The First Hospital of China Medical University initiated a multi-center study on the reference range of echocardiography in Chinese Han Pregnancies to determine the reference range of echocardiography in the pregnant population and to promote the clinical application of echocardiography in the pregnant population, thereby offering the value of early evaluation and early diagnosis for cardiac structure and function in the pregnant population.

During normal pregnancy, the cardiovascular system of pregnant women will undergo significant adaptive changes in response to the growth of the uterus, fetus and placenta. Cardiac output and plasma volume will increase by 40% to 50% compared with non-pregnancy. The heart rate continues to increase, while the blood pressure decreases in the first and second trimesters and increases in the third trimester. The heart structure of pregnant women also remodels during pregnancy and the inner diameter of the cardiac cavity and myocardial mass increase. The above changes usually return to pre-pregnancy levels within 3-6 months after delivery. Pregnancy can change hemodynamics and cardiac structure, thereby causing corresponding changes in maternal cardiac function.Therefore, it is very important to closely monitor the changes of pregnant women's cardiac structure and function during pregnancy to assess their adaptive changes.

In addition, the incidence of cardiovascular disease in pregnancy is 1-4% worldwide, and about 15% of maternal deaths are caused by complications related to cardiovascular diseases during pregnancy. In China, the proportion of maternal deaths caused by cardiovascular diseases during pregnancy is increasing yearly and cardiovascular diseases during pregnancy have become the primary cause of death for critically ill pregnant women. Previous studies have shown that common complications during pregnancy, such as gestational hypertension and diabetes, can also alter maternal heart function. Therefore, early detection of changes in left ventricular systolic function of pregnant women during pregnancy and after childbirth, timely treatment and early evaluation of treatment efficacy can greatly reduce their mortality.

Echocardiography is the preferred method for cardiac examination during pregnancy, because of its safe and convenient, and has no radiation risk to the mother and fetus. It can accurately and quickly measure and evaluate the size of the pregnant woman's heart cavity, hemodynamic changes and cardiac function, and reflect the adaptive changes. Continuous observation at different stages of pregnancy and postpartum can deeply reveal the changing of cardiac structure and function. However, due to the adaptive changes during pregnancy, the reference value of normal adult echocardiography cannot be directly applied to pregnant women in clinical practice. At present, there is still a lack of normal reference value of echocardiography for pregnancies in clinical practice.

In conclusion, in order to assess the cardiac changes of pregnancies more comprehensively and accurately, and find the pathological changes caused by cardiovascular diseases during pregnancy timely, it is urgent to establish the normal reference value of echocardiography in pregnancies. The purpose of this study is to establish the normal reference value range of echocardiography in Chinese Han pregnancies in different pregnancy periods and early postpartum period, and to explore the influencing factors of changes with gestational age.

Inclusion Criteria:

• Han nationality;
• 18-45 years old;
• Basal body mass index before pregnancy < 30 kg/m2;
• Normal blood pressure (139-90/89-60 mmHg);
• No history of cardiovascular and respiratory diseases;
• No abnormal findings in the physical examination of the cardiovascular and respiratory systems;
• Normal results in blood, urine, fasting blood glucose, blood lipids, liver and kidney function, thyroid function and electrocardiogram;
• Echocardiography shows normal cardiac function with no structural heart diseases;
• No use of medications that affect the cardiovascular system.

Exclusion Criteria:

• Anemia (hemoglobin < 90 g/L);
• Other serious diseases of the immune, respiratory, digestive, nervous, urinary, blood, endocrine and other systems;
• Tumors;
• The poor quality of ultrasound images cannot meet the requirements of parameter measurement and analysis.

A total of 680 singleton pregnant women in the first trimester, who had normal results in various examinations and experienced regular obstetric examinations throughout the pregnancy, were selected from the obstetric outpatients in 34 centers, with 20 cases in each center.