At 11 weeks and 3 days, a baby's heart rate of 171 beats per minute is generally considered normal. During the first trimester, the average fetal heart rate ranges from 110 to 170 beats per minute. As the pregnancy progresses, the heart rate tends to decrease slightly. However, individual variations are common, so there is no need to worry if your baby's heart rate falls within this range. It is important to remember that ultrasound measurements can have a margin of error, so it is always best to consult with your healthcare provider for a more accurate assessment. If you have any concerns or notice any other unusual symptoms, don't hesitate to reach out to your doctor for further evaluation and guidance.