The National Health Service (NHS), the UK’s biggest health website, recommends waiting until at least 12 weeks after giving birth to have a pap test. Pap tests during pregnancy are not recommended because according to the NHS pregnancy can make the result of the test harder to interpret and could be inaccurate (source).
The NHS deserves kudos for putting the health and safety of women and their unborn children ahead of opportunistic testing. Unfortunately this is not the case in other countries. Even though pregnancy can make it harder to get clear results, other countries are still recommending pap tests during pregnancy. WebMD, the most popular source of health information in the US, recommends having a pap test during pregnancy as part of “routine tests” that are “important for your health and your unborn baby’s health” (source).
In Canada, the Canadian Cancer Society states that a “Pap test done as part of routine care during pregnancy can find cervical cancer” (source). The Royal Australian and New Zealand College of Obstetricians and Gynecologists advise that “pregnant women can be reassured that a Pap smear does not cause any problems for their pregnancy” (source).
Anecdotal evidence aligns with recommendations of the NHS to not have a pap test during pregnancy, but for different reasons. According to some anecdotal evidence there may be a correlation between pap smears and miscarriage, and other evidence suggests pap tests during pregnancy may risk disturbing the mucous plug and lead to premature labor.
More on this topic: http://womenagainststirrups.proboards.com/thread/69/link-pap-smears-miscarriage