energy intake is needed in pregnancy for: deposition of new maternal, placental and fetal tissues, triglycerides deposition in maternal fat tissue and increased maternal and fetal metabolic needs.

A detailed understanding of the components of energy requirements and their changes throughout gestation can inform energy intake recommendations for minimizing the risk of poor pregnancy outcomes. For achieving optimal pregnancy outcomes, women with low body weight require more fat mass accumulation than women with obesity, who do not require fat-mass accumulation at all. Given the high energy density of fat mass, these differences greatly affect energy intake requirements for a healthy pregnancy. In contrast, the energy stored in fetal and placental tissues is comparable between all women and has minimal impact on energy requirements.

There are different national recommendations for increased calorie intake during pregnancy, and in relation to the different needs of increased energy intake. Gestational weight gain recommendations also vary according to prepregnancy BMI. With progressive increase in BMI, recommended gestational weight gain becomes lower, the recommendation in severely obese women being below 5 kg of total weight gain during pregnancy.

Neonatal adiposity is strongly and positively associated with maternal prepregnancy BMI and may have long-term consequences, including an increased risk of developing metabolic syndrome later in life. Gestational weight gain outside the recommended range may also have an impact on pregnancy complications: 1) higher maternal prepregnancy BMI and gestational weight gain are associated with higher risks of gestational hypertensive disorders, gestational diabetes and being large-for-gestational age at birth; 2) preterm birth risk is increased at lower and higher BMI and weight gain and 3) in general, obese mothers with high gestational weight gain have the highest risk of any pregnancy complication. 

 In addition to quantity, the quality of nutrition is important in pregnancy. Overall, the distribution requirement of macronutrients is not different from that of the diet of a healthy, normal-weight woman, but 1) for carbohydrates, it is recommended to opt for those with a low glycemic index and, in general, to reduce sugars (simple sugars < 15% of energy intake); 2) proteins should be of high quality and 3) for fats, attention should be paid to achieving a correct balance between saturated and unsaturated foods, and, in particular, intake of docosahexaenoic acid (DHA), which is a critical omega-3 fatty acid, should be optimized.

Many studies over the last decade have highlighted the relevance of dietary pattern during pregnancy. It has been shown that certain foods, such as organic vegetables and probiotic milk products, and dietary patterns rich in vegetables, fruits, healthy oils, whole grains and water, are associated with a reduced risk of pre-eclampsia, small-for-gestational-age infants, preterm delivery and congenital anomalies. Conversely, the Western diet, which is high in processed meat and fats and refined bread, and low in fruit and vegetables, as well as the consumption of sugar-sweetened beverages, salty and sweet snacks and fish rich in mercury, increase the risk of pre-eclampsia, small-for-gestational age and preterm delivery.

These differences are due to the proportion of micronutrients in these diets. During pregnancy, the recommended intake of some micronutrients increases more than does energy intake, particularly for the Group-B vitamins (like folate), iron and iodine. As the increased needs of micronutrients in pregnancy may not be achieved by diet alone, supplementation with iron and folate is recommended by all international bodies. Evidence regarding other micronutrients also highlights the need for supplementation with vitamin D and iodine from preconception to throughout pregnancy, along with additional calcium during lactation.

Lactation is often a neglected period, during which mothers may experience depression. However, it is also the time when breastfeeding begins, which is positively associated with both successful lactation and postpartum weight loss. The increased energy requirement for lactation is approximately 500 kcal/day, more than during pregnancy, for the growing neonate and also for the endocrine changes that lead to mobilization of fat from the maternal tissues, allowing the mother to return progressively to her prepregnancy metabolic state.

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