Do mothers selectively relax the screen for frail pregnancies?

What is it about?

Pregnancy serves as an opportunity not only for maturation but also for selection given that fewer than 50% of conceptions actually end in a live birth. Previous research asserts that older mothers, nearing the end of their reproductive lifespan, may be less selective about which of their conceptions ultimately survive to birth. We find some support that hCG, a maternal hormone, signals reduced selectivity against frail conceptions as the mother nears the end of her reproductive lifespan.

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Why is it important?

Our findings partially support that involuntary processes during pregnancy, especially for mothers nearing the end of reproductive age, act to relax the maternal screen in utero for relatively frail gestations. The hormone hCG appears to act as one component of maternal selectivity in determining which conceptions survive to birth. Our results, consistent with an evolutionary view, help explain why birth defects appear more common especially at lower birth order and at advanced maternal age.