Nutrition is a predictor of pregnancy success and dietary patterns can affect pregnant women for the rest of their lives. The overall diet quality of pregnant women in Shanghai was found in this study to be average, and unbalanced, which is similar to the previous findings of Shanghai residents . The median CHDI score was 71.5 and merely 18.4% scored ≥ 80 points, which is higher than that of a national sample 7 and Shanghai senior high school students . Pregnancy stages and residential areas were associated with CHDI scores, as were socioeconomic factors (educational level and family income). The dietary scores of urban residents were higher than those of suburban and rural residents, and being in the later stages of pregnancy served as a protective factor for good dietary intake.
Pregnant women in Shanghai ate a wide variety of foods with an over-intake of meat and under-intake of whole grains, dairy products and vegetables. The under-consumption of whole grains, dry beans and tubers may be related to the diet habits of Shanghai residents, which is difficult to change in a short time. Whole grains and its constituents have antioxidants and anti-inflammatory properties, which promote fertility ; a fertility clinic study showed that a higher intake of whole grains was associated with better birth outcomes . Although the promotion of whole grain consumption has been on-going since the establishment of the Chinese Dietary Guidelines in 2016 , people in the southern region of China are accustomed to living on rice on a long-term basis, which leads to the insufficient consumption of whole grains, such as corn, millet, buckwheat and miscellaneous beans. The median dairy intake of the participants in this study was merely 200 g/d, which was far from the recommended intake for pregnant women (300–500 g/d). Milk products are excellent sources of calcium and protein for maternal and fetal health rather than other foods, and a chronic calcium deficiency may cause increased bone loss during pregnancy [18, 19]. Lactose intolerance is common in China as lactase deficiency affects 80%-90% of women three to four years after weaning, and 66.5% of adults have symptoms of lactose intolerance . Fermented dairy products, such as cheese and yogurt, are alternatives that are more suitable for individuals with lactose intolerance. Another diet problem lies in the severely inadequate consumption of total vegetables, dark green and orange vegetables and over-consumption of meat, which was also reported in a previous national survey in 2010–2012 . The median total intake of vegetables and livestock and poultry meat of the participants in this study was 158.6 g/d and 85.3 g/d, respectively. Interestingly, pregnant women were advised to have 300–500 g/d of total vegetables and 40–75 g/d of livestock and poultry meat and dark green and orange vegetables, which would account for over 66.7% of all the vegetables consumed . Several studies have proposed that a healthy diet comprised of sufficient vegetables is associated with a reduction in the risk of gestational diabetes mellitus during pregnancy while a higher consumption of total meat, especially red and processed meat, could increase the hazard [22, 23].
We found that participants in later pregnancy had a relatively higher overall diet quality compared to those in early pregnancy, which may be related to the stress of pregnancy. A cohort study from the FUDAN School of Public Health, which included 2634 participants, found that increased pregnancy-specific stress in the middle and third trimesters may motivate pregnant women to follow a healthy balanced diet, and thus, equip them with more nutritional knowledge compared to novices in their first trimester, which was thought as the weak association with poor birth outcomes in previous studies [24, 25]. Compared to the chronic stress experienced during early pregnancy, the stress in the later trimesters is acute stress, characterized by increased blood sugar and poor appetite, which lure pregnant women to choose food that stimulates their appetite to meet their nutritional needs prior to labor [26, 27]. Hence, it is important to strengthen diet-related health education for pregnant women during all trimesters, especially the first one.
Residential area was found to be another determining factor of dietary quality. The dietary scores of the urban residents were higher than those of the suburban and rural residents. People dwelling in the countryside tend to consume more refined grain and less vegetables and meat, which is consistent with the finding Dibsdall LA  and associated with the local food environment and food availability. Full-service supermarkets and grocery stores in downtown are more densely distributed than those in the remote areas are. Another explanation may be related to differences in socioeconomic status among the urban, suburban and rural areas. A large amount of epidemiologic data has revealed an association of diet quality with the socioeconomic status . Educational and family income levels were also found to be protective factors in our study, the distribution of which differed between the residential areas. Pregnant women with high educational levels have more opportunities to earn more money and settle downtown rather than in rural areas. They are likely to have higher rates of literacy and healthier dietary habits . Their work experience might empower them to make better decisions about their dietary healthcare during pregnancy , and thus, have a higher diet quality. Pregnant women with lower incomes tend to consume fewer fruits and vegetables and more sugar-sweetened beverages , as the cost of food is an insurmountable gap for them, making it a challenge to access nutrient-dense diets .
To the best of our knowledge, this is the first study to apply CHDI indicators to assess diet quality among pregnant woman in coastal areas across trimesters and residential areas. This investigation was a systematic sampling survey covering all districts of Shanghai using a large representative sample and reasonable survey methods, which reflects the dietary intake of the population and should lead to generalizable conclusions. However, our study has limitations. The CHDI has some drawbacks. Each CHDI score has only a single threshold and it cannot explain the balance of the overall dietary pattern of a target population. Too much or too little consumption of one food type is not fully reflected in the total score; furthermore, this imbalance also affects the scores on the other items. Thus, the CHDI score needs to be evaluated and combined with a quantitative assessment of dietary intake. Health outcomes were not assessed in this study, and thus, the relationship between the CHDI and health outcomes should be evaluated in the future.