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Parental aging synergistically decreases offspring sex ratio

Koji Matsuo1, Norichika Ushioda, Laurence C Udoff

  • 1Obstetrics, Gynecology, and Reproductive Sciences, University of Maryland School of Medicine, Baltimore, MD 21201, USA. koji.matsuo@gmail.com

The Journal of Obstetrics and Gynaecology Research
|February 14, 2009
PubMed

Insights

Advanced parental age, particularly paternal age, significantly decreases the male to female birth ratio. This study highlights the impact of parental age on offspring sex ratio (OSR).

Area of Science:

  • Reproductive Science
  • Human Demographics
  • Perinatal Epidemiology

Background:

  • The male to female birth ratio, known as the offspring sex ratio (OSR), is a key demographic indicator.
  • Observed declines in OSR warrant investigation into contributing factors, including parental characteristics.
  • Parental age is a potential, yet under-explored, factor influencing sex determination at conception.

Purpose of the Study:

  • To investigate the effect of parental age on the offspring sex ratio (OSR).
  • To determine if increasing paternal or maternal age influences the male to female birth ratio.
  • To examine potential synergistic effects of advanced parental ages on OSR.

Main Methods:

  • Prospective multicenter study involving 3,049 deliveries across five Japanese hospitals (August 2005 - February 2007).
  • Exclusion of multiple pregnancies and assisted conceptions; recording of periconceptional parental ages.
  • Statistical analysis using chi-squared or Fisher's exact tests to compare OSR across parental age groups.

Main Results:

  • Paternal age of 40 or older was associated with a significantly smaller OSR (0.75 vs. 1.17, P = 0.001).
  • Advanced maternal age also correlated with a reduced OSR: 35-39 years (0.87) and 40+ years (0.63).
  • Synergistic effects were observed; OSR for parents both aged 40+ was significantly lower (0.52) than for parents aged 30-34 (1.17).

Conclusions:

  • Increasing paternal age demonstrably and synergistically decreases the male to female birth ratio.
  • Advanced maternal age also contributes to a lower offspring sex ratio.
  • Parental age is a significant demographic factor influencing human sex ratios at birth.
Abstract

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