OBJECTIVE: To investigate the possible association between birth outcome and marine food and cod liver oil intake of healthy women in early (prior to 15 weeks of gestation) pregnancy.

DESIGN: An observational study.

SETTING: Free-living conditions in a community with traditional fish and cod liver oil consumption.

POPULATION: Four hundred and thirty-five healthy pregnant Icelandic women without antenatal and intrapartum complications.

METHODS: Dietary intake of the women was estimated with a semi-quantitative food frequency questionnaire (FFQ) covering food intake together with lifestyle factors for the previous three months. Questionnaires were filled out at between 11 and 15 weeks and between 34 and 37 weeks of gestation. The estimated intake of marine food and cod liver oil was compared with birthweight by linear and logistic regression controlling for potential confounding.

MAIN OUTCOME MEASURES: Birthweight, cod liver oil intake, lifestyle factors (alcohol, smoking).

RESULTS: Fourteen percent of the study population used liquid cod liver oil in early pregnancy. Regression analysis shows that these women gave birth to heavier babies (P < 0.001), even after adjusting for the length of gestation and other confounding.

CONCLUSIONS: Maternal intake of liquid cod liver oil early in pregnancy was associated with a higher birthweight. Higher birthweight has been associated with a lower risk of diseases later in life and maternal cod liver oil intake might be one of the means for achieving higher birthweight.