Care with a midwife can be started at the first sign of pregnancy to run a pregnancy test or lab work, order an ultrasound, and establish dates. Viable fetal heart tones can often be found with a doppler around 11 weeks.
Routine prenatal care then continues on a regular basis monthly to 28 weeks, every 2 weeks until 36 weeks and then weekly until the baby comes. Additional appointments will be made as needed and in the post dates period.
It is also acceptable to transfer into the care of a midwife midway though your prenatal period at any stage if your chosen midwife has availability. It is never to late to look into the option.