23 weeks pregnant. ob said i have 2nd placental lobe. they need to check to rule out pasa previa. what are chances of having it? said baby looks fine

Need US to see where: The placenta is. There are no "chances" - either the placenta is over the endocervical canal (placenta previa), is very close, or is clearly away from the endocervical canal.

Possible, unlikely: With a bilobed placenta, there is the chance that there can connecting vessels between the two lobes. The chance that these vessels are near the cervix is extremely low, but it must be ruled out. This is best done with a vaginal ultrasound. I cannot give you a statistic, but it can be evaluated.

Rare, but good call.: Sounds like your obstetrician knows his/her stuff! succenturiate lobe (paraplacenta) is not common but vasa previa is pretty rare even in the presence of two placental lobes. The risk of losing the baby, though, from undiagnosed vasa previa is so great that a thorough ultrasonographic examination is warranted by an experienced provider (maternal-fetal medicine). If present, vasa previa needs c/s!