Format

Send to

Choose Destination
Proc Natl Acad Sci U S A. 2015 Apr 21;112(16):E2102-11. doi: 10.1073/pnas.1416546112. Epub 2015 Mar 30.

The human sex ratio from conception to birth.

Author information

1
Fresh Pond Research Institute, Cambridge, MA 02140; orzack@freshpond.org.
2
Fresh Pond Research Institute, Cambridge, MA 02140;
3
Genzyme Genetics, Westborough, MA 01581;
4
Reprogenetics, Livingston, NJ 07039;
5
Oxford University, Oxford OX1 3TG, United Kingdom; and.
6
Harvard Medical School and Brigham and Women's Hospital, Boston, MA 02115.

Abstract

We describe the trajectory of the human sex ratio from conception to birth by analyzing data from (i) 3- to 6-d-old embryos, (ii) induced abortions, (iii) chorionic villus sampling, (iv) amniocentesis, and (v) fetal deaths and live births. Our dataset is the most comprehensive and largest ever assembled to estimate the sex ratio at conception and the sex ratio trajectory and is the first, to our knowledge, to include all of these types of data. Our estimate of the sex ratio at conception is 0.5 (proportion male), which contradicts the common claim that the sex ratio at conception is male-biased. The sex ratio among abnormal embryos is male-biased, and the sex ratio among normal embryos is female-biased. These biases are associated with the abnormal/normal state of the sex chromosomes and of chromosomes 15 and 17. The sex ratio may decrease in the first week or so after conception (due to excess male mortality); it then increases for at least 10-15 wk (due to excess female mortality), levels off after ∼20 wk, and declines slowly from 28 to 35 wk (due to excess male mortality). Total female mortality during pregnancy exceeds total male mortality. The unbiased sex ratio at conception, the increase in the sex ratio during the first trimester, and total mortality during pregnancy being greater for females are fundamental insights into early human development.

KEYWORDS:

demography; development; evolution; genetics; sex ratio

Comment in

PMID:
25825766
PMCID:
PMC4413259
DOI:
10.1073/pnas.1416546112
[Indexed for MEDLINE]
Free PMC Article

Supplemental Content

Full text links

Icon for HighWire Icon for PubMed Central
Loading ...
Support Center