Baby, it’s hot outside

Women undergoing in-vitro fertilization (IVF) are significantly more likely to have a successful birth when their eggs are harvested during the summer or on an especially sunny day, according to a peer-reviewed study published last week in Human Reproduction.

🔢 By the numbers… Australian researchers analyzed data from 3,657 frozen embryo transfers performed by a clinic in Perth over an eight-year period.

What they discovered:

• Embryos collected during the summer months had a 31% chance of resulting in a successful birth – 30% higher than eggs retrieved in the fall.
• Embryos collected on days with 10.5+ hours of sunshine in Perth were 28% more likely to succeed than eggs collected on days with fewer than 7.5 hours of sunshine (regardless of the season).

The researchers say the stark contrast could potentially be explained by differences in activity, diet, and lifestyle across the seasons, or by environmental factors like pollutant density.

And it’s not just in Australia – a 2022 IVF study from the Northern Hemisphere (Boston) found embryos collected in the summer were 42% more likely to result in a successful birth than eggs collected during winter.

☀️❄️🫄 Zoom out: Seasonal changes affect more than just IVF-induced pregnancies. According to previous research, the season in which humans are born has a measurable effect on their future chances of developing certain medical conditions and behaviors. For example:

• Winter babies are more likely to be diagnosed with schizophrenia or bipolar disorder, while summer babies are less likely.
• Spring babies are more prone to developing depression, while the opposite is true for fall babies.
• Males born in the fall are more likely to become heavy smokers, as are females born in the winter.