It can be a long, hard road for couples who are trying to conceive. But that road might become a little easier to navigate, thanks to fertility seasonality research by scientists at the University of Manchester in the UK, Queen's University in Canada, and Cryos International in Denmark.
Published in the peer-reviewed journal Reproductive Biology and Endocrinology, the study discovered that sperm quality is highest in the summer and lowest in the winter.
...seasonality affects male fertility more than temperature.
The highest quality sperm showed the same pattern of seasonal variation in two very different climates (Denmark and Florida), suggesting that seasonality affects male fertility more than temperature.
While conducting the study, all samples (taken from 15,581 men between the ages of 18 and 45 in Denmark and Florida) were analyzed within an hour using the same system to ensure consistency across all measurements.
Researchers also examined the outdoor temperatures during the month the sperm was collected as well as two months prior, when early sperm development begins.
In both Denmark and Florida, the fast‑moving sperm were most plentiful in June and July; the lowest in both locations were recorded in December and January.
On the fertility front
Bear in mind, just because sperm swim faster in June and July doesn't mean you're automatically more likely to conceive twins or higher-order multiples if you get pregnant in the summertime.
Multiple pregnancies are caused by factors like hyperovulation (releasing more than one egg in a cycle, leading to fraternal twins), a single fertilized egg spontaneously splitting (identical twins), undergoing fertility treatments, maternal age, and a family history of fraternal twins.
Having said that, multiple pregnancies can be linked to sperm motility and semen quality, so the chance of twins is always there. Studies by Danish fertility specialists have shown that fathers of non-identical (dizygotic) twins tend to have higher sperm motility and semen quality than fathers of singletons, which could be linked to multiple pregnancies.
Twinning can also be influenced by a father's level of insulin growth factor-2 (IGF-2), which is associated with cell growth and division. The IGF-2 level is partly heritable, and when it's transmitted to children by their fathers, it's active (the same gene transmitted by mothers is inactive).
So, it's possible that monozygotic (identical) twins could appear at a higher rate in some families if a higher level of the IGF-2 gene is being transmitted by the father.
Seasonal patterns can optimize outcomes
If you're trying to conceive or know someone who is struggling with this stage, show them the study and let them know that the best time of year to conceive could very well be summertime, as seasonality plays an important role in semen motility and quality.
Understanding the seasonal patterns uncovered by this research can allow you to optimize the timing of treatment and fertility testing, impacting the outcome when you're trying to conceive.
Did you conceive in June or July? If you did, was it a multiple pregnancy? Let us know in the Comments section below or connect with us on Instagram to share your thoughts!
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