When a negative shock aﬀects a cohort in utero, two things may happen: ﬁrst, the population suﬀers detrimental consequences in later life; and second, some will die as a consequence of the shock, either in utero or early in life. The latter eﬀect, often referred to as culling, may induce a bias in estimates of later life outcomes. When the health shock disproportionately aﬀects a positively selected subpopulation, the long-term eﬀects are overestimated. The 1918 ﬂu pandemic was plausibly more harmful to mothers of high socioeconomic status, as a suppressed immune system in mothers of low socioeconomic status may have been protective against the most severe consequences of infection. Using historical birth records from the city of Bern, Switzerland, we assess this concern empirically and document that a careful consideration of culling is paramount for the evaluation of the 1918 ﬂu pandemic and other fetal health shocks.