- The late summer baby boom is well known – due to a spike in conception at Christmas
- Experts say the increase in sex during holidays explains only a small part of the trend
- READ MORE: How popular is YOUR birthday? Find out in our interactive graph
The baby boom at the end of August is a well-known phenomenon.
During the holidays you are more likely to sit by the fire with your partner and are less likely to go outside in the cold.
This could mean more time to conceive.
However, research shows that the baby boom is not because you have more sex.
Instead, there may be a biological component to the increase in baby-making during the holidays.
Research shows that the holidays are the best time to get pregnant due to healthier sperm and increased testosterone
This map shows that holidays – including Christmas Eve, Christmas Day, New Year's Day and the 4th of July – are the least likely days for births
There is some evidence that this could be because sperm prefer colder temperatures.
A survey in the journal Obstetrics and Gynaecology showed that sperm quality improves in winter compared to summer.
The researchers found that men with normal sperm production had the healthiest sperm in winter and early spring, producing 70 million sperm per milliliter of semen, compared to 68 million in late spring.
Sperm produced in winter were faster than their counterparts in spring. According to the study, five percent of winter sperm were faster than baseline, compared to three percent in spring.
Sperm is more likely to reach a woman's egg faster, leading to a greater chance of becoming pregnant.
In addition, the woman's egg, a mature female reproductive cell, becomes more receptive to sperm at this time of year.
“Based on our results, (normal) sperm will perform better in winter, while cases of infertility associated with low sperm count should be encouraged to choose spring and autumn,” the researchers wrote.
Moreover, a 2021 Koren study of police officers in their 40s and 50s found that they had the highest testosterone levels in the fall and winter, while the lowest were in January and May.
The team found that testosterone levels were affected by temperature and the amount of daylight.
Testosterone is a male sex hormone that is mainly produced in the testicles. However, testosterone receptors are distributed throughout the body.
It helps maintain bone density, fat distribution, muscle mass, facial and body hair, sex drive and sperm production, according to the Mayo Clinic.
It also leads to a better chance of becoming pregnant.
However, other research shows that increased daylight hours may be associated with higher ovulation rates. This means that you are more likely to become pregnant on longer days, namely between June and September.
The time of year can also affect the baby's health. a Study from 2013 found that babies conceived in May were 13 percent more likely to be born prematurely, and on average were born a week earlier.
According to the study, gestational age (the amount of time a fetus stays in the womb) steadily decreased from January to May, before returning to normal levels in June.