>>509363433ChatGPT o4-mini-high:
No. High-quality evidence does not support those claims:
Timing of intercourse and sex ratio
A large multicenter prospective study of nearly 950 births found no significant variation in the male-to-female ratio based on intercourse timing relative to ovulation (sex ratio ~101.5M/100F, versus expected 105M/100F; no consistent trend with “early” vs. “late” intercourse)
pubmed.ncbi.nlm.nih.gov
. A meta-analysis of natural-family-planning users likewise concluded timing cannot be used to affect offspring sex
pubmed.ncbi.nlm.nih.gov
sciencedirect.com
.
Y-sperm “fragility” vs. X-sperm hardiness
The Shettles method hypothesizes that Y-bearing sperm are faster but more fragile than X-bearing sperm, and that acidic or oxidative environments selectively impair Y-sperm. Morphological studies confirm slight size differences between X- and Y-sperm, but direct experimental evidence that Y-sperm are substantially more vulnerable to biochemical or oxidative stress in vivo is lacking, and no consistent clinical data validate differential survival under stress
en.wikipedia.org
.
Parental stress and sex ratio
Some population-level studies report acute stressors (natural disasters, epidemics) correlate with modest declines in male births (e.g. Trivers–Willard–type effects), but results are inconsistent. A systematic review found maternal stress sometimes alters sex ratio at birth, yet many long-term datasets show no significant association
pubmed.ncbi.nlm.nih.gov
nature.com
.
US presidents and daughters
It’s true that several U.S. presidents since Eisenhower have had only daughters (e.g., Johnson, Nixon, Clinton, G.W. Bush, Obama)
en.wikipedia.org
, but that reflects random variation in a small sample, not a biological bias.