探讨胎儿心轴（CA）在心动周期的变化特征及其在诊断胎儿先天性心脏病（CHD）中的价值。

选取2017年2月至4月在浙江大学医学院附属邵逸夫医院中晚孕期接受超声心动图检查的胎儿265例，其中，健康对照组197例，CHD组68例。分别测量每位胎儿收缩期心轴（CAS°）和舒张期心轴（CAD°），健康对照组组中孕组与晚孕组CAS°与CAD°参数、健康对照组与CHD组组间CAS°与CAD°参数比较，采用独立样本t检验。根据国际妇产科超声学会（ISUOG）的实践指南标准：健康胎儿CA正常参考值范围为（45±20）°，定义<25°和（或）>65°为胎儿CA异常，健康对照组与CHD组间CAS°与CAD° CA异常（<25°或>65°）占比比较，采用χ²检验。

对健康对照组197例与CHD组68例的孕妇年龄及孕周进行比较，差异无统计学意义（P>0.05）；健康对照组中胎儿的CAS°与CAD°随中晚孕孕周的增大，差异无统计学意义（P>0.05）。健康对照组CAS°为（40.88±10.27）°，CAD°为（35.07±9.44）°，差值为（5.85±4.42）°；CHD组CAS°为（44.34±15.03）°，CAD°为（41.32±16.71）°，差值为（5.01±3.52）°，差异均有统计学意义（t=-2.11、-3.79，P均<0.05）。197例健康胎儿中CAS°异常者11例（CAS°减小4例，CAS°增大7例），所占比例为5.6%；CAD°异常者27例（CAD°减小26例，CAD°增大1例），所占比例为13.7%。CHD组68例中CAS°异常者10例（CAS°减小4例，CAS°增大6例），所占比例为14.7%；CAD°异常者17例（CAD°减小12例，CAD°增大5例），所占比例为25.0%。健康对照组收缩期CA异常率与舒张期CA异常率明显低于CHD组，差异均有统计学意义（χ²=5.765、4.675，P均<0.05）。

CA的测量对胎儿CHD的超声诊断有重要意义，可作为胎儿CHD超声诊断的常规检查技术之一。

To investigate the cardiac axis changes within the cardiac cycle of both normal fetuses and fetuses with congenital heart diseases (CHD), and construct reference range of cardiac axis for normal fetuses.

Two hundred sixty-five fetuses were enrolled in our study, of whom 197 were normal fetuses and 68 were fetuses with CHD. The cardiac axis was measured at end systole (CAS°) and at end diastole (CAD°) in each case. Subsequently, all parameters were compared between the normal and CHD groups. The independent t-test was used to compare CAS° and CAD° parameters between the healthy control group and the middle pregnancy group and the late pregnancy group, and between the healthy control group and the CHD group. According to the practice guideline the International Society of Ultrasound in Obstetrics and Gynecology (ISUOG): the normal reference range for normal fetal cardiac axis was (45±20)°, with<25° and/or>65° defined as abnormal fetal cardiac axis. The Chi-square test was used to compare the proportion of CAS° and CAD° CA abnormalities between the healthy control group and the CHD group.

No significant difference was observed in comparison of maternal age and gestational age between 197 healthy controls and 68 CHD controls (P>0.05). There was no significant difference between CAS° and CAD° of the fetus in the healthy control group with the increase of the second and third gestational weeks (P>0.05). The mean cardiac axis in control group was (40.88±10.27)° at end systole, and (35.07±9.44)° at end diastole, resulting in an average difference of (5.85±4.42)°. While the mean cardiac axis in fetuses with CHD was (44.34±15.03)° at end systole and (41.32±16.71)° at end diastole, resulting in an average difference of (5.01±3.52)°. Significant difference was observed between two groups (t=-2.11,-3.79, all P<0.05). Among 197 normal cases, there were 11 cases with abnormal CAS° (4 cases with decreased CAS° and 7 cases with increased CAS°) accounting for 5.6%. There were 27 cases with abnormal CAD° (26 cases with decreased CAD° and 1 case with increased CAD°), accounting for 13.7%. In 68 CHD cases, there were 10 cases with abnormal CAS° (4 cases with decreased CAS° and 6 cases with increased CAS°) accounting for 14.7%. There were 17 cases with abnormal CAD° (12 cases with decreased CAD° and 5 cases with increased CAD°) accounting for 25.0%. The abnormity rates of both CAS° and CAD° were significantly lower in normal group than in the CHD group. The difference was statistically significant (χ²=5.765, 4.657, all P<0.05).

Measurement of cardiac axis at end systole and at end diastole provides values in screening for fetuses with congenital heart disease, and can be used as a routine measurement tool.