What's the best time of year to get pregnant?

If you live in southern areas of the U.S., your chances of conceiving in that window of time are especially high, according to a studyOpens a new window published in the journal Human Reproduction. The researchers analyzed data on more than 14,000 women who had been trying to get pregnant for under six months. Almost 6,000 of the women were from the U.S. and Canada, and the rest were in Denmark. The women enrolled in the studies answered regular surveys to record their attempts to get pregnant and when or if they actually conceived (77 percent did during the study period), along with other information that could influence pregnancy such as diet and smoking. None of the women were getting fertility treatment.

Danish couples also had better luck getting pregnant in late fall, but the trend was weaker than in the U.S.

The study is one of the first to examine when women are most likely to conceive, rather than looking at when they're most likely to give birth. Births in the U.S. peak in August and September, the authors said, which lines up pretty squarely with this study's findings on when couples most commonly conceive.

So why is late fall such a fertile time for North American women? Well, that burning question will have to be answered by future studies. This one didn't investigate the reasons. But the researchers did have some theories.

"Although this study cannot identify the reasons for seasonal variation in fertility, we are interested in exploring several hypotheses on seasonally-varying factors and how they affect fertility, including meteorological variables such as temperature and humidity, vitamin D exposure, and environmental exposures such as air pollution," lead author Amelia Wesselink said.

In other words, human fertility may be influenced in some way by our environment. Other factors could be human driven, the authors wrote. For example, couples may plan pregnancies to coincide with periods of the year when they have more time off (such as the summer), or simply because they'd prefer to have a baby during a particular month.

The study relied on women reporting their menstrual cycles and attempts to get pregnant accurately in online surveys, so the results may not be completely foolproof.

Of course, there are many factors that can affect your chances and decisions around getting pregnant. For more information and tips on pregnancy planning, and how to get pregnant fast, visit BabyCenter's Getting Pregnant resources page.