Nutrition is important during pregnancy as the mother needs to meet the demands of the growing foetus whilst maintaining optimal maternal nutritional status. There are general dietary guidelines, including the UK Eat Well Guide [1], the Australian Dietary Guidelines [2], and the US Dietary Guidelines [3], as well as recommendations from the International Federation of Gynaecology and Obstetrics (FIGO) and Royal College of Obstetricians and Gynaecologists (RCOG) [4], that support the consumption of a healthy, balanced diet throughout pregnancy and in the post-partum period. These recommendations provide the necessary energy and macro- and micronutrient intakes for both the mother and foetus. The United Kingdom (UK) Dietary Reference Values (DRVs) clearly outline recommended intakes for macro- and micronutrients for the general population as well as for pregnant women [5].

There are certain nutrients of relevance to pregnancy that must be obtained from the diet, and a notable example is folate, which is an essential nutrient and must be obtained through the diet as humans cannot synthesise folate. It is recognised that inadequate dietary folate intakes can lead to foetal neural tube defects (NTDs), such as Spina Bifida, and that supplementation of 4.mg/d of folate in the first trimester of pregnancy results in a 70% reduction in the incidence of NTDs, as shown by the landmark definitive MRC Vitamin Study [6]. Since this research, the actual dose of folate recommendation to prevent NTDs was lowered and is now 400 µg/d in the UK [5], 600 µg/d in Australia [7], and 520 µg/d, as proposed by the Harmonized Nutrient Reference Values for populations [8].

The quality of food intake is important to provide the necessary micronutrients for optimal health. Recommendations from assembled experts on the health benefits of consuming nutritious food before, during, and after pregnancy suggest eating better but not more [9]. A multi-national scoping review identified that vegetable intake during pregnancy falls below recommendations worldwide for women of all body weights and needs to be addressed [10]. It was estimated that pregnant women consume approximately 27% of their energy from ultra-processed foods (UPFs) determined by the NOVA classification. This is similar to the general population, although women with obesity pre-pregnancy with the lowest blood haemoglobin levels were reported to have significantly higher intakes from UPFs compared to normal weight women [11]. This difference in UPF consumption may contribute to differences in macro- and micronutrient intakes in pregnant women of varying degrees of adiposity. General dietary advice is provided during the course of antenatal care [12] but is often not specific to the overweight/obese population. Guidance on the management of overweight/obese pregnancies [13] highlighted the need for advising women about the importance of a healthy diet and exercise during pregnancy in order to avoid excessive weight gain and gestational diabetes mellitus. The only specific nutritional guidance for overweight/obese woman regarded the increased supplementation of folic acid and vitamin D (5mg and 10 µg daily, respectively) and did not discuss other aspects including fat and complex carbohydrate consumption.

Maternal dietary intake can have a marked effect on the growing foetus and the newborn. A review by Hovedenak and Haram [14] described the impact of vitamin and mineral deficiencies on pregnancy outcomes. Examples include maternal iron deficiency that resulted in reduced neonatal iron stores and birth weight, and vitamin D supplementation in women with vitamin D deficiency in the third trimester, which was shown to be safe up to 4000 IU [15], improving vitamin D and calcium status, and thereby protecting skeletal health [16]. In the Healthy Start Study [17], 1410 pregnant girls and women (aged 16 years and older, and less than 24 weeks of gestation) were recruited from the University of Colorado Hospital (USA). The study reported that higher maternal intake of total fat, saturated fat, unsaturated fat, and total carbohydrate, but not protein, was associated with increased neonatal adiposity [18]. A further study showed associations of higher maternal intake of total fat, saturated fat, and excessive added sugar with increased infant percent body fat at 6 months [19]. There was a recent systematic review and meta-analysis of macronutrient and energy intake during pregnancy, which included 135,566 pregnant women from America, Eastern Mediterranean, Western Pacific region, Europe, and Southeast Asia and it showed that the mean intakes from energy, carbohydrate, fat, and protein were 2036kcal/day (8519kJ/day), 262g/day, 74g/day, and 78g/day, respectively [20]. However, there is limited evidence on micronutrient intake in pregnant women, with one study reporting low intakes in overweight/obese pregnant women [21], although the study lacked a comparator healthy weight control group. Hence, there is a scarcity of research that reports the dietary intakes of micronutrients in pregnant women of varying levels of pre-pregnancy weight status.

The energy intakes from fat and carbohydrate but not protein in the Scottish women were slightly higher than the mean of the 54 studies reported in the meta-analysis of maternal macronutrient and energy intake during pregnancy [20], but there were no significant differences in energy and macronutrient intakes between the overweight/obese and lean pregnant women groups in the current study.

The increased sodium intakes and sodium to potassium ratio in the overweight/obese women compared to the lean group would suggest that the overweight/obese women consumed more processed foods [28] and less unprocessed, wholesome foods, like fruit and vegetables, given that there is a correlation between potassium intakes and fruit and vegetable intakes [29]. However, in this study, there were no differences in the intakes of sodium-rich foods and fruit and vegetable intake between the two groups, likely due to the small sample size.

Micronutrients, such as niacin, folate, and vitamin D, were consumed in very low amounts and more than 87%, 95%, and 95% of women did not meet the H-AR for niacin, folate, and vitamin D, respectively, from diet alone. Furthermore, >76% of women from the lean group and >55% of women from the overweight/obese group did not meet the H-AR for vitamin E and magnesium, respectively. This shows that a large proportion of pregnant women are not meeting micronutrient intakes required for optimal health. Other studies have reported similar/mixed results. In Saudi Arabia, the vitamin D intake was 40 IU (approximately 2 µg per day) in pregnant women [30], which was much lower than the current study. Iron intakes in the USA were 14.4 mg per day [18] and 18.7 mg per day in Uganda [31], which were both higher than the current study. Folate intakes were very low in Uganda, ranging from 121 to 310 µg per day, which translated to 0–7% of pregnant women meeting the 600 µg per day recommended intakes [31], whereas folate intake (dietary intake alone) was 432 µg per day in the USA [18], which was higher than the current study, most likely due to folate enrichment of flour in the USA since 1996 [32]. Calcium intake in the USA was 1033 mg per day [18], similar to the current study, but calcium intake in China was only 602 mg per day [33], likely due to low milk consumption (China’s consumption is ranked at 137 out of 177 countries compared to the UK being ranked at 24) with actual consumption being 333 kg/capita/year in 2013 compared to 232 kg/capita per year in the UK in 2013 (https://en.wikipedia.org/wiki/List_of_countries_by_milk_consumption_per_capita, accessed on 18 December 2024). Calcium intake was also low in Uganda, ranging from 312 to 1018 mg per day depending on region and whether during planting or harvesting season [31] and this translated to 0–55% of pregnant women meeting the recommended intakes of 1000 mg per day for calcium. Iron intakes in Uganda ranged from 9.9 to 22.4 mg per day, resulting in 0–55% of pregnant women meeting the recommended intakes of 27 mg per day, whereas iron intake in the USA [18] and China [33] was 14.4 and 18.7 mg per day, respectively, which were higher than the current study. Collectively, these few studies on micronutrient intakes during pregnancy highlight that some micronutrient intakes do not meet the recommended dietary intakes for pregnant women, which may have detrimental consequences for the growing foetus.

Folate is essential for the prevention of NTDs, as shown by the definitive MRC study [6], and several other micronutrients, including niacin, are associated with a reduced risk of NTDs [34]. Less than 5% of pregnant women met the 520 µg H-AR for folate during pregnancy through diet alone; hence, many women relied on folate supplementation to meet the H-AR. Green leafy vegetables are a rich source of dietary folate, but it was reported that pregnant women have low vegetable intake [10]. Unlike folate, niacin is not an essential nutrient as humans can synthesise niacin from the amino acid tryptophan, where it is estimated that 60 mg of dietary tryptophan is equivalent to 1 mg niacin [35].

Vitamin D helps to maintain muscle and bone strength and helps the body to absorb calcium from food. In pregnancy, vitamin D also aids bone development and the amount of calcium within the baby’s bones can be affected by a vitamin D deficiency in the mother. For this reason, there are specific recommendations for vitamin D supplementation during pregnancy [36]. Vitamin D supplementation was shown to be safe up to 4000 IU and is largely devoid of any adverse pregnancy outcomes [15]. Moreover, it was shown that maternal vitamin D intake affects postnatal growth and is inversely associated with childhood overweight in children of mothers with normal weight [37], highlighting the importance of pre-pregnancy weight status in addition to its association with diet quality [38]. Vitamin D can be synthesised by the body through sunlight exposure and 9 minutes of daily exposure to sunlight will maintain vitamin D status in the UK through their winter [39], but this is dependent on sunlight.

Vitamin E was found to be very effective in the prevention and reversal of various disease complications due to its function as an antioxidant, its role in anti-inflammatory processes, its inhibition of platelet aggregation, and its immune-enhancing activity [40]. Vitamin E intake was associated with several health benefits (coronary heart disease, cancer, eye disorders, and cognitive decline); however, supplementing the diet with vitamin E is not supported by scientific evidence [40] and at present, there is no UK recommended intake for pregnant women.

Additionally, iron is needed for erythrocyte synthesis to support an increase in blood volume during pregnancy and to prevent anaemia. The WHO key facts state that globally 37% of pregnant women are affected by anaemia [41]. Therefore, pregnant women who are micronutrient deficient during pregnancy are putting themselves and their babies at risk of suboptimal health and birth defects.

There are plenty of resources for nutrition advice in pregnancy including from the UK [1,42], Australia [43] and the USA [9]. Nevertheless, given the current results, there is a need for health care providers to provide a simple message such as to ‘eat better and not more’ [9], as well as specific advice on foods that are rich in niacin, folate, vitamin D, and vitamin E. Therefore, the advice should recommend the consumption of fish (preferably oily), meats (including lean red meat and chicken/turkey breast meat), and unprocessed foods including green leafy vegetables, legumes (including peas and beans), and nuts, as well as providing specific advice to refrain from consuming foods rich in salt, including ultra-processed foods. An example of such a diet is the Mediterranean diet, which provides numerous health benefits including improved cardiovascular health [44].