TY - JOUR

T1 - Greater Loss of Female Embryos During Human Pregnancy: A Novel Mechanism

AU - Mulley, John F.

PY - 2019/11

Y1 - 2019/11

N2 - Given an equal sex ratio at conception, the excess of human males at birth can only be explained by greater loss of females during pregnancy. It is proposed that the bias against females during human development is the result of a greater degree of genetic and metabolic “differentness” between female embryos and maternal tissues than for similarly aged males, and that successful implantation and placentation represents a threshold dichotomy, where the acceptance threshold shifts depending on maternal condition, especially stress. Right and left ovaries are not equal, and neither are the eggs and follicular fluid that they produce, and it is further hypothesized that during times of stress, the implantation threshold is shifted sufficiently to favor survival of females, most likely those originating from the right ovary, and that this, rather than simply a greater loss of males, explains at least some of the variability in the human sex ratio at birth.

AB - Given an equal sex ratio at conception, the excess of human males at birth can only be explained by greater loss of females during pregnancy. It is proposed that the bias against females during human development is the result of a greater degree of genetic and metabolic “differentness” between female embryos and maternal tissues than for similarly aged males, and that successful implantation and placentation represents a threshold dichotomy, where the acceptance threshold shifts depending on maternal condition, especially stress. Right and left ovaries are not equal, and neither are the eggs and follicular fluid that they produce, and it is further hypothesized that during times of stress, the implantation threshold is shifted sufficiently to favor survival of females, most likely those originating from the right ovary, and that this, rather than simply a greater loss of males, explains at least some of the variability in the human sex ratio at birth.

KW - abortion

KW - endometrium

KW - implantation

KW - miscarriage

KW - ovarian asymmetry

KW - placentation

KW - pregnancy

U2 - 10.1002/bies.201900063

DO - 10.1002/bies.201900063

M3 - Article

VL - 41

JO - BioEssays : news and reviews in molecular, cellular and developmental biology

JF - BioEssays : news and reviews in molecular, cellular and developmental biology

SN - 0265-9247

IS - 11

ER -