[grey_whiskers]

Yes, I understand. But if you you’re looking for detrimental effects of the jab, then you compare (women jabbed in 1st trimester) to (women not jabbed in first trimester) for example.

[palmer]

then you compare (women jabbed in 1st trimester) to (women not jabbed in first trimester)

They get two jabs in this study so jabbed in first will very likely get jabbed in second or third. There will be very few cases in the "first but not second or third" group.