The Twin Effect - Getting Pregnant After Birth Control Pills

The Twin Effect: Getting Pregnant After Stopping Birth Control Pills

Birth Control Pills and Twins
Having twins after taking birth control pills. Jonathan Nourok / The Image Bank / Getty Images

The Twin Effect

"My husband and I decided that I would discontinue the use of oral birth control and try to conceive. The first month after I stopped taking "the pill" I got pregnant. It was thirteen days after my first cycle had ended. I knew almost immediately that we were pregnant. I think it was about five days before my cycle should have started that I took a home pregnancy test. It was positive!!

We were elated!! At seven and a half weeks pregnant, we went to the doctor to have an ultrasound, low and behold, it showed TWINS!! They don't run in either family, so needless to say, it was a huge shock. That's when I was told that as soon as you stop taking the pill, you are at higher risk of conceiving multiples. Now that my fraternal twin boys are three months old, looking back, we would not have done anything different. They are WONDERFUL!!" -- Amanda

The Connection Between Twinning and Birth Control Pills 

Like Amanda, many women have heard about the "Twin Effect," a correlation between taking birth control pills and twinning. It is theorized that conceiving shortly after the discontinuing the use of birth control pills increases the chances of twins. While using birth control pills, ovulation is suppressed. When they are discontinued, it's thought that the ovaries can "rebound" and super-ovulate, releasing more than one egg in a cycle and increasing the opportunity to conceive dizygotic or fraternal twins.

The concept is primarily based on a 1977 study published in the New England Journal of Medicine that showed women who got pregnant shortly after stopping oral contraceptives were twice as likely to have twins. These twins were generally dizygotic (fraternal), rather than monozygotic (identical). Dizygotic twins form when two separate eggs are fertilized by two separate sperm, supporting the idea that the ovaries were releasing multiple eggs in response to the stoppage of contraceptive pills.

After being off the pill for several months, ovulation should return to a normal pattern of one egg per month, and the chances of twins are reduced to normal levels. 

The Twin Effect hasn't really been researched since that 1977 study in the New England Journal of Medicine so there are no additional studies to prove the existence of the relationship between birth control pills and twins. Anecdotally, many moms of twins -- like Amanda -- cite birth control pills as the reason they became pregnant with twins. However, there are many other causes of twins.

Other Causes of Twins

Genetics: It’s thought that some women just hyperovulate regularly, and that there is a gene that causes them to do so. Although both men and women carry the gene, only women ovulate. So a woman with the gene who hyperovulates may have fraternal twins. A man with the gene wouldn’t be more likely to have twins, but he may pass the trait to his daughter, and maybe she’d be a candidate to have twins.

Family History: It’s thought that women who have had conceived and borne several children already are more likely to have twins.

While the previous pregnancies don’t cause hyperovulation, or cause twins, it’s possible that the mother’s womb is just more hospitable to sustaining a twin pregnancy. 

Maternal Age: As a woman grows older, she is more likely to hyperovulate; perhaps it is the body’s accelerated attempt to reproduce before time runs out. Women over the age of 30 are more likely to have twins, and the rate increases even more after the age of 35. 

Height: Taller women have a higher than average rate of twin pregnancies. The reasons aren’t particularly specific, but perhaps it is because increased height is associated with better nutrition, or the additional height provides more “room in the womb,” making a multiple pregnancy more likely to thrive.

Race: Women of African descent produce a higher number of twins than women of Asian descent. 

Diet: High rates of twins have been found in cultures where the diet is rich in a type of yams that contain phytoestrogen. One example is the Yoruba tribe in Nigeria, which has the highest rate of twins of any population in the world. 

Sources:

Luke, B., and Eberlein, T. "When You're Expecting Twins, Triplets or Quads (3rd Edition)." Harper Collins, 2010. Print.

Minkin, M. J., and Wright, C. V. "A Woman's Guide to Sexual Health." Yale University Press, 2005. Print.

Rothman, K. "Fetal Loss, Twinning and Birth Weight after Oral-Contraceptive Use." NEJM, September 1, 1977, pg. 468.

Tinglof, C. "Double Duty: The Parents' Guide to Raising Twins, from Pregnancy through the School Years (2nd Edition)." McGraw-Hill, 2009. Print.

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