According to the Centers for Disease Control and Prevention (CDC), pregnancy-related mortality (deaths) in the United States has been increasing over the past 30 years, with significant variation by race or ethnicity and age of the pregnant woman. These increasing deaths result from increased risk of developing metabolic diseases (such as diabetes), cardiovascular disease (CVD) risk factors, and actual cardiovascular disease. Previous research has demonstrated a high prevalence of poor diet quality among US women before, during and after pregnancy. In addition, a Mediterranean diet pattern has been linked to health and longevity. These notions led to a recent study in the journal JAMA Network Open that evaluated the association between eating a diet including foods characteristic of the Mediterranean pattern adapted for the US population, and the chance of developing any adverse pregnancy outcome.
The study evaluated the association between an Alternate Mediterranean Diet score and odds of developing any adverse pregnancy outcome or individual adverse pregnancy outcomes using existing data on a population of pregnant women. The study was conducted at 8 US medical centers between 2010-2013, with 10,038 first time mothers with existing pregnancies (only one fetus) in their first trimester. The mothers were followed through delivery of their babies. Some mothers were excluded from the current study based on factors such as incomplete diet data, implausible energy intakes, and history of chronic hypertension or diabetes, resulting in a final sample size of 7798 for analyses.
This study assessed diet around the time of conception using a standard questionnaire (Block 2005 Food Frequency Questionnaire) at the first study visit between 6 and 13 weeks. The questionnaire evaluated regular eating habits during the past 3 months by asking participants about the amount and frequency of consumption of 120 food and beverage items to assess intakes of 52 nutrients and 35 food groups. The questionnaire was administered in English or Spanish.
The questionnaires were scored in a standard way The scores consisted of nine components: vegetables (excluding potatoes), fruits, nuts, whole grains, legumes, fish, monounsaturated to saturated fat ratio, red and processed meats and alcohol. For each component, those with intake above the most common level received a score of 1; those with intakes below the most common level for red and processed meat consumption were assigned a score of 1; for alcohol intake, women who consumed between 5 and 15 g/d received a score of 1. All scores were summed to create an overall diet score ranging from 0 to 9 – with higher scores representing closer resemblance to the Mediterranean diet.
The primary outcome of this study was the development of any adverse pregnancy outcomes, defined as developing 1 or more conditions from the following list: gestational hypertension, preeclampsia or eclampsia, gestational diabetes, preterm birth (medically indicated or spontaneous live birth at <37 weeks’ gestational age – assessed as both a composite and as spontaneous or iatrogenic preterm birth), delivery of a small-for-gestational-age infant (<5th percentile by Alexander nomogram), or stillbirth.
This study included 7798 participants with a mean age of 27.4 years and 9.7% aged 35 or older. The racial/ethnic distribution was 4.3% Asian, 16.6% Hispanic, 10.5% non-Hispanic Black, and 63.9% non-Hispanic White. About half were educated with a college degree or above, 64.5% were married and 19.5% had obesity. The average Mediterranean diet score was 4.3 (2.1). Comparing across categories of the score, those with higher scores were more likely to be older, Non-Hispanic White, married and never smokers, have higher education levels and less likely to have a body mass index in the obesity category than those with lower scores. The differences were viewed as significant based on statistical analysis. Those in the high vs low category had significantly lower overall occurrence of any adverse pregnancy outcomes, including one of the more common adverse outcomes, preeclampsia. The study also found that for women with advanced maternal age, the diet was connected to a protective effect by reducing their pregnancy complications. No connection was found between pregnancy complications and the diet for certain racial/ethnic groups or based on the body mass index of mothers before pregnancy.
Strengths of the Study
This study has notable strengths, such as its geographic and racial/ethnic diversity representative of the US population; rigorous assessment of maternal characteristics and pregnancy complications; forward looking (prospective) design with diet data collected prior to occurrence of adverse pregnancy outcomes; a reliable questionnaire to measure habitual diet and the use of a standard scoring system representing a recommended healthy dietary pattern adapted for US populations. These findings could help inform dietary strategies to improve health during pregnancy.
This study is the largest population-based US forward prospective cohort study examining a Mediterranean diet pattern around the time of conception and its association with adverse pregnancy outcomes and is the first to evaluate potential differences by maternal age, BMI, race and ethnicity. Results suggest that a Mediterranean diet pattern is associated with lower risk for any adverse pregnancy outcomes and multiple individual adverse pregnancy outcomes in US women, with a dose-response association. Dose-response means that more of the diet seems to offer greater benefits. This adds to existing evidence showing the Mediterranean diet may be important for preserving the health of women across the lifespan, including during pregnancy. Long-term intervention studies are needed to assess whether promoting a Mediterranean-style diet pattern around the time of conception can prevent adverse pregnancy outcomes or reduce heart disease risk, particularly among those at high risk.