Fertility Expert Explains How Sharna Burgess' Unexpected Pregnancy Happened - Exclusive

Sharna Burgess of "Dancing with the Stars" dropped a major bombshell in her Instagram Q&A this week: She and boyfriend Brian Austin Green are expecting their first baby.

According to People, a follower asked Burgess whether she and Green had been trying to conceive. "I was on birth control," she wrote. "We were thinking of trying mid to late this year lol. But the Universe made her own plan, found a window and went for it."

Birth control, unfortunately, can fail for any number of reasons. The major reason, Vox explains, is human error: people forgetting to take their birth control pills. Dr. Sophia Yen, Founder and CEO of Pandia Health, explained to The List exclusively that progestin-only birth control pills should be taken in the same three-hour window every day, while combination pills can be taken within a five-hour window. If you miss the window on your progestin-only pill any day, "you need emergency contraception" or you need to abstain from having sexing over the next five days.

Combination pills are a little more forgiving. According to Dr. Yen's website, however, issues come into play if you've missed three to five days of pills, especially if you miss in the first three weeks of your pill pack. "Depending on the type of birth control you're on," Pandia Health explains, "the period you take the sugar pills (placebo pills) can last anywhere from four to seven days." In that time, "you may not be protected from pregnancy."

The placebo pills, according to Vox, can be safely skipped if the user doesn't want to get their period. When they stop taking the pill, their normal period cycle will resume.

Whether Sharna Burgess used an oral contraceptive or not, a few factors other than time play into why it could have failed.

If she had been taking over-the-counter allergy medication, the efficacy of Burgess' birth control could have dropped. "I personally noticed that pseudoephedrine causes breakthrough bleeding," Dr. Sophia Yen exclusively told The List. "This is most likely because it revs up the liver and the liver eats through the birth control pills faster." Pseudoephedrine is most commonly known as Sudafed. According to Dr. Yen, St. John's Wart and activated charcoal, used most often if you need to get your stomach pumped, also puts you at risk for birth control failure.

But there could be another reason why Burgess ended up pregnant: her genes. In 2019, a new study was published that showed how metabolism factors into how protected a woman is by the birth control pill. According to Reuters, the study shows that some birth control users "may inherit genes that break down contraceptive hormones more rapidly," which keeps the hormone level of the pill you're on — progestin-only or a combination — too low to prevent pregnancy.

"Knowing that there is a difference in how people metabolize hormones sets the stage for more research that can help us ... give the right medication to the right patient," Dr. Anne Davis, an obstetrician-gynecologist at NewYork-Presbyterian/Columbia University Irving Medical Center told Reuters.

The problem with solving the mystery of Burgess' and many other pregnancies that happen despite birth control is that there still hasn't been enough research done to understand.