To our knowledge, this is the first prospective cohort study to examine the relationship of maternal dietary diversity and nutritional adequacy in both pre- pregnancy and pregnancy condition with anthropometric measurements of infants at birth. In our study, there was no significant association between pre-pregnancy maternal DDS and infant anthropometric indices at birth, but after adjusting for maternal and the neonatal confounders, maternal DDS (in gestational stage) and MAR (in both stages of mother`s intake assessment) were negatively associated with Weight and BAZ.
Total DDS of mothers in pre-pregnancy and pregnancy states were 5.31 and 5.23, respectively. The pre-pregnancy score of the studied women was lower than the amount reported in a cross-sectional study in Tehranian women aged 18–80 years that the mean DDS was 6 (35). In two study in Bangladesh (36, 37)the mean women diet diversity score (WDDS) of participants who were in the reproductive age was 4.3 and 3.8, respectively that was lower than present study.
Dietary intake analysis of studied mothers in both state (pre-pregnancy and third trimester of pregnancy) showed that those with higher score for DDS had higher score for intake of all main component of DDS (bread and cereals, meats, dairy, vegetables and fruit groups). In one study that examined WDDS during pregnancy, women with highest total score obtained higher dairy, animal-source foods, and vitamin A rich fruits &vegetables scores than those with less total WDDS(16).
In this prospective cohort study, we observed that maternal DDS during pregnancy was negatively associated with weight, WAZ and BAZ in birth after adjusting for confounding factors. Consistent with this study, the results of a cohort study showed that adequate dietary diversity during pregnancy and greater consumption of dairy, fruits, vegetables, animal foods such as meat and eggs were associated with lower risk of low birth weight (LBW)(16). Another study showed that Individual Dietary Diversity Score (IDDS) had a significant inverse relationship with LBW incidence (OR = 0.43, P = 0.014)(10). Nonetheless, a randomized controlled trial in India showed that taking of more dairy products, fruits and vegetables before and during pregnancy through a specially formulated snack doesn’t affect birth weight(38). In another study WDDS of ≥ 4 food groups during pregnancy was associated with lower risk of maternal anemia, low birth weight (LBW), preterm birth (PTB)(16) .
In current study, beside maternal and neonatal confounders, adjusting socioeconomic status had an important role in significance of findings. A previous study confirmed that socioeconomic factors, especially household income and education, play a crucial role in women's dietary diversity and wealthy families and literate women had significantly higher dietary diversity scores(36).
The findings of the present study show that, despite high number of mothers were at the lowest tertile of pre-pregnancy DDS, their frequency at the third tertile was increased in pregnancy stage. Perhaps, one of the possible reasons for increasing the DDS of pregnant mothers was due to receive nutritional counseling from primary health centers/hospitals and increasing their sensitivity to follow the nutritional recommendations during this susceptible period. On the other hand, high percentage of newborns had birth weight in the normal range of 2500 to 4000 g that may be related to increasing mothers' dietary diversity in the third trimester of pregnancy and improving their weight gain resulted to a normal birth weight range of newborns. However, few studies have examined maternal dietary diversity during pregnancy and its association with neonatal anthropometric indices, and this needs further investigation in future studies
Generally dietary diversity improves the intake of micronutrients and leads to improved pregnancy outcomes. Particularly in the second trimester of pregnancy, oxidative stress is reached to the highest level and may lead to inflammation and effect on pregnancy outcomes. Obtaining higher dietary diversity score means that variety of antioxidant rich food groups are eaten that may protect against oxidative stress (16).
In the present study, there was no significant relationship between maternal nutritional adequacy before and during pregnancy with neonatal anthropometric measuresat birth. After adjusting for maternal and neonatal confounders, a reverse significant relationship was observed between maternal's nutritional adequacy whit birth weight and WAZ at birth. In a longitudinal cohort study conducted in Australia, women in the highest quartile of MAR had lower fat and saturated fatty acids and higher protein, carbohydrate, and fiber intake compared with women in the lowest quartile. However, there was not any information of their pre-pregnancy intake (39). In another study examining maternal nutritional adequacy during pregnancy based on RDA, some micronutrients such as vitamin C, vitamin A, potassium, iron and selenium levels were lower than recommended (40).
The present study showed that the average intake of iron, iodine, vitamin B6, vitamin E and vitamin D was lower than recommended dietary allowance (RDA) in pregnant women but the mean calcium intake was 1.4 times higher than RDA. In one study examining the nutrient intake of mothers during pregnancy, the findings showed that mothers had lower vitamin E, folate, magnesium, and iron intake than recommended DRI values(41). In the Australian study, high percentage of women receiving inadequate calcium, folate, magnesium, and potassium and vitamin E indicating lower nutrient intake than pre-pregnancy RDI. However, these studies did not examine the relationship between maternal nutritional adequacy and neonatal anthropometric indices. In addition, other large studies focusing on maternal nutritional adequacy during pregnancy have also examined only one single nutrient(42, 43). In a study aimed investigating the effect of pre-pregnancy BMI, energy and nutritional supplements on neonatal body composition, the portion of mother`s carbohydrate from total energy intake was positively related with infant adipose tissue(44).
It seems that high intake of calcium in present study may possibly be associated with reduced risk of overweight and obesity. Apparently, the mechanism of this effect is related to the reduction of PTH and 1, 25-Dihydroxyvitamin D which leads to inhibition of lipogenesis and increase lipolysis and ultimately increase in fecal fat excretion due to the formation of soaps(45). Perhaps this is a reason for the negative relationship seen in this study. However, this reverse association may be attributed to the fact that mothers with higher adequacy of the diet are at the normal range of weight that affects to gain weight at the normal range during gestation and to deliver a baby with normal birth weight.
The main strength of this study is the information was gathered in a prospective cohort and mothers were followed up during pregnancy until delivery. Also, in order to assess the nutritional status of the mothers, two dietary intake methods were used. 24-hour recalls as a gold standard method reflected actual intake of pregnancy stage and FFQ assessed the usual dietary intake of women before deciding to pregnancy. Dietary intake assessments have some limitations such as measurement error, misreporting of dietary intake specially under reporting for unhealthy items by obese mothers (46, 47).