The answer to this question, unfortunately, has to be a very firm yes, it is possible to get pregnant on the one day a birth control pill has been forgotten.
In order for birth control pills to be effective, they have to be taken regularly, This means they have to be taken every day at the same time. Forgetting one, or even taking them at different times of the day, can result in pregnancy. So can vomiting or diarrhea if they occur within the first 30 minutes of taking the pill, as this is how long it takes for it to be absorbed into the bloodstream.
If a pill has been forgotten, the first thing to do is call the doctor and ask if it will be ok to take it later, or to take two the following day. This will work with some of them, but not all, as each pill is based on a different formulation. It is therefore absolutely necessary to check. Sometimes it is possible to get a so-called morning after pill.
In any case, as the function of the pills is based on being taken regular and missing one will upset the balance, it is best to use additional contraceptive methods for the rest of the month, just to be sure.
If it is too late to do anything about it, the only thing to do is wait and see. If the next period does not appear, a pregnancy test should be done as soon as possible; early home tests usually show up within a few days. It may still be negative, as the stress of worrying can easily delay a period. The sooner a pregnancy is confirmed, the sooner vital decisions can be discussed and made.
