Background Nausea and/or vomiting in pregnancy (NVP) is reported in the majority of pregnancies. Experiences of NVP vary greatly, but little is known about the consequences of NVP on pregnancy diet.

Methods The Southampton Women’s Survey has measured the diet, body composition, physical activity and social circumstances of 12,583 non-pregnant women aged 20 to 34 years living in the city of Southampton, UK. Women who subsequently became pregnant were studied in early pregnancy (median gestation = 11.9 weeks). Before and in early pregnancy dietary intake over the preceding 3 months was assessed using a food frequency questionnaire. Experience of NVP in early pregnancy was graded as none, mild (nausea only), moderate (sometimes sick) or severe (regularly sick, can’t retain meals). Principal component analysis of the dietary data collected before pregnancy identified a ‘prudent’ (healthy) dietary pattern. Prudent diet scores were calculated for each woman in both early and late pregnancy describing their compliance with this pattern; paired scores were available for 2270 women.

Results In early pregnancy 89% of women were nauseous, although most commonly the NVP experienced was mild (48%) or moderate (30%); 11% of women had severe NVP symptoms. Women experiencing more nausea were more likely to be from a lower social class, to be more obese, to be younger and to be multiparous. Increasing severity of NVP was non-significantly associated with a fall in energy intake (P = 0.09); after adjustment for confounders women with no nausea had an average energy intake that was 91 kcal/day higher in early pregnancy than before pregnancy, whereas for women with severe nausea, average energy intakes were 14 kcal/day less than before pregnancy. Increasing severity of NVP was associated with a fall in prudent diet score (P < 0.001); after adjustment for confounders women with no nausea had a prudent diet score on average 0.12 SD higher in pregnancy than before pregnancy, whereas those with severe nausea had a prudent diet score on average 0.19 SD lower in early pregnancy than before pregnancy.

Conclusion Gestational diet is increasingly recognised as having important consequences for offspring health. The impact of nausea on energy intake is small. Of much greater concern is the potential detrimental effect of nausea on dietary quality as reflected by the prudent diet score. Pregnancy is a time when women face an increase in micronutrient needs and women with more severe nausea may be particularly at risk of poorer quality diets.