Does a Mediterranean-type diet consumed in pregnancy reduce the risk of premature delivery?
Preterm delivery is delivery earlier than three weeks before expected date of delivery and occurs in 5-10% of pregnancies in European countries. Preterm delivery accounts for the majority of neonatal deaths and is also associated with increased rates of infections and other diseases in the infancy. In addition, preterm born infants have increased rates of significant permanent mental, neurological, or physical malfunctions or handicaps. It is therefore an important task to identify modifiable causes of preterm delivery
Until today few factors with a causal relation to preterm birth have been identified. Many studies have focused on the woman’s diet, but most of these studies have been discouraging. Some studies indicated that marine omega-3 fatty acids could prolong duration of pregnancy and reduce recurrence risk of preterm birth, whereas others have been unable to support these findings. A high intake of antioxidants has also been associated with lower risk, but studies have provided contradictory evidence.
Mediterranean diet in pregnancy-results of a dietary intervention study
Recently, Khoury and collaborators provided important input into this field. They randomly allocated 290 healthy pregnant Norwegian women to an intervention group who were advised to change their diet towards a Mediterranean-type diet, and a control group who did not receive advice to change diet. The aim of the study was to investigate the impact of a cholesterol-lowering diet on maternal and cord cholesterol levels and on health of the offspring. The authors showed convincing data from repeated dietary assessments that, compared to controls, the women in the intervention group did change their diet towards the aimed pattern. The women in the intervention group also had lower low-density lipoprotein in maternal blood, as expected. Unexpectedly, however, and interestingly in this context, they found substantially fewer preterm births in the intervention group compared to the control group: only 1 preterm birth occurred in the intervention group, whereas 11 occurred in the control group. This corresponded to a prevalence of 0.7 and 7.4%, respectively, and a relative risk of 0.10.
A prospective cohort study showed similar results
We set out to replicate this unexpected finding in a large observational cohort established in Denmark. During 1996-2002 we assessed dietary intake among 70,000 women by means of a food frequency questionnaire completed in mid-pregnancy. Exposure groups were defined to match as closely as possible the comparison groups in the randomised controlled trial of Khoury and collaborators.
Women consuming a Mediterranean-type diet were those who ate fish twice a week or more, used olive or rape seed oil, consumed 5 fruits and vegetables a day, ate meat (other than poultry and fish) at most twice a week, and drank at most 2 cups of coffee a day. Only non-smokers were included. Of 35,530 women, 1,137 (3.2%) fulfilled all Mediterranean-type diet criteria, and 540 (1.5%) none. Odds ratios for preterm birth and early preterm birth were 0.61 (95% Confidence Interval (CI): 0.35 to 1.05) and 0.28 (0.11 to 0.76), respectively, in Mediterranean-type diet women compared to women fulfilling none of the Mediterranean-type diet criteria. Strengths of our study include its size and prospective design. The main limitation of our study was its observational design, and the possibility that a Mediterraneantype diet may be a marker for a generally healthier lifestyle cannot be ruled out, although we adjusted (by statistical multivariate techniques) the results for factors such as the woman’s education and age.
We concluded that shifting towards a Mediterranean-type diet during pregnancy may reduce the risk of early delivery in Danish women. The issue has also been explored in a parallel study based on data from another large observational cohort established in Norway, the Norwegian Mother Child-Cohort. However, in that study it was not possible to detect any association between intake of a Mediterranean-type diet and risk of preterm birth. Clearly there is need for more research. The findings should be replicated in other birth cohorts and trials. One difficulty is that Mediterranean diets may not be a very well-defined entity and may be defined in several different ways according to the emphasis.
- Khoury J, Henriksen T, Christophersen B, Tonstad S. Effect of a cholesterol-lowering diet on maternal, cord, and neonatal lipids, and pregnancy outcome: a randomized clinical trial. American Journal of Obstetrics and Gynecology 2005; 193: 1292-301.
- Mikkelsen TB, Østerdal ML, Knudsen VK, Haugen M, Meltzer HM, Bakketeig L, Olsen SF. Association between a Mediterranean-type diet and risk of preterm birth among Danish women: a prospective cohort study.
- Acta Obstetricia et Gynecologica Scandinavica 2008; 87: 325-30.
- Haugen M, Meltzer HM, Brantsaeter AL, Mikkelsen T, Østerdal ML, Alexander J, Olsen SF, Bakketeig L. Mediterranean-type diet and risk of preterm birth among women in the Norwegian Mother and Child Cohort Study (MoBa): a prospective cohort study. Acta Obstetricia et Gynecologica Scandinavica 2008; 87: 319-24.