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Maternal dietary diversity during pregnancy and risk of low birth weight in newborns: a systematic review
* and Associated Data
Abstract
Objective:
Maternal nutrition during pregnancy is a key factor influencing birth outcome. Dietary diversity is a proxy for multiple macro- and/or micronutrient sufficiency of an individual’s diet. This systematic review aimed to summarise the findings on the association between maternal dietary diversity during pregnancy and the risk of low birth weight (LBW) in newborns.
Design:
This is a systematic review study.
Setting:
Google and the PubMed, Scopus and Google Scholar databases were searched to extract original studies on humans published until June 2020, without date restrictions. There was no limitation regarding geographic region or economic condition of countries. Duplicated and irrelevant studies were screened out and data were obtained through critical analysis.
Participants:
Articles that examined the association between maternal dietary diversity during pregnancy and the risk of LBW in infants were included.
Results:
Of the ninety-eight studies retrieved, fifteen articles were included in the final review. All included articles represent low- and middle-income countries. Eighty percentage of the studies (n 12) indicated that low maternal dietary diversity during pregnancy is associated with an increased risk of LBW infants. Three studies that included a small number of LBW infants and did not take into account factors which may bias study results failed to show this association.
Conclusion:
The results suggest that low maternal dietary diversity during pregnancy may be associated with the risk of LBW, more specifically in developing countries. Dietary diversity might be a valuable predictor of maternal nutrition during pregnancy and the chance of giving birth to a LBW infant.
Newborn birth weight <2500 g, regardless of gestational age, is defined as low birth weight (LBW)(1), a condition that compromises infant growth(2) and cognitive development(3) and is strongly linked to infant mortality, morbidity(4) and chronic diseases later in life(5). Globally, it is estimated that 15–20 % of all births are LBW, corresponding to more than 20 million births per year(1). One of the WHO global nutrition targets is to reduce the number of LBW babies by 30 % between 2012 and 2025(1). At the population level, the proportion of LBW infants represents a multifarious public health problem. Known risk factors for LBW include preterm birth(6), intrauterine growth restriction(7), maternal factors such as young age(8), multiple pregnancies(9), poor nutrition(10), unfavourable work conditions(11), chronic disease(12), alcohol abuse(13), inadequate prenatal care(14) and environmental factors such as smoking(15), lead exposure(16) and air pollution(17).
Maternal nutrition during pregnancy is a key factor influencing birth outcomes. Pregnant women are at increased risk of various micronutrient deficiencies, particularly in developing countries(18,19). Besides, most LBW infants in these countries are full-term newborns with intrauterine growth restriction due to maternal malnutrition and poor gestational weight gain(20,21). Evidence also indicates that maternal malnutrition contributes to detrimental pregnancy outcomes(22,23), reduced newborn survival(23,24) and an increased risk of chronic diseases(19,25,26) and mental and cognitive impairment in later life(27,28). Consuming invariant and monotonous diets can cause micronutrient deficiencies, which subsequently impact fetal growth and, hence, increase the odds of LBW(29,30).
Dietary diversity is a qualitative measure of food intake that, in a snapshot form, addresses individual access to different types of foods(31). It is an indicator of nutrient adequacy of an individual’s diet and is a proxy for multiple macro- and/or micronutrient sufficiency of the diet(31). Different indicators are used for the assessment of dietary diversity. The Minimum Dietary Diversity for Women (MDD-W) and Women’s Dietary Diversity Score (WDDS) are most used tools adopted by the FAO(32). The tools advocated for use in women aged 15–49 years and validated against micronutrient adequacy assessed by multiple 24-h recalls(32). Based on food items consumed in the past 24 h, individuals are allocated the number of food groups they consumed, ranging from 0 to 9 (for WDDS) or 0 to10 (for MDD-W).
Numerous investigations have evaluated the association between maternal dietary diversity during pregnancy and LBW risk in offspring(33–41). However, there is still no comprehensive research summarising all of these reports. The research question was as follows: Is maternal dietary diversity associated with risk of LBW in newborns? Therefore, this systematic review was designed to systematically evaluate and summarise the literature in order to determine whether is there a relationship between maternal dietary diversity during pregnancy and the risk of LBW in newborns?
Methods
This systematic review was conducted following the Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines (2015 Statement)(42).
Search strategy
A literature search was conducted in the PubMed, Google Scholar and Scopus databases, as well as Google, until June 2020, with no date restrictions. The following keywords were employed in the search: ‘dietary diversity’ OR ‘diet diversity’ OR ‘food diversity’ OR ‘dietary variety’ OR ‘diet variety’ OR ‘food variety’ in title-abstract-keywords AND ‘birth weight’ in title-abstract-keywords. Limits were English language and original articles. Details on the search strategy used for PubMed, Google Scholar and Scopus databases are included in Table Table1.1. A manual search of the reference lists of the included articles was done to find further studies.
Table 1
Association between maternal dietary diversity and risk of low birth weight: method of the database search strategy using PubMed and SCOPUS
| Database | Search terms* |
|---|---|
| PubMed (search conducted up to 14 June 2020) | ((((((dietary diversity[Title/Abstract]) OR (diet diversity[Title/Abstract])) OR (food diversity[Title/Abstract])) OR (dietary variety[Title/Abstract])) OR (diet variety[Title/Abstract])) OR (food variety[Title/Abstract])) AND (birth weight[Title/Abstract]) |
| SCOPUS (search conducted up to 15 June 2020) | TITLE-ABS-KEY (‘dietary diversity’) OR TITLE-ABS-KEY (‘diet diversity’) OR TITLE-ABS-KEY (‘food diversity’) OR TITLE-ABS-KEY (‘dietary variety’) OR TITLE-ABS-KEY (‘diet variety’) OR TITLE-ABS-KEY (‘food variety’) AND TITLE-ABS-KEY (‘birth weight’) AND DOCTYPE (ar) |
| Google Scholar (search conducted up to 15 June 2020) | allintitle: ‘dietary diversity’ OR ‘diet diversity’ OR ‘food diversity’ OR ‘dietary variety’ OR ‘diet variety’ OR ‘food variety’ ‘birth weight’ with at least one of the words: ‘dietary diversity’ OR ‘diet diversity’ OR ‘food diversity’ OR ‘dietary variety’ OR ‘diet variety’ OR ‘food variety’ with the exact phrase: birth weight |
Eligibility criteria
Original articles published in English were included. There was no restriction regarding geographic region or economic condition of countries. Cohort, cross-sectional and case-control studies addressing the relationship between maternal dietary diversity and the risk of LWB in newborns were included. Studies referring to emergency conditions or natural disasters such as cyclones were excluded. Studies that assessed the relationship of dietary diversity with other health issues such as anaemia, diabetes or hypertension were excluded. Moreover, studies that investigated the effect of dietary patterns (e.g., Western, traditional, healthy and unhealthy patterns) during pregnancy on LBW were also excluded.
Selection of the studies
The extracted investigations were transferred to an Endnote file and arranged to remove duplicate articles. The titles and abstracts of the remaining articles were screened by two independent reviewers to identify articles potentially eligible for this review. The full texts of the screened studies were then critically reviewed separately for eligibility and data extraction. Any discrepancy in evaluation between the two reviewers was resolved through discussion.
Data extraction
The extracted data were as follows: first author and year of publication; country and study design; number of study population; maternal age and time of data collection; study location (urban or rural) and data collection location; method of dietary diversity assessment; duration of food intake information; number of food groups considered and cut-off point for inadequate dietary diversity; total number of LBW infants and number of LBW infants in low DDS group; covariates adjusted; findings accompanied by OR, CI or other indicators of correlation, P value, if available.
Quality assessment
Selected studies were assessed for methodologic quality by two independent reviewers. The Newcastle-Ottawa Quality Assessment tool for observational cohort and case-control studies(43) was used to evaluate the quality and risk of bias of the included studies based on three domains: the selection of exposed and non-exposed groups, ascertainment of exposure; the comparability of groups on the basis of the design or analysis controlled for confounders; and the outcome regarding assessment and follow-up time. A star system was applied to classify the articles as good, fair or poor quality. Studies with a total score of 6 or higher were classified as high quality.
Results
Selection of studies
As shown in Figure Figure1,1, ninety-four studies were first retrieved by the search strategy and four studies by manual searching. Duplicates were removed and sixty-four studies remained. Of those, twenty-three publications met the topic and scope of the study during the screening phase. During critical review, eight studies were excluded because they did not meet the eligibility criteria or were conducted under emergency conditions. Finally, fifteen articles were included in the review (Fig. (Fig.11).
Flow diagram of the literature search and screening process for a systematic review assessing the relationship of dietary diversity and risk of low birth weight
Characteristics of the included studies
As shown in Table Table2,2, all included studies were from low- and middle-income countries and were published between 2013 and 2020. All studies applied a cohort, cross-sectional or case-control design. In ten of the studies, dietary intake information was collected only over the prior 24 h. All studies were conducted in hospitals or health facilities. All but two studies(37,44) used FAO adopted instrument for the assessment of DDS(32). The time of data collection was after delivery in four of the included studies(34,36–38) and for the other studies it was in second and/or third trimesters(33,35,40,41,44,45,46) or between 34 and 36 weeks(39), first 8 weeks(47) and 9–15 weeks(48) of gestation. Several studies were conducted solely in urban areas (n 6). One of the studies was online Master’s theses(45). Various criteria or cut-off points were used to identify low DDS across the included studies. Low DDS ranged from <3 to ≤7, with most used cut-off of ≤3 or <5, across the studies.
Table 2
Summary and characteristics of the fifteen selected observational studies assessing the relationship of maternal dietary diversity and risk of low birth weight
| Author(s), year, reference | Country/type of study | Study population | Maternal age (year)/time of data collection | Study location (%)/data collection location | Method of DD assessment | Duration of food intake information | No. of food groups considered/inadequate DDiv | Total no. of LBW infants/no. of LBW infants in low DDS group | % | Covariates adjusted | Findings |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Abubakari and colleagues, 2016(33) | Ghana/cohort | 578 singleton pregnant women and their newborns | ≥ 15/second trimester followed until delivery | Urban: 78·20; rural: 21·8/hospital and child welfare clinics | FAO adopted women DDS using FFQ (analysis contained thirty-six food items) | Per week | 9/– | 162/– | 28·0 | Gestational age, women with regular antenatal care attendance and without severely ill state included | Mothers with high DDS had reduced risk of LBW infants (OR: 0·10; 95 % CI 0·04, 0·13; P < 0·0001) per sd change in scores |
| Ahmed and colleagues, 2018(34) | Ethiopia/case-control | 279 singleton live births (93 < 2500 g and 186 births ≥ 2500 g) and their mothers | LBW: 27·3 (sd 5·5) NBW: 26·2 (sd 4·7)/after given birth | Urban: 58·4;rural: 41·6/hospitals and health centres | FAO adopted MDD-W | Based on past 24-h recall | 10/MDD-W < 5 | 93/87 | 93·5 | Potential confounders were controlled Neonates with major congenital anomalies, diabetic mothers and mothers with unknown last menstrual period were excluded | 93·5 % of LBW and 62·9 % of NBW neonates were belonged to mothers with inadequate DDS (P < 0·0001) Mothers with inadequate DDS had about seven times higher odds of having LBW babies (OR: 6·65; 95 % CI 2·31, 19·16) |
| Alemu and Gashu, 2020(47) | Ethiopia/cohort | 341 pregnant women | 26·4 (sd 4·8)/first 8 weeks of pregnancy followed until delivery | Urban/antenatal care units | FAO adopted MDD-W | Based on past 24-h recall | 10/MDD-W < 5 | 44/– | 13·4 | Maternal age, parity, educational status, BMI, Fe, folic acid supplementation, serum Zn and Hb concentration | Low dietary diversity was not associated with LBW (crude OR: 1·2; 95 % CI 0·5, 2·5; P = 0·6) |
| Bekela and colleagues, 2020(49) | Ethiopia/case-control | 354 mother–neonate (118 LBW, 236 NBW) | -/- | Urban (n 38); rural (n 80)/public hospitals | FAO adopted MDD-W | Based on past 24-h recall | – | 118 | Time of ANC initiation, pregnancy-induced hypertension, Fe and folic acid supplementation | Number of mothers with inadequate DD was higher among LBW infants (adjusted OR = 3·75; 95 % CI 1·64, 8·57) | |
| Jamalzehi and colleagues, 2018(44) | Iran/cohort | 400 pregnant women | 29·69 (sd 2·94)/third trimester | –/health centres | Kant method (based on the number of groups and subgroups of foods) | FFQ (for last 3 months) and 2 d 24-h recall | 8/low DDS: < 3 | – | – | There was significant negative correlation between mothers DD and infants birth weight (β = −0·370, P = 0·008) | |
| Madlala, 2017(45) | South Africa/cohort | 172 black singleton pregnant women | 18–41/second and third trimester | Urban/antenatal care settings | FAO adopted DDS | Based on 24-h recall | 9/low DDS: ≤ 3; medium DDS: 4–5; high DDS: ≥ 6 food groups | 8/1 | 5 | There was significant negative correlation between mothers DD and infants birth weight (r −0·16; P = 0·04) | |
| Manerkar and colleagues, 2017(35) | India/cohort | 121 pregnant women | 25·16 (sd 3·61)/second and third trimester | Urban/antenatal clinics | FAO adopted DDS | Based on 24-h recall | 9/low DDS ≤ 3 food groups; high DDS ≥ 6 food groups | 19/0 | 15·7 | Chronic illness | Mothers DD did not differ between LBW and NBW infants |
| Nsereko and colleagues, 2020(48) | Rwanda/prospective cohort | 367 pregnant women | 28·12 (sd 6·01)/9–15 gestational weeks followed until delivery | Urban (n 120); rural (n 247)/health centres | FAO adopted MDD-W | FFQ previous day or night | 10/low DDS < 5 | 7/– | 2·1 | – | Maternal low MDD-W (OR: 3·36; 95 % CI 1·37, 8·26) was independent determinant of LBW |
| Quansah and Boateng, 2020(36) | Ghana/cross-sectional | 420 mothers attending postnatal clinic | 26·7 (sd 5·7)/post-natal | –/hospital | FAO adopted MDD-W using FFQ | – | 10/low DDS ≤ 5 | 184/88 | 43·8/60·7 | Age, education, employment, marital status, income, birth-order, parity, ANC attendance, smoking, alcohol intake and supplement intake | Maternal low DDS was associated with higher odds of infant LBW (OR: 4·29; 95 % CI 1·24, 6·48) |
| Rammohan and colleagues, 2019(37) | India/cross-sectional | 230 newly delivered women and their babies | –/During 24–48 h after delivery | Urban and rural/hospitals | DD index (based on the intake status of fifty-four food items) | Based on over the last 30 d of pregnancy | DD score range: −1·278– 4·063 Low DD score: < −0·622 | /– | 51 | Women’s pre-pregnancy weight, complications during pregnancy, parity, place of residence, religion, education, type of ration card, type of family, social network with any medical person and income tertile | Women with low DD had significantly higher proportion of LBW babies compared with those in the medium or high DD category (OR: 2·245; 95 % CI 1·107, 4·556; P = 0·025) |
| Rashid and colleagues, 2018(38) | Haiti/case-control | Sixty-six infants (thirty-two LBW and thirty-four NBW) and their mothers | LBW: 27·63 (sd 6·3) NBW: 27·6 (sd ± 5·5)/after delivery | Urban/hospital | FAO adopted women’s DDS | Based on past 24-h recall | 9/low DD: <5; high DD: ≥5 | 32/9 | 28 | – | Mean of DDS did not differ between mothers of LBW and NBW infants Number of mothers with DDS <5 was non-significantly higher in LBW infants’ group (28 %) compared with NBW infants’ group (18 %) |
| Saaka, 2013(39) | Ghana/cohort | 524 singleton pregnant women and their infants | 26·7(sd 5·2)/between 34 and 36 weeks of gestation | Urban/hospital | FAO modified DD questionnaire | FFQ based on past 24-h recall | 12/low DD: ≤ 7 food groups; high DD: ≥ 8 food groups | 89/ | 17·0 | Maternal age, GA, educational level, gender of baby, GWG, uptake of sulphadoxine pyrimethamine, frequency of ANC attendance and anaemia during pregnancy, preterm delivery and household wealth index | There was a significant difference in adjusted mean birth weight between women on low and high diversified diets, F(1, 415) = 8·935, P = 0·003 Maternal high DDS was associated with reduced risk of LBW infants (adjusted OR: 0·43; 95 % CI 0·22, 0·85; P = 0·014) Mothers with low DDS had 2·3 times increased risk of delivery LBW babies compared to those with high DDS (adjusted OR: 2·3; 95 % CI 1·18, 4·78; P = 0·014) |
| Tela and colleagues, 2019(40) | Ethiopia/cohort | 332 singleton pregnant mothers and their infants | Mean 28·5/before delivery | Urban (98·8 %)/private health facilities | Women’s DDS | Based on past 24- h recall | 9/low DDS: ≤3; medium DDS: 4–6; high DDS: 7–9 | – | – | Women with hearing and speaking difficulty, with pre-existing or current medical conditions and women with twin pregnancy were excluded | Mothers with high DDS had significantly larger babies than those with the low score (P < 0·0001)There was no association between maternal DD and infant birth weight (β: 0·066; 95 % CI −13, 54; P = 0·23) |
| Vanié and colleagues, 2019(46) | Côte d’Ivoire/retrospective | 146 newborns and mothers | 28·44 (sd 5·88)/third trimester | –/maternity hospitals | FAO adopted women’s DDS | 24-h recall | 9/low DDS: ≤3; medium DDS: 4–5; high DDS: ≥6 | 11 | 7·6 | Education, gestational weight gain, well-being index, alcohol consumption | The mean birth weight of newborns of mothers with medium and high DDS was higher (adjusted OR = 0·386; 95 % CI 0·072, 0·699; P = 0·017 and adjusted OR = 0·233; 95 % CI 0·016, 0·450; P = 0·036) |
| Zerfu and colleagues, 2016(41) | Ethiopia/cohort | 374 pregnant women (followed until delivery) and their infants | Low DDS: 25·54 (sd 0·347) Adequate DDS: 24·44 (sd 0·30)/second trimester | Rural/health centres | Women’s DDS | Four 24- h recall | 9/inadequate DDS: ≤3 Adequate DDS: ≥4 food groups | 34/ 23 | 9·1/ 67·65 | MUAC, level of education, Hb, age, height, GA | Women with inadequate DDS had higher risk of LBW infants (ARR: 2·06; 95 % CI 1·03, 4·11). Mean infants’ birth weight was significantly lower in mothers with low DDS (P < 0·001) |
ARR, adjusted relative risk; DDiv, dietary diversity; DDS, dietary diversity score; FFQ, food frequency questionnaire; LBW, low birth weight; NBW, normal birth weight; ANC, antenatal clinic (care); GA, gestational age; GWG, gestational weight gain; OR, odds ratio; FAO, Food and Agriculture Organisation; MDD-W, Minimum Dietary Diversity for Women.
Quality of articles
All included studies were rated as good quality (online supplementary material, Supplemental Tables 3 and 4). Quality scores for cohort studies ranged from six to eight (out of nine representing the lowest degree of bias) (online supplementary material, Supplemental Table 3). Main concern was comparability of exposed and unexposed participants based on design or analysis. The key potential confounding factors including age of mothers and infants’ gender were not taken into account in the analysis of seven studies (out of ten cohort studies). Quality scores for case-control studies ranged from six to seven (out of nine) (online supplementary material, Supplemental Table 4). Main concerns were comparability of cases and controls on the basis of the design or analysis and non-response rate of the groups. None of the five case-control studies controlled the role of gender in the analysis and indicated dropout rate.
Dietary diversity and low birth weight
Eighty percentage of the studies (twelve of fifteen) indicated that a low maternal DDS during pregnancy is associated with an increased risk of LBW in infants. In a study on 578 singleton pregnant women, Abubakari et al. (33) showed that mothers with LBW infants had significantly lower DDS. Ahmed et al. (34), studying 279 singleton live births, found that mothers with low DDS had about seven times higher odds of having LBW babies. A significant negative correlation between mothers’ dietary diversity and infant birth weight has also been reported by Madlala(45). In a study involving 420 mothers, Quansah(36) observed that among mothers with low DDS, the number of LBW infants was about two-fold that of normal birth weight (NBW) infants and the risk of LBW infants was four times higher in the low DDS group compared with the high DDS group. Rammohan et al. (37), investigating 230 newly delivered women, indicated that women with low dietary diversity had a significantly higher proportion of LBW babies compared with those in the medium or high dietary diversity category. Saaka(39), in a study on 524 singleton pregnant women, showed that the mean birth weight of infants was significantly lower among women with low DDS compared with women who consumed diversified diets. The author reported that a high maternal DDS was significantly associated with a reduced risk of LBW and women with low DDS were 2·3 times more likely to deliver LBW babies than those with high DDS. Tela et al. (40), in a study on singleton pregnant mothers, showed that mothers’ DDS was significantly associated with mean birth weight of infants and mothers with high DDS had significantly larger infants than those with low DDS. Zerfu et al. (41), studying 374 pregnant women, found that women with inadequate DDS had a significantly higher risk of LBW and the infants’ mean birth weight was significantly lower in the inadequate group. Bekela et al. (49) in a study on 354 mother–neonate indicated that number of mothers with inadequate dietary diversity was higher among LBW infants. Nsereko et al. (48), studying 367 pregnant women, showed that maternal low dietary diversity was independent determinant of LBW. Vanié et al. (46) and Jamalzehi et al. (44) also reported that the mean birth weight of newborns of mothers with low dietary diversity was significantly lower.
However, three of the included studies did not find any relationship between maternal DDS and newborn LBW. Manerkar et al. (35), studying 121 pregnant women (nineteen LBW, 102 NBW), reported no difference in maternal DDS between the LBW and NBW groups. Rashid et al. (38), in a study on sixty-six infants (thirty-two LBW and thirty-four NBW), showed that mean DDS did not differ between mothers giving birth to LBW and NBW infants. However, the number of mothers with low DDS was non-significantly higher in the LBW group (28 %) compared with the NBW group (18 %). Alemu and Gashu(47) also reported that maternal low dietary diversity is not associated with LBW.
Discussion
The current study identified fifteen observational studies that assessed the relationship of maternal dietary diversity during pregnancy and LBW risk in offspring. The results of the reviewed articles indicate that maternal gestational DDS is negatively associated with the risk of LBW in infants. However, Manerkar et al. (34), Rashid et al. (37) and Alemu and Gashu(47) did not observe such association. The small number of LBW infants and neglection of potential confounding factors on crosstalk between maternal dietary diversity and occurrence of LBW might have affected the finding.
Several maternal factors including age, smoking, chronic diseases, seasonality of food availability and socio-economic factors have been shown to be associated with maternal DDS. Gitagia et al. (50), in a cross-sectional study, reported age as an important determinant of dietary diversity among women of reproductive age. Alkerwi et al. (51) demonstrated an inverse association between the intensity of smoking and overall diet quality and reported that heavy smokers exhibited less dietary diversity in their food choices. The prospective cohort study of Conklin et al. (52) showed that higher diet diversity was correlated with a 30 % lower risk of developing type 2 diabetes in the United Kingdom. Besides, these maternal factors during pregnancy have been reported to act as risk factors for having LBW infants. The results of a systematic review showed that excessive gestational weight gain is associated with increased infant weight and that insufficient gestational weight gain is a risk factor for LBW infants(53). In a cohort study, Restrepo-Méndez(8) demonstrated that very young (< 16 years) or advanced maternal age (≥ 35 years) was associated with enhanced odds of LBW infants. Maternal smoking, heavy alcohol drinking and chronic diseases such as hypertension and diabetes have also been reported as risk factors for having LBW infants(12,13,15). Moreover, seasonality of food availability may act as a confounder in dietary diversity surveys in developing countries. It has been reported that food availability and access are strongly affected by seasonality and are associated with both maternal and child nutritional status(54,55).
Socio-economic status of the household is another factor that may influence dietary diversity of both mother and child. Mayén et al. (56) in a systematic review study found that high socio-economic status was associated with higher diet quality and diversity, in low- and middle-income countries. Kiboi et al. (57) in a cross-sectional study on 254 pregnant women showed socio-economic factors including education level, employment status, monthly income, household assets and land ownership as effective factors on dietary diversity of the women. Rammohan et al. (37), in a study on 230 newly delivered women, reported that low maternal education and economic status were significantly associated with poor dietary diversity of the women.
Evidence from several studies indicated that nutrition supplements (such as Fe and folic acid) intake may be inversely or positively correlated with LBW(58–60). Intake of nutrient supplements may promote maternal resistance to infections during pregnancy, ameliorate nutritional status and improve birth consequences(59). An overview of twenty-three systematic reviews of randomised controlled trials focusing on nutritional interventions before or during gestation showed that multiple micronutrients supplementation and improving maternal nutritional status positively influence LBW(60).
Taken together, the above-mentioned factors can be interpreted as having a confounding effect on the relationship between DDS and LBW. However, this concern has not been addressed in several studies reviewed.
Apparently, dietary diversity during pregnancy prevents neonate LBW by affecting maternal gestational weight gain. It has been reported that high maternal dietary diversity during pregnancy positively contributes to her gestational weight gain(61). Evidence indicates that mothers with higher gestational weight gain tend to deliver heavier babies(40,62). Besides, dietary diversity during pregnancy minimises the occurrence of nutritional deficiencies, in particular the development of anaemia in mothers which, in turn, leads to the improvement of fetal growth. The results of systematic reviews and meta-analysis studies demonstrated a significant association between maternal anaemia and infant LBW(63,64). Zerfu et al. (41) suggested that maternal dietary diversity during pregnancy is linked to a decreased risk of anaemia in the mother. In a cohort study involving 1675 pregnant women, Ghosh et al. (65) reported that dietary diversity is positively associated with serum Hb. However, other studies found no such association(66).
Various criteria or cut-off points were used to identify inadequate dietary diversity across the studies which may influence the accuracy of the results. None of the studies indicated accuracy of the criteria or cut-off points in predicting newborns’ LBW risk. Thus, it was needed to perform appropriate statistical methods such as receiver operating characteristic analysis to determine optimal threshold and to calculate the sensitivity and specificity of the different criteria or cut-off points in predicting risk of LBW.
Dietary diversity scoring was based on the number of food groups consumed by individuals, in the reviewed articles. Around 86·6 % of the reviewed articles used FAO adopted tools of WDDS (53·33 %) or MDD-W (33·33 %) for the assessment of dietary diversity. The differences between the two indicators are in the number of food groups, with nine groups in WDDS and ten in MDD-W(32). The food groups of WDDS include starchy foods, dark green leafy vegetables, meat and fish, other vegetables and fruits, vegetables and fruits rich in vitamin A,organ meats, milk and dairy products, eggs, legumes, nuts and seeds. The food groups of MDD-W are composed of grains, white roots and tubers, and plantains; pulses (beans, peas and lentils); nuts and seeds; dairy; meat, poultry and fish; eggs; dark green leafy vegetables; other vitamin A-rich fruits and vegetables; other vegetables and other fruits(32). In MDD-W, vegetables and fruits combined in one group but have separated in MDD-W. Therefore, according to the similarity of food groups between the two indicators, it seems that the method of dietary diversity scoring or the type of tool used for dietary diversity assessment are not factors that bias the findings.
Limitations of the review
Most studies conducted in urban areas, while rural areas have been neglected. In several studies, the dietary diversity data were collected after giving birth, a time that might not reflect the infant birth weight. Food intake information was collected retrospectively in most of the studies, a fact that may increase reporting bias(67). Using methods which employ health workers/proficient enumerators who are able to bring a cultural knowledge of local foods may help to avoid such biases(68). In addition, the period of data collection only comprised the previous 24 h, which might not be indicative of individual habitual intake. The number of LBW infants was too small in several studies, which makes the results controversial. Furthermore, there are many potential variables that can influence maternal DDS and the risk of LBW, including maternal age, gestational weight gain, gestational age, chronic diseases, smoking, alcohol use, gender of baby, infant congenital anomalies, nutritional supplements intake, seasonality of food availability and socio-economic factors and twin pregnancy. However, the confounding effects of these variables have not been addressed in several studies or the number of factors taken into account was too small.
This review is restricted by lack of study from developed countries. The scoring of low dietary diversity varied across the studies which make it difficult to compare results across studies. Lack of interventional study was another limitation. Further evidence from interventional studies is needed to confirm findings from observational studies.
Implication of the findings
The findings of the current study imply an interaction between DDS and LBW. Thus, it is suggested that implementation of nutrition education and counselling in pregnancy(69,70) and peri-conceptional(70) care processes are helpful to improve birth outcomes. In addition, improving maternal nutritional status through multiple micronutrients supplementation during pregnancy might be an effective strategy to reduce the risk of LBW in newborns(60,71,72,73). Such interventions must be incorporated in health promotion strategies targeting the peri-conceptional and pregnant mothers in order to improve their dietary diversity. However, there is a need to further identify environmental factors contributing to poor DDS, in particular among low- and middle-income communities. Furthermore, pregnant mothers with poor dietary diversity must be regularly screened and properly identified and the importance of a healthy and diverse diet during pregnancy must be emphasised.
Conclusion
The results of the present study suggest that high maternal dietary diversity during pregnancy may be associated with the risk of LBW infants in developing countries.
Acknowledgements
Acknowledgements: None. Financial support: The current study was supported by Tabriz University of Medical Sciences. Conflict of interest: There are no conflicts of interest. Authorship: Both of the authors were involved in the searching and selection of the articles, data extraction and participated in manuscript writing. Both of the authors read and approved the final manuscript. Ethics of human subject participation: The protocol of the study was registered and approved in the Research Vice Chancellor of Tabriz University of Medical Sciences (IR.TBZMED.REC.1399.150) (http://ethics.research.ac.ir/IR.TBZMED.REC.1399.150) grant number of the article as follows: Grant No: 64878.
Supplementary material
For supplementary material accompanying this paper visit https://doi.org/10.1017/S1368980021000276.