A 14-week fetal heart rate of 143 does not determine whether the fetus is a girl or a boy. Fetal heart rate is the heart rate of the fetus, and the normal heart rate is between 110 beats per minute and 160 beats per minute. In the early stages of pregnancy, the fetal heart rate is usually fast, and can reach more than 160 beats per minute, which is a normal phenomenon. Fetal heart rate has nothing to do with the sex of the fetus and cannot be used to determine whether the fetus is a boy or a girl. Furthermore, the fetal heart rate varies from time to time and may increase after eating or exercising. The sex of the baby can be determined by ultrasound or DNA testing, not by the fetal heart rate. It is also important to note that any non-medical sex determination is illegal and is not medically necessary in clinical practice.