Have mothers who are trying to conceive ever carefully considered this question: Should I give birth in spring, autumn, summer, or winter? Which season can be considered the "best season to have a baby"?
The magazine "Human Reproduction" says: Autumn is actually a better time to conceive!
For the purpose of research,
We recorded nearly 50,000 menstrual cycles.
Previous studies on the seasonal patterns of human reproduction primarily used birth data, not conception data. Therefore, these studies did not consider the seasonal patterns of people starting to conceive or experiencing miscarriages, and they ignored differences in gestational length, potentially leading to less accurate estimations of conception dates.
In this analysis, researchers assessed the impact of seasonal variation on people’s ability to conceive and conceive (the probability of getting pregnant within a menstrual cycle) and the degree of variability across different geographic regions, based on prospective data from two groups in North America and Denmark.
Researchers believe that the season for trying to conceive may depend on factors such as culture, while the season for conception is controlled by fundamental biological mechanisms that affect fertility.
The study included 14,331 women aged 21-45 who planned to conceive within 6 months (women who had been trying to conceive for more than 6 months were more likely to undergo certain infertility treatments). This included 5,827 women from the United States and Canada [data from an online pregnancy survey (PRESTO) at the Boston University School of Public Health (BUSPH)] and 8,504 women from Denmark [data from a prospective cohort study at Aarhus University, Denmark (SG; 2007-2011/SF; 2011-present)].
Researchers from BUSPH and Aarhus University in Denmark conducted detailed investigations of these women's menstrual cycles every two months, collecting other information such as basic information (age, education, income), lifestyle habits (sports activities, smoking, drinking), medical records (height, weight, medication use), and reproductive status (childbirth, frequency of sexual intercourse) until they became pregnant or had completed 12 menstrual cycles of trying to conceive.
A diagram illustrating the menstrual cycle date information in the accessed questionnaire.
a) Women who completed the follow-up questionnaire in full b) Women who did not complete the follow-up survey in full
Data was collected from participants' self-reported and estimated menstrual cycle dates to predict the menstrual cycle in which pregnancy is likely. Participants also reported whether they had experienced a miscarriage since their last survey. If they were not pregnant, they were asked to state whether they were still trying to conceive.
Researchers tracked 48,795 menstrual cycles of 14,331 women.
The follow-up study ultimately found that 77% of the women became pregnant, with 69.8% of PRESTO participants and 82.3% of SF/SG participants. This may be related to factors such as their lifestyle habits. For example, compared to SF/SG participants, PRESTO participants had higher BMIs and lower levels of physical activity.
This doesn't seem to have anything to do with the season, does it? Don't worry, this isn't the end of the story.
Researchers also proposed two models: one adjusted based on the start time of conception, and the other adjusted for both the start time of conception and seasonal variations. The results from the two models showed no significant difference.
The study ultimately found that couples in North America and Denmark conceive more quickly in late autumn and early winter, especially in the southern states.
Although couples in North America and Denmark typically begin trying to conceive in September, they are most likely to get pregnant in late November and early December, especially in lower latitude regions.
So pregnancy and autumn go hand in hand?
In the United States, the peak of birthday celebrations occurs in early September, but in the northern states—and Scandinavia—this peak comes earlier, in the summer or even spring.
Compared to Danes, North Americans are more likely to start trying to conceive in the fall.
Dr. Wesselink believes that couples may schedule pregnancy for a variety of reasons, including work schedules (such as more flexible summer work hours), comfort (such as avoiding pregnancy in the hot months), or personal choices (such as wanting a fall baby).
However, this new study by BUSPH suggests that while there are many reasons why birthday months are popular, the season itself may have some influence on how easy it is to conceive.
After taking into account various factors, the study found that the season does indeed affect the conception rate of North Americans.
In the fall, conception rates in North America increased by 16%, while in Denmark they only saw an 8% increase; both types of countries experience a decline in conception rates during the spring. This seasonal effect is particularly pronounced in the southern states of the United States, reaching 45%, with conception rates peaking quickly in late November.
Meanwhile, the relationship between season and conception rate is similar in Denmark, the northern states, and Canada.
After controlling for seasonal variations in factors such as frequency of sexual intercourse, sugary beverage intake, smoking, and drug use, the results showed no significant changes.
“Many studies have investigated patterns in birth seasons, but they haven’t considered when couples start trying, how long it takes to conceive, or how long the pregnancy lasts,” said Dr. Amelia Wesselink, a specialist in epidemiology at BUSPH and the study’s first author. “After taking into account the seasonal patterns of when couples start trying to conceive, we found that fertility rates decline in late spring and peak in late autumn.”
Interestingly, this connection is more pronounced among couples living in low-latitude regions.
Dr. Wesselink believes that although this study cannot determine the cause of seasonal variations in conception rates, it can lead to several hypotheses about how seasonal variations affect fertility, including meteorological variables such as temperature and humidity, vitamin D intake, and environmental exposures such as air pollution.
However, it remains to be seen whether the results of this study are applicable to the Chinese population. There is also relatively little research on this topic in China, so it is difficult to draw a unified conclusion.
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