I've been on implanon for about 6 months now and I no longer get my period at all. Ive heard that it is possible to get pregnant while on implannon, but I've known some people that have gotten pregnant without even knowing about it. And also that if your on implanon it can cause pregnancy test to come up negative so if I were to get pregnant and showed no signs and I'm alrready not getting my period, how would I know.

I am also on Implanon and have not had my period since I had it put in.

No birth control is 100% safe except for abstinence.

If you suspect you may be pregnant take a pregnancy test, or go to your doctor for a blood test.

Here is a site detailing some pregnancy symptoms.
Just remember though a lot of these symptoms can be caused by things like stress or hormone imbalances so it's just an idea.

Pregnancy Symptoms - Early Signs of Pregnancy : American Pregnancy Association

I haven't heard of anyone getting pregnant on Implanon... I am too on it and I havne't had a period since I have been on it. I love that. The only thing I don't like is the fact that I have gained weight.

Also... The first month I was on Implanon, I felt very pregnant and the fact that I haven't had a period was scary, but I know that I am not. It could just be the hormones.

Even though you would come up negative through pregnancy tests (the hormones cause that to happen) you could still be pregnant. Even if you were to go to a dr the test would come out negative, the hormones. The only way to know is to have it taken out and then take a test. Signs to look for though are increased breast size and sensitized senses. Hope this helps

I have had the implanon since march of 2008. I had my period not once until this last month (November of 2009). It did not make me gain weight or have any side effects. I have had unprotected sex with my partner for the past year and have yet gotten pregnant. I think not having your period while on the implanon is just normal for some girls. I don't think you have anything to worry aobut.