Optimal outcomes of pregnancy and their importance to the mother, the future child, families and societies, is contingent on appropriate care, adequate antenatal preparation and sufficient nutrition. The consequences of antenatal nutritional deficiencies can be devastating to the mother, child and affect future generations.
As such, it is critical that expectant mothers enter pregnancy with the best possible macronutrient and micronutrient status and then receive adequate antenatal nutrition for their health, and for the well-being of their offspring.
Maternal nutrition has profound effects on foetal growth, development, and subsequent infant birthweight, and the health and well-being of the woman herself.
Maternal undernutrition, maternal mortality rates, infant mortality and morbidity rates have declined since the 1990s as a result of increasing attention to improving the quality of the antenatal period and improving obstetric care and social change.
However, there is still a great need for further improvements. The nutritional status and size of the pregnant woman is the result of past health and nutrition, including her own birth size and subsequent health and societal influences.
Poor dietary patterns, and options, in the periconceptional period are known to lead to preterm delivery, shorter birth-length, earlier gestation and poor potential neurodevelopmental outcomes for the foetus.
Given the impact of poor maternal diet, both public health and clinical measures need to be in place, especially in low socio-economic environments. These need to address all stages of a woman’s life-cycle, and especially during the pregnancy.
Nutritional, dietary and health interventions need to be complemented by improved obstetric care and support, and exposure to ‘nutrition-sensitive’ interventions such as access to education, improvement in women’s status and improved agricultural and environmental determinants.
While the global burden of diseases caused by deficiencies of micronutrients during pregnancy is relatively modest globally, the cumulative individual impact can be considerable. This is especially so for adolescent pregnancies and women of lower economic or minority status in low and middle-income economic settings.
Globally, approximately two billion people, the majority of them being women and young children, are affected by micronutrient deficiencies, with even higher rates during pregnancy.
Concurrent deficiencies of more than one or two micronutrients are well documented among young pregnant women (and young children), especially in low and middle-income countries (LMIC).
Deficiencies in maternal micronutrient status are a result of: poor quality diets; high fertility rates; repeated pregnancies; short inter-pregnancy intervals; and, increased physiological needs.
These factors are aggravated by often inadequate health systems with poor capacity, poverty and inequities, and socio-cultural factors such as early marriage and adolescent pregnancies, and some traditional dietary practices.
Pregnancy during adolescence is a relatively common event in much of the world and the young women are usually incomplete in their own growth and often deficient in micronutrients. Pregnancies at this time will make reproductive outcomes more likely to be negative as well as adversely affecting the health, nutrition and well-being of the adolescent.
In countries including the UK, studies of micronutrient status in adolescents, including those pregnant, have found poor micronutrient intakes and status, and increased risk of small-for-gestational-age (SGA) and low birthweight (LBW) infants at birth.
Besides negatively affecting the young mother’s own growth and nutritional status, adolescent pregnancy is also associated with a 50 percent increased risk of stillbirths and neonatal deaths, and increased risks of preterm birth, low birthweight, and asphyxia.
A review assessing the association between inter-pregnancy intervals with maternal, newborn, and child health outcomes found that short inter-pregnancy intervals (60 months) were associated with an increased risk of pre-eclampsia.
Dutch Famine Of 1944
The effects of micronutrient deficiencies on their offspring also need to be addressed as part of the mother-child dyad. Perhaps the most noteworthy natural experiment demonstrating this necessity came about as a result of the Dutch famine of 1944 which provided a unique opportunity to study the long term consequences of maternal nutritional status and health outcomes in offspring.
Before the famine ended in 1945, rations were as low as 500 Kcal per person. Expectant mothers who were subjected to the famine became severely macro- and micronutrient deficient.
The famine was directly observed to affect fertility, infant birth weight, maternal weight gain, and the development of the neonate’s central nervous system.
Assessing the impact of antenatal micronutrient status of pregnant women (especially when improved by supplementation) on the outcomes for their offspring is a challenge due to the need to follow the women through pregnancy and then the offspring as they grow, and often in less than ideal settings for such research.
In an important study from Nepal, intellectual functioning, including working memory, inhibitory control, and fine motor functioning among offspring at seven to nine years of age were positively associated with prenatal iron/folic acid supplementation in an area of high iron deficiency.
Related and similar findings of positive impact on the child of maternal antenatal supplementation have been found in Bangladesh, China and Tanzania. A study from rural Vietnam found that low maternal 25-hydroxyvitamin D levels in late pregnancy were associated with reduced language developmental outcomes at six months of age.
Maternal antenatal zinc supplementation may have beneficial long-term consequences for neural development associated with autonomic regulation of cardiovascular function in children at 54 months whose zinc-deficient pregnant mothers had received supplementation.
Even in areas of mild-to-moderate iodine deficiency, subtle reductions in the intelligent quotient of children in those areas may be reduced on average by 8–13.5 IQ points but can be corrected in populations by salt iodisation.
On the other hand, there is increasing evidence of a positive impact of multiple micronutrient supplementation to deficient mothers on the growth and development of their offspring, although mechanisms are still unclear and findings inconsistent. This is probably because of different formulations and dosages of the supplements, rather than lack of effect.
Food supplementation, especially in emergency and resource-poor settings, is increasingly evidence-based. Emergency rations and supplies in particular have invested considerable resources in ensuring that the micronutrient content of such supplements are adequate while recognising that in undernourished pregnant mothers it is the low energy (caloric) content of the available diets that is the main risk.
The MINIMat randomised trial in Bangladesh found that among these pregnant women from poor communities, supplementation with multiple micronutrients, as well as just iron and folic acid, combined with food supplementation, resulted in decreased childhood mortality.
A recent review concluded that a dietary pattern containing several protein-rich food sources, fruit, and some whole grains is associated with a reduced risk of preterm delivery.
A platform used with limited experience (in pregnant women) has been the use of multi-micronutrient powders (added to food) during the antenatal period, or more recently lipid-based supplements that supplies dietary energy, protein and micronutrients.
Studies show that use of micronutrient fortified supplementary foods, especially those containing milk and/or essential fatty acids during pregnancy, increase mean birthweight by around 60–73 g. Fortified food supplements containing milk and essential fatty acids, along with micronutrients, offer benefits for improving maternal status and pregnancy outcome.
Fortified beverages containing only multiple micronutrients have been shown to reduce micronutrient deficiencies such as anaemia and iron deficiency. Food supplementation, while clearly effective in undernourished mothers will not be discussed further here, as it is mainly an intervention to increase dietary energy and the micronutrients needed to accompany it are largely known.
Other interventions that impact on the micronutrient status during pregnancy include dietary measures and other public health and social interventions such as deworming, education and horticultural activities.
While the risk of low birthweight is significantly greater with moderate preconception anaemia, it has also been noted that in many unsafe settings, mothers purposefully ‘eat-down’ aiming to have a smaller neonate. A failure of nutrition education has also been implicated in poor diets as well as some dietary taboos and soil-transmitted helminths.
Nevertheless, where access and availability to foods is possible, diets can be improved by including items such as eggs and animal-source foods to provide protein, energy and micronutrients. However, these are often not available to the very poor, or places with cultural constraints, which is why food supplements to these pregnant women is now a recommendation.
International guidelines recommend routine safe and protective prevention and treatments, during pregnancy, to reduce hookworm, malaria and other infections such as schistosomiasis.
Despite the effectiveness of such programs, and because women with high levels of hookworm or malaria infections are at high risk of anaemia, there continues to be a need for more general scaling-up of coverage in affected populations.
A recent randomised trial (that included pregnant women with anaemia and iron deficiency at baseline) in a malaria endemic area found major gains in birthweight, without apparent effect on plasmodium infection. The study urged that universal coverage of iron supplementation (60 mg per day) should be scaled up, preferably with cover by intermittent preventive treatment (IPT) of malaria.
Attention to adolescent girls as an important preventive strategy is increasingly recognised, despite some strong cultural and social constraints.
It has been observed that, even in affluent settings, adolescents are more likely than adults to consume energy-dense, micronutrient-poor diets and to have adverse pregnancy outcomes such as increased risk of SGA. The risk is likely to be even greater in food-insecure populations such as in Central Africa.
Other non-direct micronutrient interventions that could be expected to have a positive impact on nutrition and health of pregnant women (at least where most births are within a marital relationship), include interventions to increase the age at marriage and first pregnancy, which are important as they can reduce repeat adolescent pregnancies by 37 percent.
Fortification can be considered a dietary intervention and has been in practice for over sixty years in many affluent countries. It has been previously concluded that fortification has the greatest potential to improve the nutritional status of a population when implemented within a comprehensive nutrition strategy. This also applies to pregnant women and has the advantage of reaching women before pregnancy.
Iodised salt programs are now implemented in many countries worldwide, and have shown considerable progress in the past two decades. Globally, 76 percent of households are now adequately consuming iodised salt.
However, nearly 30 percent of school-aged children are estimated to have insufficient iodine intakes and global progress appears to be slowing. The need for continual global scaling-up and consolidation of existing programmes has already been commented upon. There have also been efficacy, and limited effectiveness studies of doubly fortified salt with iodine and encapsulated iron.
The provision of balanced energy protein supplementary foods to underweight pregnant women was also considered to have enough evidence of reduction in SGA and stillbirths and improved birthweights for widespread implementation, whereas maternal vitamin D and zinc supplementation, while promising, were considered to have insufficient evidence.
Fortification of cereal flours with iron and often other micronutrients such as some B group vitamins, and more recently zinc and even selenium, has been in existence for over 60 years, and now 80 countries globally have legislation to mandate fortification of at least one industrially milled cereal grain (79 countries have legislation to fortify wheat flour; 12 countries to fortify maize products; and five countries to fortify rice).
Currently, the 79 countries that mandate required fortification of wheat flour produced in industrial mills require at least iron and folic acid, except Australia, which does not include iron, and Congo, the Philippines, Venezuela, and the UK, which do not include folic acid.
Additionally, seven countries fortify at least half their industrially milled wheat flour through voluntary efforts and it has been estimated that about a third (31 percent) of the world’s industrially milled wheat flour is now fortified with at least iron or folic acid through these mandatory and voluntary efforts.
Other success stories include the fortification of sugar with vitamin A in Central America. A continuing challenge is that populations most at risk of deficiency either cannot afford fortified foods or, especially in lower-income countries, they are not available to them. Nevertheless, fortification is likely to be an increasingly major part of the reduction of micronutrient deficiencies, including during pregnancy.
Most Neglected Aspect
Maternal undernutrition has been described as one of the most neglected aspects of nutrition in public health globally. Consequently, low-cost public health interventions that might help to ameliorate the impact of poor nutrition and diets, high disease burdens and the socio-cultural factors contributing to the high levels of these micronutrient deficiency problems before and during pregnancy, continue to need scaling-up in scope and coverage.
Important factors besides inadequate diet and diseases that are indirectly related to maternal, foetal, and neonatal nutritional status and pregnancy outcomes include young age at first pregnancy and repeated pregnancies.
Young girls who are not physically mature often enter pregnancy with depleted nutrition reserves, anaemia and other micronutrient deficiencies. While micronutrient deficiencies can undoubtedly have profound influences on the health of the mother and her child, there remain considerable areas of uncertainty and controversy that has made the development of robust public health recommendations a challenge.
Along with the noted challenges to get compliance, especially periconceptionally and in settings with limited health care capacity, are questions of how optimal micronutrient formulations and dosages are established.
However, the methodological issues in doing this would be considerable, especially in establishing causality. Consequently, factors that are known to be important, such as entering a pregnancy adequately nourished, being aged beyond adolescence, having good health and obstetric care, and nutrition education and support, should be scaled-up actively in the meantime.
If proven to be effective and safe in national health care systems, supplementation with multi-micronutrients, at least in pregnancy, could complement preventive supplementation with weekly iron and folic acid in vulnerable populations.
This could help break the intergenerational reality of low birthweight infants growing up disadvantaged and stunted and so at high-risk of repeating the same cycle. While there has been a lot, if insufficient, attention paid to iron deficiency anaemia in pregnant women, for most of the other involved micronutrients, they are still not as well-characterised.
Micronutrients likely to be important for maternal, infant and child outcomes include iron, iodine, folate, vitamin B12, vitamin D, calcium, and selenium, probably zinc and maybe others, along with appropriate dietary energy intakes.
In addition to programs to reduce micronutrient deficiencies such as micronutrient supplementation and food fortification, complementary interventions should improve overall maternal nutrition, address household food insecurity, reduce the burden of maternal infections such as HIV and malaria, improve sanitation, and actively address gender and social disadvantage.