Birth spacing observation In one study a trend towards a lower prevalence of doctor diagnosed hay fever was observed with closer birth spacing, but this was of only borderline significance (0 05 < p < 0 1) after adjustment for other factors ( 22 ).
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The sentences
But the independent inverse association between AR or atopy and number of younger siblings is highly significant because it precludes the birth order effect being attributable exclusively to any kind of adaption of the maternal-foetal interface with a mother's successive pregnancies.