The first study of its kind shows when women are most likely to try to conceive and explores couples who get pregnant faster in the late fall and early winter. Birthdays worldwide reach their peak at the beginning of September. In Scandinavia, however, these are earlier - in summer or even spring. Although many factors likely contribute to the popularity of certain seasons, the different seasons themselves can play a role.
You are most likely to get pregnant
The study finds that while couples in North America and Denmark are most likely to start trying in September, they have the best chances of conceiving in late November and early December.
“There are many studies looking at seasonal patterns in births. However, these do not take into account when couples try to conceive or how long their pregnancies last.” This is what the lead author of the study, Amelia Wesselink, explains. She is a postdoctoral researcher in epidemiology.
“After accounting for seasonal patterns of when women become pregnant, we found a decline in fertility in late spring and a peak in late fall,” she says. “Interestingly, the association was stronger in couples living at lower latitudes.”
North Americans were more likely than Danes to attempt conception in the fall, perhaps in the hope of giving birth. During the summer there is less work. This could potentially be more important in the US than in Scandinavia.
However, taking these patterns into account, the season affected the fertility of North Americans by 16 percent. The Danes only saw a seasonal increase of 8 percent in the fall and a decline in the spring. In southern states, seasonal variation was even greater at 45%, with a peak in late November. In Denmark, the northern states and Canada the relationship between season and fertility was about the same.
Study results
The study used data on 14,331 women who had wanted to become pregnant for no more than six months. These included 5,827 US and Canadian participants and 8,504 Danish participants. This study followed women with detailed surveys every two months. Data was collected on everything from the frequency of sexual intercourse and menstruation to smoking and nutrition to education and income.
The results did not change significantly after controlling for seasonally varying factors, including frequency of sexual intercourse, sugary drink intake, smoking and medication use.
“Although this study cannot identify the reasons for seasonal variations in fertility, we are interested in exploring various hypotheses regarding seasonally varying factors and their effects on fertility, including meteorological variables such as temperature and humidity, vitamin D deficiency, and othersEnvironmental factors such as air pollution“, says Wesselink about themStudy.
