It is not uncommon for a fetal heartbeat to be undetectable at 12 weeks of pregnancy, especially if an abdominal ultrasound was used. In some cases, the position of the baby or the mother's body shape can make it difficult to hear the heartbeat. However, it is important to follow up with your healthcare provider as they have suggested. At your next appointment around 16 weeks, they will likely use a different method such as a transvaginal ultrasound or Doppler device to listen for the heartbeat more accurately. Remember that every pregnancy is unique and there can be variations in when the heartbeat becomes audible. Try not to worry too much until you have more information from your healthcare provider.