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Harvard study reveals link between mother's age and child's sex

New research indicates older mothers may be more likely to have multiple children of the same sex.

August 2, 2025 at 11:00 AM

Harvard researchers find link between mother's age, child's sex

A recent study from Harvard explores how maternal age affects the sex of children born.

Harvard study reveals link between mother's age and child's sex

Research from Harvard T.H. Chan School of Public Health suggests a connection between a mother's age and the sex of her children. Published in the journal Science Advances, the study analyzed data from over 58,000 women. It found that women who have their first child at 29 or older are more likely to have subsequent children of the same sex compared to younger mothers. Furthermore, families with three children of the same sex are more inclined to have a fourth child of the same sex. This research sheds light on a previously debated topic, challenging the notion that the determination of a child's sex is purely random.

Key Takeaways

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The study involved over 58,000 women and their children.

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Mothers aged 29 or older are more likely to have children of the same sex.

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Families with three children of the same gender often have a fourth of the same sex.

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Previous theories on sex determination lacked large-scale validation.

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Significant factors included race, hair color, and height, but only age was impactful.

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The researchers emphasized that the findings are group trends, not predictions.

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The study invites further investigation into maternal health's effect on sex ratios.

"It's not necessarily random probability."

Dr. Bernard Rosner explains the significance of their findings.

"Instead, we hope it opens the door for investigation into maternal influences on offspring sex."

Siwen Wang discusses the study's broader implications.

The findings of this study may provide a fascinating insight into the interactions between maternal age and genetic factors influencing the sex ratio of children. While the results support the idea that older age could skew sex ratios, they caution against viewing this as a predictive tool. The complexity of genetics and maternal biology means that such tendencies can vary widely. The potential implications extend beyond curiosity; understanding these trends may influence future discussions about reproductive health and family planning, especially as parental demographics shift.