The purpose of this study is to look at the statistics of early negative pregnancy tests (Commonly called BFN - Big Fat Negative in the community) when later followed by a positive pregnancy test (BFP - Big fat Positive in the community lingo) in the same cycle.
Particularly we are interested in looking at the statistics related to the timing of early negative results and the timing of a later positive result in the same cycle.
When seeing an early negative test result, most people wonder if they could still be pregnant and if they might test positive later on in the cycle. If a negative test was taken too early, the answer is most definitely, yes (Check the Chart Gallery for numerous examples). They could still be pregnant and just testing too early to see a positive result. It's interesting to look at some statistical data about these pregnancy test results.
To explore the issue of the reliability of early pregnancy tests, we looked at just under 6000 charts for which a negative pregnancy test was followed by a positive test and did not result in a miscarriage.
First Negative Pregnancy Test Before Positive
Average: 9.08 DPO (Days Past Ovulation)
Median: 9 DPO
This histogram represents the frequency distribution of first BFN when followed by a BFP. The cumulative histogram is displayed below:
By 11 DPO more than 80% of the negative have been accounted for.
First Positive Pregnancy Test After Negative
Average: 12.72 DPO
Median: 12 DPO
This histogram represents the frequency distribution of a first BFP (positive pregnancy test) when preceded by a BFN. The cumulative histogram is displayed below:
Discussion & Conclusions:
Not surprisingly, we have to wait for 14 DPO to see 80% of the positive tests accounted for. This is quite in line with a separate study that we conducted earlier although in this sample we have slightly earlier testing and most likely with more sensitive tests as well.
More interesting is the conclusion that we can draw from the BFN data. According to the community data, if you get a negative test beyond 11 DPO your chance of getting a BFP later on is significantly reduced. In other words, if you get a negative (BFN) before 11 DPO (Days Past Ovulation) there is still a good chance that you could get a positive later on.
It is also a reminder that if you can do so, you need to delay your testing as long as possible. Obviously though there are real reasons to have to test earlier beyond simple curiosity.
Symbol & Abbreviations:
BFN: Big Fat Negative, Negative Pregnancy Test.
BFP: Big Fat Positive, Positive Pregnancy Test.
DPO: Days Past Ovulation.