During pregnancy the body experiences some of the most physiologically demanding changes ever experienced in human life (Hytten and Chamberlain 1991). Whilst the body adapts to some extent, namely by increasing nutrient absorption via the gut, there are additional dietary requirements for certain nutrients (Table 15.1).

Firstly, energy requirements are mostly unchanged during pregnancy with the exception of the third trimester. The Scientific Advisory Committee on Nutrition reviewed energy requirements for pregnancy, advising that is was not necessary to amend original recommendations of an increment of 0.8 MJ per day (around 200 kcal/day) in the last trimester. It was, however, further noted that women entering pregnancy who are overweight may not need this additional requirement, although data is currently insufficient to formalize this (SACN 2011) (Figure 15.1).

An additional 6 g of protein per day was originally advised by the UK Department of Health. However, Canadian research investigating specific protein requirements during the different stages of pregnancy suggests that protein requirements are higher than original estimations of 0.88 g per kg body weight per day. It is now thought that protein requirements during early and late pregnancy are around 1.22 and 1.52 g per kg body weight per day, respectively (Stephens et al. 2015).

The requirement for the micronutrient folate increases during pregnancy to prevent megaloblastic anaemia and reduce the risk of neural tube defects (NTDs) such as spina bifida (Department of Health 1991). It should be also considered that different modes of food preparation can influence the stability of folate and its bioavailability. This can range from 25 to 50% from foods, 85% from enriched foods, and 100% from supplements (Banjari et al. 2014). In view of this and the tendency towards low habitual intakes of dietary folate the Scientific Advisory Committee on Nutrition advise that women planning a pregnancy should supplement their diet with 400 µg/day of folic acid (5 mg/day for women with a previous pregnancy affected by NTD) prior to conception until the 12th week of pregnancy (SACN 2006).

Vitamin B12 is an essential part of one carbon metabolic pathways and is central to the stability of nucleic acids and methylation of DNA which regulates gene expression. An increasing body of evidence now suggests that low maternal vitamin B12 status (as often seen in vegetarians) may be also be associated with increased NTD risk, alongside low lean fetal mass, excess adiposity, increased insulin resistance, and impaired neurodevelopment in the offspring (Rush et al. 2014). Presently, there is no additional increment for vitamin B12 during pregnancy but women should aim to achieve basic targets of 1.5 µg/day (Table 15.1).

An increment of 100 µg/day of vitamin A is recommended throughout pregnancy to allow for the rapid growth of the fetus (Department of Health 1991). As well as being important in supporting the development of the fetal eyes it is thought that all‐trans retinoic acid (RA) is the form of vitamin A that helps to support embryonic development, which includes the development of the reproductive systems of the fetus in utero (Clagett‐Dame and Knutson 2011),

In the case of iron, extra maternal and fetal red blood cells are manufactured during pregnancy leading to an increased requirement for iron, yet the UK Reference Nutrient Intake (RNI) for iron does not increase due to enhanced absorption, cessation of menstruation, and mobilization of iron stores. The increased absorption of non‐haem iron in pregnancy does, however, increase the vitamin C RNI by 10 mg/day in the last trimester (Department of Health 1991). The risk of pregnancy anaemia, typically defined as blood haemoglobin below 10.5 g/dL can be exacerbated by medical conditions including uterine or placental bleeding, gastrointestinal bleeding, and peripartum blood loss. Subsequently, this can increase the risk of intrauterine growth retardation, prematurity, and peripartum blood transfusion (Breymann 2015).

During pregnancy, calcium is needed to support changes in muscle function, nerve transmission, skeletal development, blood coagulation, and cell membrane function. This demand is mostly met by enhanced absorption and through mobilization of maternal skeleton calcium stores (Hovdenak et al. 2012). Whilst women who begin pregnancy with adequate intake may not need additional calcium, women with suboptimal intakes, defined as <500 mg daily, may need additional amounts to meet both maternal and fetal bone requirements, otherwise the risk of bone loss during pregnancy is likely to be higher (Hacker et al. 2012).

Vitamin D requirements rise to sustain the increase of calcium absorption and utilization during pregnancy and lactation, hence the RNI becomes 10 µg/day (Department of Health, 1991

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