Nutrition, weight gain and exercise during pregnancy

During pregnancy, energy, nutrition and liquid requirements increase for an appropriate fetal, placental and maternal tissue growth. A healthy nutrition during pregnancy increases the possibility of an on-term fetal development, an uncomplicated gestational period and labor, and a succesful lactation period while it has a long-term benefit on the maternal health, reducing the risk for postpartum obesity.
Nutrition during pregnancy is influenced by a variety of genetic, social, cultural, economic and personal factors. Therefore, it is very difficult to determine the direct impact of nutrition on the health during pregnancy. Furthermore, it has been seldomly possible to identify the effect of malnutrition directly on the gestational outcomes. Consequently, evidence for the effect of nutrition on the gestational outcomes is obtained by gathering the results from observational studies, laboratory studies, and experimental studies on food. The impact of inadequate or excess intake of a food on the pregnancy may vary depending on the exposure time or the volume. Furthermore, although metabolic changes during the pregnancy ensure maintanence of the nutrients required for fetal requirements, some pregnancies fail to achieve such adaptive changes. The underlying mechanism for these adaptive changes has not been clearly defined yet.(1)
According to the “fetal origins hypothesis” proposed by Barker in 1998, fetal nutrition has a lifelong impact on the metabolism, and it forms an underlying basis for various adult chronic diseases.2 During the last decade, several epidemiological data was obtained demonstrating that birthweight is related with hypertension, glucose intolerance, type II diabetes, coronary heart disease and mortality.3-6 We end up with the restricted fetal growth followed by postnatal catchup growth, resulting in obesity as the most risky pattern for adult chronic disease. However, further studies are needed in order to identify the influence of nutrition during pregnancy, gestational physiology, placental factors and fetal metabolism on the birth weight as well as roles of genetic and enviromental factors.
 

Keywords

Energy Balance and Weight Gain    
During Pregnancy
Significance of a healthy nutrition during pregnancy accounts for the positive linear relationship demonstrated between the maternal weight gain and the neonatal birth weight, and also with the impact of prepregnancy body mass index (BMI) on the neonatal birthweight, independent of the gestational weight gained. The potential to deliver a low birth weight infant (<2500 g) is higher for mothers with a low prepregnancy weight and low weight gain during pregnancy as well as the higher potential to deliver a macrosomic infant for mothers with high prepregnancy weight. In other words, the total calorie intake during pregnancy is the most important nutritional factor known to have influence on the birth weight. During pregnancy, extra energy required in addition to the prepregnancy needs is 330 kkal/day (a total of 80,000 kkal), which corresponds to a maternal weight gain of 10-12 kg in the average term.7 However, in a study by King et al., it has been demonstrated that energy needs can show variations ranging from 0 to 120,000 kkal.8 Although weak or undernourished pregnant women usually need more energy intake, determination of actual energy requirements is not so easy.
Therefore, the most practical way is to use the gestational weight gain as a barometer of the energy intake. Appropriate weight gain is an indication of good energy intake while inadequate or excessive weight gain implies necessity for evaluating the nutritional status along with the introduction of proper improvements.
Appropriate weight gains and speed of weight gain proposed by the Institute of Medicine (IOM) are shown at Table 1.9 In a review by Abrams et al. in 2002, it was observed that the women who gained weight within the limits proposed by IOM had the optimum gestational outcomes in terms of maternal and fetal aspects (low birth weight, macrosomy, rates of spontaneous preterm deliveries, cesarian delivery, maternal postpartum obesity).10 However, only 30-40% of the pregnant women gained weight within the proposed range.
In the same study by Abrams, it has been indicated that the weight gain in the second trimester is more closely associated with the fetal growth compared to the gains in the first and third trimesters, and that low weight gain in the third trimester may be associated with spontaneous preterm delivery. Although the peak energy need is at between weeks 10 and 30, the maternal fat deposited during that period is used for the fetal growth and lactation in the third trimester.(11)
Low weight gain during pregnancy is considered any value less than 0.5 kg/month for obese women, and less than 1 kg/month for non-obese women. Any gain exceeding 3 kg/month is considered excessive.(9)
In spite of all this information, it is very difficult to interpret the gestational weight gain as most of the weight gains of the pregnant women with optimum gestational outcomes are out of the range proposed by IOM.12 Maternal weight gain alone should not be considered as a specific tool to diagnose the negative gestational outcomes. IOM proposes that a target for appropriate weight gain should be defined in the first prenatal visit for each future mother, and all future mothers should be furnished with detailed information on nutrition and physical activity. Pregnant women with a weight gain out of the planned target should be evaluated on their diet and physical activities, and if possible, this evaluation should be carried out by a dietician, consequently taking action to provide necessary improvements. Such improvement will both contribute to the healthy course of the pregnancy and enable prevention of the postpartum obesity.
 
Balanced Diet During Pregnancy
Although energy intake and maternal weight gain during pregnancy are important parameters of the nutritional status, a balanced diet is much more important than the calorie intake. Food density gives the amount of protein, vitamin and minerals included by each 100 kkal food. Even tough processed ready-made food with low food density provides sufficient energy intake, they lack in the required protein, vitamin and mineral intakes. Daily energy increase recommended as 300 kg calorie corresponds to 17% of the prenatal needs; however, need for vitamin and minerals raises up to 20-100%. Therefore, the selection of food should aim not only the lacked energy, but also intake of high density food which can provide increased mineral and vitamin support (e.g. a high density food like milk should be preferred to a low density food like french fries). However, this is not to say that intake of minerals and vitamin is necessary during pregnancy.
It has been shown that high rate of sugar intake is associated with low birth weight infant deliveries and increased preterm delivery rates in low-income adolescents.(13)
Daily protein need is 60 grams during pregnancy with an increase of 15 grams compared to the prepregnancy period.7 Food including protein are also excellent sources of iron, vitamin B6 and zinc. However, animal proteins (red meat, fatty dairy products) lead to fat deposition when they are excessively consumed. Instead of them, food like chicken and fish and light/skim dairy products should be preferred.
Also, although some suggested that high protein intake prevents preecclampsia, no evidence has been shown for the benefits of high protein intake during pregnancy; on the contrary, it has been indicated that excessive intake may be harmful.(14) It has been demonstrated that high amount of protein consumption is associated with preterm delivery and low birth weight infants.
Use of linoleic and a -linoleic acids (omega-3 fatty acids), essential fatty acids, during pregnancy has become the subject of great interest in recent years. Omega-3 fatty acids contribute to the neural and visual development of the fetus. The best sources of omega-3 fatty acids are soy bean and fatty fishes.15-16 However, high consumption of sea products may lead to excessive intake of toxic substances, which are likely to result in neurological anomalies such as methylmercury and polychlorinated biphenyl, and neurodevelopmental delay.(17)
It has been claimed that trans-fatty acids in margarines and ready foods like cakes and biscuits may damage normal metabolism of the fatty acids; they may increase the risk of heart disease in adults; and they may reduce the fetal birth weight and the head circumference.(18j) Consequently, further studies should be conducted to identify the required amount and type of fatty acids to be used during pregnancy. Furthermore, it is not known whether support of fish oil is safe or not, and effects of consuming trans-fatty acids are still obscure. In the meantime, pregnant women should be advised that they should meet their fat requirements from unhydrogenated vegetable oils, and consume fish products in moderate amounts, and prefer unprocessed natural food.
 
Increased Vitamin-Mineral
Needs During Pregnancy
Nutrition during pregnancy is a whole ranging from preconception to postconception period; it influences the health of the infant to be born. Nutritional requirements for protein, calcium, iron, zinc, folate, vitamin D and E, ascorbic acide and vitamin B increase 10-100% during pregnancy. A normal nourished person, who has no malnutrition problem, already meets these requirements in his/her daily diet, but a particular attention should be given. Nutrients that are most questioned during pregnancy are as follows:
 
Sodium
Salt intake during pregnancy should not be restricted; nor an excess consumption should be allowed. In a study where pregnants were given a sodium-poor diet, it was observed that sodium restricton significantly reduced the quality of entire nutrition. It had no negative effect on birth or placental weight while no influence was seen on the maternal blood pressure.19 However, pregnant women should be recommended to avoid high salt contents of the processed ready food.
 
 
Iron
The hemoglobin concentration declines when hemodilution occurs during pregnancy. Increased iron intake can prevent this decline. According to IOM, the future mother needs an average of 1000 mg iron in the last two trimesters of pregnancy in order to increase the maternal erytrocyte volume and the fetal erythropoiesis. In case no iron is supplied, deposition of the iron (ferritin) is consumed between weeks 12 and 25 in most of the pregnants in order to increase the eryrthrocyte volume.20 Maternal anemia, also, declines the fetal iron depositions. Anemia has negative effects on the fetal development, therefore maternal anemia must be prevented and treated.
IOM recommends that all pregnant women should be given elementary iron 30 mg/day during the second and third trimesters in order to avoid any iron deficiency anemia during pregnancy. Recommended dose for pregnant women with anemia is 60-120 mg/day. The risk for anemia is described as follows; hemoglobin being under 11 gr and hematocrite under 33% during the first and third trimesters, and hemoglobin being under 10.5 gr and hematocrite under 32% during the second trimester. 15 mg zinc and 2 mg copper supplements should be included in the diet of women taking theraupetic doses since the iron interferes with the absorption of those minerals. Due to the slight increase in the iron needs during the first 16 weeks of gestation, no supplement for iron is required in the first four months. Also, iron treatment given during the first trimester has aggravating effect on nausea and vomitting during pregnancy. In case the Hb is less than 11 gr, which is assessed at gestational weeks of 22-24 under normal conditions, prophylactic iron preparation can be used.
Furthermore, all pregnant women should be encouraged to eat foods rich in iron (chicken, fish, leafy vegetables, whole wheat bread, enriched bread and cereals), and they should also be informed that animal protein and ascorbic acide supplements enhance the absorption of iron. Tea and coffee shouldn't be consumed immediately after the meals. Excessive consumption of calcium and magnesium salts decrease the absorption of iron.
 
Calcium
Results on the role of calcium intake in preventing or treating the preeclampsia is highy controversial, and no sufficient data is available yet. Daily calcium requirement of women aged 19 to 50 years is 1000 mg/day while it is 1300 mg/day for those aged under 18.21 It has also been shown that calcium requirements during pregnancy are similar to those in the nonpregnant state.22 Daily consumption of three portions of food rich in calcium is sufficient to meet the daily requirements . Lower intake of calcium means an intake of 600mg/day (i.e., only one portion consumption of calcium-rich food and non-consumption of dairy products).
 
Folate
Folate is essential in the nucleic acid synthesis, and plays an important role in increasing the erythrocyte volume and meeting the requirements of growing uterus, placenta and fetus. Insufficient intake by diet and maternal genetic factors result in lower folate levels. In populations with poor gestational outcomes, it has been observed that micronutrients like folate are not consumed much. Smoking, alcohol intake and long-term use of oral contraceptives decrease the maternal folate levels, which are associated with increased risk of preterm delivery and fetal growth restriction.
Foods like strawberry, brocoli and leafy vegetables are rich in folate.
 
Zinc    
Zinc has a significant role in biochemical reactions. Therefore, adequate zinc levels are required for sufficient development and growth. Although some studies showed that lower maternal zinc levels may result in poor gestational outcomes, absence of a biochemical indicator showing the zinc levels prevents efficiency of studies. Zinc absorption may be declined in pregnants with higher dose of iron intake and gastrointestinal disease, smokers and alcoholics; in such cases, zinc supplement may be given.
 
Flourine
In a randomized controlled study, protective role of prenatal fluorine supplement on the tooth decay couldn't be shown with a follow-up up to 5 years of age. Consequently, fluorine supplement during pregnancy is still a controversial subject.23
 
Multi-Vitamin Supplement
During Pregnancy
Daily amounts of energy, protein, vitamin and minerals required for non-pregnant women aged 19 to 50, as well as pregnant and breastfeeding women have been announced by a bulletin (Recommended Daily Allowances (RDA) published in 1989 by the National Research Council Food and Nutrition Board in the U.S.7 Recommended amounts are not for personal needs, they only serve to guide as a social basis because nutrient requirements may vary from person to person. Use of prenatal vitamin and mineral preparations may make one person to consume some of the nutrients over the recommended amounts (RAD). Particularly, high doses of iron, zinc, selenium, vitamins A, B6, C and D may cause some toxic effects. In a study by Rothman et al. on 20,000 pregnant women, intake of Vitamin A exceeding 15,000IU/day was closely associated with birth defects.24 Also, failure to adjust blood glucose levels in diabetic patients, and blood phenylalanine levels in women with phenylketonuria during periconceptionel period results in poor gestational outcomes.(25-26)
American Academy of Pediatrics and ACOG indicate that recommended RDA doses should not be exceeded more than two-fold during pregnancy, and they don't encourage routine multivitamin supplement.28 In 1990, the Institute of Medicine stated that all vitamin and mineral requirements, except iron, during pregnancy can be met by a balanced diet, and routine vitamin supplement, except iron, is unnecessary. After that, U.S. Centers for Disease Control and Prevention recommended that all women of childbearing age with a potential to give birth should use 0.4 mg folic acide per day, following the introduction of the fact that periconceptional folic acide supplement reduced the occurence of neural tube defects half and half.29 Also, it has been recommended that the supplement should be 4 gr in women who have previously delivered an infant with a neural tube defect.30 Further studies are needed to reveal if the preconceptional intake of other vitamins is effective in reducing some other birth defect.(31 )Evidence from observational studies indicates that multivitamin-mineral supplement used before conception and during pregnancy reduces birth defects and poor gestational outcomes. Some observational studies showed that vitamin-mineral supplement initiated during first or second trimester resulted in a two-fold reduction in the risk for preterm delivery and possibility of lower birth weight.(32)
Although amount of scientific evidence revealing that routine vitamin supplement improves gestational outcomes is insufficient, it has been already shown that multivitamin-mineral supplement significantly reduced the preterm delivery and number of lower birth weight infants in adolescent pregnancies with severe insufficient nutrition.(32)
The Institute of Medicine and ACOG declared that routine vitamin supplement during pregnancy is unnecessary. However, both institutions stated that daily dietary habits of each pregnant woman should be evaluated, and a multivitamin supplement should be given at the beginning of the second trimester in case of insufficient food intake and inclusion in high-risk category (Table 3).9 Furthermore, vegan pregnants with low calcium intake should be supplemented by nutrients recommended by IOM as shown at Table 4.
In a study by Siega-Riz in 2002 on pregnant women in the North Carolina, it has been revealed that recommended iron intake only by diet has been met only in 30% while folate intake only in 60% of pregnant women.33 This shows that American women, even they have high income levels, cannot meet their nutritional requirements only by food, and a significant portion of pregnant women needs to be supplemented by multivitamins. However, compliance studies displayed that approximately 1/3 of pregnant women didn't take their prescribed multivitamins. It was found out that younger women with low education levels used multivitamins less.(34)
In conclusion, it should be clearly highlighted that multivitamin preparations meet only a part of the required nutrients, not all of them, even when the pregnant women are given multivitamin supplement; and they can never replace a healthy diet. Pregnant women should be advised about balanced and multi-nutrition, and their eating habits should be evaluated. All pregnant women should be given folate supplement during periconceptional/early pregnancy period. All nutrients with increased requirement during pregnancy except iron and folate can be met by diet, raising the consciousness about balanced diet (if the patient has no nutritional risk factor).
 
Exercise During Pregnancy
Excessive weight gain during pregnancy and being unable to loose that excessive weight at postpartum 6 months results in long-term obesity.36 Exercise and balanced diet ensure weight gain recommended during pregnancy. Exercise during pregnancy reduces risk for gestational diabetes and long-term obesity, and provides background for a faster labor and more rapid improvement, increasing posture, muscle tone, strenght and endurance.37 Exercise is also good for lumbago, gas, and swelling at foot, which are among the most frequent complaints of pregnancy.38 However, pregnant women should take an extra calorie of 300 kkal/day when practising exercise.39 Approach to exercise during pregnancy have been changing within years. In 1985, ACOG recommended to practise aerobic exercises not exceeding 15 minutes, and the heart rate to be at 140 at m/min.40 And, ten years laterthe same committee stated that women with uncomplicated pregnancy can have similar exercise level with non-pregnant women.(41)
 
Physiological Effects and Adaptations
Cardiovascular System
Cardiac output increases by 50%, and heart beats 15 times more than the resting heart rate, and blood volume rises 45%. Due to the increased capacity of veins, blood pressure declines, vasodilation occurs at the skin and tendency to hyperthermia is reduced as a result of heat loss.(42)It has been suspected that increased blood flow diverted to the muscles during the exercise may cause less blood pumping to the uteroplacental unit. However, compensatory changes caused by exercise such as increase in the maternal hematocrite and oxygen extraction help maintenance of the fetal oxygenation.43 Fetal heart rate increases by 5-15 beats for a short period of time, and does'nt impose any risk for the fetus. Unless an obstetrics or medical complication arises, no episodes of fetal brachycardia occur.44 However, supine position should be avoided after the first trimester since this position reduces the maternal cardiac output. Also, it has been shown that the uterine blood flow declines in women living in upland regions.45 It is recommended that women living in heights exceeding 2500 meters should avoid physical activities at least until 4-5 days are completed.(46,47)
 
Metabolic
It is known that maternal core temperature exceeding 39.2 degrees have potential teratogenic effects during the first trimester.48 Increased ventilation and skin blood flow are the adaptive changes protecting from hyperthermia during pregnancy.49 Yet, adequate hydration should be provided and exercising in very hot/humid ambiances should be avoided as precautions.41
Due to the restricted expansion of the diaphragm and increased needs of fetal oxygen during pregnancy, the VO2 max significantly declines during the exercise compared to the non-pregnant state.44 Consequently, carbonhydrates are used more (as shown by indirect caloriemeter). Thus, in extended (>45 min) or more exerted exercises, plasma glucose concentrations are significantly reduced. Therefore, during exercise, sufficient calorie intake and exercising time not exceeding 45 minutes should be recommended in order to minimise the risk for hypoglisemia.
 
Musculoskeletal Sytem
Changes related to the musculoskeletal system of the pregnant women increase the risk of injury during exercise. As growing breasts, uterus and fetus increase the lumbar lordosis, center of gravity shifts forward and increased weight contributes to the back; hormonal changes lead to increased laxity and mobility in the joints.51 Based on these, all exercises during pregnancy should be performed moderately and without weight bearing on the joints.
 
Effect on Fetus
Birth Weight
The information on the fetal birth weight of exercising women is contradictory. In a study by Clapp JF in 1990, it was shown that birth weight was significantly reduced when the pregnant women increased their activity level over 50% compared to their activity level before conception. In another study by Sternfeld, no difference was found between birth weights when exercising and sedentary pregnant women were compared. In a prospective study on 800 pregnant women by Hatch et al., the pregnant women who exercise with a total calorie expenditure of 2000 per week delivered infants with higher birth weight compared to the non-exercising women.53 A study by Pivarnik in 1998 concluded that:" Available data shows that moderate-intensity physical activities performed throughout the pregnancy may have beneficial effects on the birth weight", however, it should be kept in mind that heavy exercise schedules may result in lower birth weights.(54)
 
 
Duration of Pregnancy
It has been suggested that increased secretion of norepinephrine and prostaglandine during the exercise may activate the uterine and stimulate a premature delivery. However, number of studies related to this subject is very restricted. A study by Hatch carried out in 1998 reported that there was a reduction in the risk for preterm delivery, comparing 876 pregnant women with an energy expenditure of over 1000 kkal per week by aerobic activity with a group of non-exercising women. Therefore, it was concluded that exercising during pregnancy is safe.
 
Effect on Mother
Course of Pregnancy
It was observed that symptoms like nausea, fatigueness and lumbago are reduced in exercising pregnant women. In an observational study on 398 pregnant women, an inverse association was found between exercise and symptoms.
 
Labor and Delivery
The effect of exercise on labor is unclear. Many women indicated that they felt more energetic associated with exercise, and thus labor was easier. In an uncontrolled and non-randomized study, it was found that the delivery period was shortened in exercising women compared to the non-exercising women. In a study by Pomerance in 1974, it was observed that exercising multiparous women had shorther delivery period; but, this effect was not found in primiparous women. However, some other studies found no correlation between exercise level and labor period.
 
Exercise and Gestational Diabetes Mellitus
(GDM)
American Diabetes Association (ADA) recommends exercise as a part of treatment in case euglycemia is not restored by diet in GDM. A randomized study by Jovanovic in 1989 compared patients who used diet alone with patients who did aerobic arm exercise. And, at the end of week 6, levels of hemoglobin A1c, fasting plasma glucose, and satiety blood glucose were reduced in the exercising group, while no improvement occurred among the controls. Another study by Bung et al in 1991 used an exercise schedule with higher output and achieved normoglycemia at week 1.
 
Overall Recommendations
on Exercise
Pregnant women who previously have a sedentary lifestyle should be encouraged to start exercising. As a start, sports with low injury risk like walking and swmming not exceeding 20-30 minutes daily can be recommended while pregnant women who have been already exercising are recommended to unchange their schedule.
During exercises, following precautions should be taken:
1. Training schedule should have a regular basis.
2. Exercise should be stopped when deoxygenation symptoms like excessive fatigue, dizziness, shortness of breath develop.
3. Exercise should be performed in cool ambiances, and dehydration should be avoided in order to prevent excessive heating.
4. Long lasting exercising in supine position should be avoided during the second and third trimesters.
5. Contact sports and diving should be avoided.
6. Calorie intake additionaly required for exercise must be strictly followed (mean 300 kkal/day)
The contraindications indicated by ACOG in 1994 are as follows:
1. Intrauterine growth retardation
2. Persistent vaginal bleeding
3. Incompetent cervix or cerclage placement
4. Preterm labor risks
5. Rupture of membranes
6. Hypertension triggered by pregnancy
7. Severe chronic medical diseases

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	File/Dsecription
	Table 1. Recommended weight gains and speed of weight gain based on the prenatal weight*
	Table 2. Recommended dietary allowances (RDA).**
	Table 3. Nutritional risk factors during pregnancy***
	Table 4. Recommended vitamin and mineral supplements by IOM***