Design: multisite, randomised, controlled trial
Population: 2,137 pregnant women whose unborn child had at least two biological relatives with diagnosed allergic disease
Primary outcome: IgE-mediated egg or peanut allergy in the infant at 1 year
Effect: 7.8% vs 8.4%, relative risk 0.93 (95% CI 0.69 to 1.26), P = 0.65

PrEggNut randomised 2,137 pregnant women whose unborn child had at least two biological family members with medically diagnosed allergic disease. From before 23 weeks until 4 months postnatally, one group ate at least 6 eggs and 60 peanuts a week; the other kept to no more than 3 eggs and 30 peanuts. The primary outcome was IgE-mediated egg or peanut allergy in the infant at 1 year.

Allergy occurred in 83 of 1,066 infants (7.8%) in the high-intake group and 89 of 1,064 (8.4%) in the standard group, relative risk 0.93 (95% CI 0.69 to 1.26). Safety measures were similar. This is a clean answer to a question that has circulated for two decades: in utero and breast-milk allergen exposure, deliberately increased, does not lower allergy risk in the infants at highest familial risk.

What this does not do is reopen maternal avoidance. Both groups ate eggs and peanuts; the trial compared more with some, not some with none. The counselling that follows is unchanged and worth stating plainly to anxious families: eat normally in pregnancy, and introduce egg and peanut to the infant in a timely way after weaning starts, which is where the randomised evidence for prevention actually sits.

Reassure families with an allergic history that no special maternal diet is needed
Do not advise maternal avoidance either - it has no benefit and risks nutritional shortfall
Keep the prevention conversation on the infant: early, sustained introduction after weaning begins
Record the family allergy history so the paediatric team can plan introduction
Where peanut is not a routine weaning food locally, discuss a practical form the family will use

Why it matters

The idea that maternal diet in pregnancy can be tuned to prevent food allergy has been guiding advice without randomised support - and now has it, negative.

The statistics, in plain English

A relative risk of 0.93 with a confidence interval running from 0.69 to 1.26 includes 1.0, so the data are compatible with a modest benefit, no effect, or a modest harm. With more than 1,000 women per arm and an 8% event rate, the trial had a reasonable chance of finding a large effect; it did not. The honest reading is not 'probably helps a little' but 'no useful effect demonstrated'.