Statistical Data on Pregnancy Test Timing

Testing for pregnancy when trying to conceive is a sensitive issue. The emotional toll of repeated negative results is hard to imagine for those who have not experienced it. At the same time, waiting throughout the luteal phase to know the outcome of your cycle can be agony. For these reasons, knowing when to expect reliable results is extremely important, both to preserve your emotional state and to save money by not testing too early.

A related issue concerns the likelihood of getting "false" negative results which stem from testing too early. To try to shed some light on these questions we calculated some statistics on the most recently completed charts at Fertility Friend. We are presenting our findings and a discussion of the results below.

Method:
We considered a batch of the most recent charts analyzed on the FertilityFriend.com web site. We considered 93,184 recent charts for which the woman's averages from past cycles were available (most notably the average luteal phase length). For each chart considered we took note of the ovulation day, the first positive pregnancy test, the first negative pregnancy test and the average luteal phase length. From the ovulation day and the average luteal phase length we were able to calculate the day of the expected menstrual period. This latter parameter is extremely important to understand the results.

Results:

The graphs below represent the distribution of positive tests with respect to the day of the expected period, where 0 represents the day of the expected period:

Discussion:
Our data do not indicate the type of pregnancy test used (sensitivity is indeed an important parameter although most people tend to use the most sensitive tests) and a very small number of the results recorded as positive pregnancy tests may be actually the results of blood tests. Nonetheless, the results of our findings lead to very interesting conclusions.

As one could have expected, testing too early greatly increases your chances of a "false" negative. The average DPO at which people start testing (around 10 DPO) is probably related to some very optimistic advice and the strong desire to learn of positive results early. It is true that pregnancy tests can turn positive early (blood tests especially), however, it is rare with HPTs and is not something that should be relied upon within the emotional context of the trying to conceive journey. Further, we suspect that the frequency of early "false" negatives is actually higher than the 17% reported as many negative results go unreported.

The most interesting result is the nearly perfect match between the average first positive test result day and the day of the expected period. The average day to get a positive test is at 13.6 DPO and the average luteal phase length is 14 days (verified on our sample as well). This result can also be the consequence of the instructions given for testing, however, the distribution shows clearly that the maximum probability is almost exactly on the day the period is expected.

One remarkable figure in these statistics is the percentage of negative test results taken before the expected period day on non pregnant charts. This figure represents the proportion of women who tested too early and were not pregnant. In other words, this is the proportion of tests which may have been avoided. The number is high but probably underestimated still as we could expect very early negative tests to stay unreported because of the negative connotation of the test.

In conclusion, we certainly cannot stress enough the need to wait for a reasonable test date before spending your emotional (and financial) capital on early tests and lab procedures. This is certainly easier said than done. As with most sensitive emotional decisions, it is really up to you to decide what you can withstand. It is really a matter of weighing your desire to know early versus the disappointment, anxiety, and ambiguity that can be associated with seeing negative, or potentially "false" negative results. Keeping in mind that even cycles with perfectly timed intercourse often do not result in pregnancy, it is certainly something where understanding of the situation plays a great role. The Fertility Friend charting system proposes you a test date in full agreement with the results described above. We recommend as much as possible to actually wait until the test date.