Sales of pregnancy tests typically soar in the first months of the year, as more women than usual tend to become pregnant -- or just think they are, according to Inverness Medical, the makers of the Clearblue Easy pregnancy tests.

Dr. Brad Imler, president of the American Pregnancy Association, stated that most births occur in August and September -- nine months after December and January. Furthermore, winter holiday months tend to be very stressful for women, and stress can cause women to miss their period -- often the first sign of pregnancy, Imler said.

He explained that the best way to distinguish a true pregnancy from a false alarm is to focus on additional symptoms of pregnancy. These include tender or swollen breasts, fatigue, nausea, headaches, backaches and a change in appetite.

Women who have just missed a period but don't feel anything else may not really be pregnant, Imler noted. "The absence of other pregnancy symptoms is probably the best clue that it is the stress of the holidays," he said.

Women often become stressed during the winter months for financial reasons, Imler said, when Christmas brings "additional needs for spending." Often, women are also responsible for the majority of the family's gifts, cards and parties, he noted, and some women in school may worry about end-of-semester exams.

In addition, many women start the New Year with a resolution to exercise more, and a big shift in activity -- such as going from no exercise to many workouts per week -- can cause periods to be delayed, missed or lightened, Imler noted. Changes in menstruation are not necessarily a sign that women are exercising too much, he added, as long as their periods return to normal within one or two months.

More women tend to also want to conceive during the holidays, Imler said in an interview, in order to spend most of their pregnancies in the winter, when they can largely stay indoors and relax. In winter, women also can get "caught up in the spirit" of the holidays, when they spend happy time with family and children.

Women who have questions about problems with menstruation -- and wonder whether they might be pregnant -- can call the American Pregnancy Association toll-free support line at 1-800-672-2296, Imler said. He added that the line typically receives 32,000 calls per year.