The importance of information within arterial pulse waves has long been recognized in clinical medicine (Mohamed, 1872). Arterial pulse wave analysis has been employed widely in clinical practice, such as in cases of hypertension, cardiac failure, and ageing (O'Rourke, et al., 2001). Our previous studies revealed that the pulse spectrum of the radial arterial pulse could be highly correlated among patients with abnormal liver function (Wang, et al., 1996, Wang, et al., 1996). In addition, the specific Fourier components in the pulse provide more physiologic information than do systolic and diastolic blood pressure measurements during the process of dying (Kuo, et al., 2004, Kuo, et al., 2005). Recently, the fourth harmonic of the radial pulse wave has been shown to predict adverse cardiac events in asymptomatic patients with type 2 diabetes (Chang, et al., 2019)and pulse spectrum analysis has facilitated the diagnosis of coronary artery disease (Huang et al., 2019) One key method in Chinese medicine is using the harmonics of the arterial pulse to provide meridian information that can then be used to reveal a patient's physiologic and pathologic condition (Wang, et al., 2010).

In the clinic, the most dramatic physiologic event is pregnancy. Many documents discuss these issues in Chinese Medicine; for example, as stated in the bible of Chinese Medicine, Huang-Ti-Nei-Ching (1981),: "Normal pulse but appears weak, pregnancy" and "Significantly moving in Shaoyin (少陰) meridian, pregnancy." "Pulse Classics" (Wang, 2000) Another example is "Differential diagnosis of the Chi (尺), in which the pulse can detect the gender of the fetus, left larger than right is male; right larger than left is female." There is much information about pregnancy in pulse diagnosis, which has been practiced in clinics for a very long time. In fact, this practice has been used so long and so often that it has become difficult to determine the exact meaning and the accuracy of other practical approaches. Pulse diagnosis is the most important work to build the practicing definition of physiology, pathology, and diagnosis in the study of Chinese medicine.

In a previous study, we found that each organ and its related meridian are in resonance with a specific Fourier component of pressure wave (Wang, et al., 1994, Wang, et al., 1991). We also ascertained that the lower-frequency components were referred to as "Yin" and the higher ones as "Yang," and figured out the scientific meaning for the failure of hepatic, renal, or splenic Chi in the pulse (Kuo, et al., 2005). The meridian information gained through measuring the harmonics of blood pressure gives us qualitative and quantitative ways to realize the abstract statement in classic Chinese medicine. In the current study, we analyzed the blood pressure (BP) pulse of pregnant women to verify the information recorded with classic methods. We hypothesized that harmonics could be physiologic indicators corresponding with the gestation process. If we could find the relationship between harmonic information and pregnancy, we could confirm that the physiologic difference comes from the meridian, and could then precisely apply this information in the clinic.