There are other clues which can tell you how many weeks pregnant you are, but they’re not as accurate. You might be able to detect your baby’s heartbeat with a doppler scan at nine or 10 weeks’ gestation and you might feel the first foetal movements when you're between 18 and 22 weeks pregnant.
However, these pregnancy milestones are unreliable, as some women don’t feel any movement until they're more than than 22 weeks pregnant and dopplers rely on the position of the baby to pick up the heartbeat.