Can birth control mess up LMP to know how many weeks along you are?
- LizBLv 71 month agoFavorite Answer
If you're not sure when your last period was (or more like "period" since on BC it's just withdrawal bleeding and not a real period), then yes, it can. Getting off BC to attempt TTC can also throw off your dates if you're lucky and conceive right away, since it can take a couple a month or two for your body to self-regulate back to your natural cycle.
If you're able to get in with your OB to do a dating ultrasound, that's actually the most accurate way of determining gestational age, more than LMP. In the first trimester it's accurate ± about 3 days, presuming the pregnancy is viable.
- Ranchmom1Lv 71 month ago
It's not common at all to conceive while on birth control (less than a 1 in 100 chance of conception). If a person does conceive, the pregnancy would have happened after the previous withdrawal bleed, so dating the pregnancy should be the same.