Qualitest Pharmaceuticals is recalling several lots of its birth control pills because of a packaging error that could increase the risk of unplanned pregnancy.

Normally, birth control pills are packaged so that it is easy to see what order the pills should be taken in, but in about 1.4 million Qualitest packs, the orientation was reversed and the pills' lot numbers and expiration dates were not visible.

The orientation matters because four or seven pills each month are placebos, so that the woman can have her menstrual period. The placebos are supposed to be taken at the end of the month, but in the defective Qualitest packs, they were placed at the beginning.

The worst pill to miss in any pack of pills is the very first pill, Marjorie Greenfield, the division chief of obstetrics and gynecology at University Hospitals Case Medical Center in Cleveland, Ohio, told ABC News. And so now you're missing the first four or the first seven, so you will probably release an egg that month.

That means the risk of unintended pregnancy for women who used the defective packs was substantive, Greenfield said. When used correctly, birth control pills are between 96 and 99 percent effective, but taking pills at different times of the day or skipping days decreases their effectiveness drastically. Missing pills is a way that can totally fail, she said. Not that it fails a little -- it totally fails when you miss a few pills.

Ranit Mishori, an assistant professor of family medicine at Georgetown University, who is not affiliated with Qualitest, told ABC News on Friday that women who had taken pills from one of the affected packs should ask their doctor for an alternate product, use condoms or another backup form of contraception, and get a pregnancy test.

The 1.4 million defective packs were shipped to stores starting last year, so the number of women affected since then could be large.

The good news is that the placebo pills are usually a different color than the active pills, so a lot of women probably noticed that the placebos were in the wrong place before they took them.

The affected lots include Cyclafem, Emoquette, Gildess, Orsythia, Previfem and Tri-Previfem. Patients can call Qualitest at 1-877-300-6153 to find out if their birth control packs are among those being recalled.