Figure 1.

Schematic of the relaxed filter for spontaneous abortion. Right vertical line indicates a biomarker threshold by which a gravid mother screens for gestation quality. Only gestations to the right of the threshold survive to term. A ‘low expected marginal gain in fitness’ condition could include a birth to a mother of high parity. According to relaxed filter stringency, this threshold may relax, or ‘left-shift’, to the left vertical line if the expected marginal gain for carrying the gestation to term is relatively high (e.g. mother has no previous children). This relaxed filter condition would result in a relatively lower mean level of the biomarker among live births but a higher incidence of abnormal gestations carried to term. Adapted from Forbes [4].