Effects of Mediterranean Diet or Mindfulness-Based Stress Reduction on Prevention of Small-for-Gestational Age Birth Weights in Newborns Born to At-Risk Pregnant Individuals

Importance: Being born small for gestational age (SGA) is a leading cause of perinatal morbidity and mortality with no effective prevention or therapy. Maternal suboptimal nutrition and high stress levels have been associated with poor fetal growth and adverse pregnancy outcomes. Objective: To investigate whether structured interventions based on a Mediterranean diet or mindfulness-based stress reduction (stress reduction) in high-risk pregnancies can reduce the percentage of newborns who were born SGA and other adverse pregnancy outcomes. Design, Setting, and Participants: Parallel-group randomized clinical trial conducted at a university hospital in Barcelona, Spain, including 1221 individuals with singleton pregnancies (19-23 weeks' gestation) at high risk for SGA. Enrollment took place from February 1, 2017, to October 10, 2019, with follow-up until delivery (final follow-up on March 1, 2020). Interventions: Participants in the Mediterranean diet group (n = 407) received 2 hours monthly of individual and group educational sessions and free provision of extra-virgin olive oil and walnuts. Individuals in the stress reduction group (n = 407) underwent an 8-week stress reduction program adapted for pregnancy, consisting of weekly 2.5-hour sessions and 1 full-day session. Individuals in the usual care group (n = 407) received pregnancy care per institutional protocols. Main Outcomes and Measures: The primary end point was the percentage of newborns who were SGA at delivery, defined as birth weight below the 10th percentile. The secondary end point was a composite adverse perinatal outcome (at least 1 of the following: preterm birth, preeclampsia, perinatal mortality, severe SGA, neonatal acidosis, low Apgar score, or presence of any major neonatal morbidity). Results: Among the 1221 randomized individuals (median [IQR] age, 37 [34-40] years), 1184 (97%) completed the trial (392 individuals assigned to the Mediterranean diet group, 391 to the stress reduction group, and 401 to the usual care group). SGA occurred in 88 newborns (21.9%) in the control group, 55 (14.0%) in the Mediterranean diet group (odds ratio [OR], 0.58 [95% CI, 0.40-0.84]; risk difference [RD], -7.9 [95% CI, -13.6 to -2.6]; P = .004), and 61 (15.6%) in the stress reduction group (OR, 0.66 [95% CI, 0.46-0.94]; RD, -6.3 [95% CI, -11.8 to -0.9]; P = .02). The composite adverse perinatal outcome occurred in 105 newborns (26.2%) in the control group, 73 (18.6%) in the Mediterranean diet group (OR, 0.64 [95% CI, 0.46-0.90]; RD, -7.6 [95% CI, -13.4 to -1.8]; P = .01), and 76 (19.5%) in the stress reduction group (OR, 0.68 [95% CI, 0.49-0.95]; RD, -6.8 [95% CI, -12.6 to -0.3]; P = .02). Conclusions and Relevance: In this randomized trial conducted at a single institution in Spain, treating pregnant individuals at high risk for SGA with a structured Mediterranean diet or with mindfulness-based stress reduction, compared with usual care, significantly reduced the percentage of newborns with birth weight below the 10th percentile. Due to important study limitations, these findings should be considered preliminary and require replication, as well as assessment in additional patient populations, before concluding that these treatments should be recommended to patients. Trial Registration: ClinicalTrials.gov Identifier: NCT03166332.