中晚孕期正常胎儿颅脑发育常用生物学指标的MRI测量及分析

MRI measurement for normal fetal brain biometric parameters in second and third trimesters

目的分析MRI测量中晚孕期正常胎儿颅脑常用生长发育指标与胎儿性别的相关性，以及随孕周的变化规律，并探讨建立中晚孕期胎儿颅脑常用生长发育指标的MRI参考标准的可行性。方法对2012年6月至2017年4月在复旦大学附属妇产科医院进行产前MRI检查未见中枢神经系统异常的263例胎儿MRI资料进行回顾性分析。在MRI图像标准层面测量胎儿双顶径、枕额径、头围面积、小脑半球横径（transverse cerebellar diameter，TCD）、小脑蚓部前后径（anteriorposterior diameter of thevermis，APDV）、小脑蚓部高度（vermian height，VH）及小脑蚓部截面积（vermian cross-sectional area，VS），并计算胎儿头围以及（双顶径＋枕额径）／2。对各测量指标与胎儿性别进行Spearman相关分析，组间均值比较采用两独立样本t检验，并对各指标与孕周进行Pearson相关分析与回归分析。结果中晚孕期胎儿双顶径、枕额径及头围面积与性别相关（相关系数分别为-0．155、-0．149、-0．159，P值分别为0．032、0．038及0．027）。男性胎儿双顶径、枕额径、头围面积均大于女性[分别为（7．25±1．22）与（6．87±1．28）cm，（8．59±1．38）与（8．18±1．41）cm，（53．62±16．82）与（48．48±16．84）cm2，值分别为2．101、2．011及2．102，P值均〈0．051，男女胎儿均值差分别为0．38cm、0．41cm、5．14cm2。双顶径、枕额径、头围面积、头围、（双顶径＋枕额径）／2、TCD、APDV、VH及VS与胎儿孕周呈显著正相关（相关系数分别为0．950、0．947、0．962、0．957、0．957、0．976、0．931、0．943及0．960，P值均〈0．001），其中，TCD相关性最高（r=0．976），头围面积（r=0．962）、VS（r=0．960）次之。线性回归方程分别为：双顶径（cm）=0．276×孕周-0．453，R2=0．903；枕额径（cm）=0．308×孕周＋0．010，R2=0．896；（双顶径＋枕额径）／2（cm）=0．292×孕周-0．222，R2=0．916；头围（cm）=0．473×孕周-0．359，R2=O．916；头围面积（cm2）：3．795×孕周-52．232，R2=0．926；TCD（cm）=0．180×孕周-1．858，R2=0．952；APDV（cm）=0．047×孕周-0．353，R2=0．867；VH（cm）=0．071×孕周-0．592，R2=0．890；VS（cm2）=0．143×孕周-2．396，R2=0．919，P值均〈O．001。结论胎儿颅脑部分生物学指标与性别相关，对不同性别胎儿建立不同的参考标准有助于准确产前评估和诊断；中晚孕期胎儿双顶径、枕额径、头围面积、头围、（双顶径＋枕额径）／2、TCD、APDV、VH及VS均与孕周呈高度线性相关，可作为评估胎儿颅脑生长发育的良好指标；MRI定量测量胎儿颅脑生物学指标可为评估胎儿颅脑生长发育情况提供良好参考，建立胎儿颅脑生物学指标的MRI参考标准是可行的。

Objective To analyze the correlations of commonly used biometric parameters of normal fetal brain with fetal gender and gestational age （GA） and to evaluate the feasibility of establishing MRI reference standards for normal fetal brain biometry in second and third trimesters. Methods MRI measurements of 263 fetuses without central nervous system abnormalities were retrospectively collected from the Obstetrics and Gynecology Hospital of Fudan University from June 2012 to April 2017. MRI measurements of fetal biparietal diameter （BPD）, occipital-frontal diameter （OFD）, head circumference cross-sectional area （HCS）, transverse cerebellar diameter （TCD）, anterior-posterior diameter of the vermis （APDV）, vermian height （VH） and vermian cross-sectional area （VS） were obtained in every standard plane. Head circumference （HC） and （BPD＋OFD）/2 were calculated. Spearman correlation analysis, independent samples t-test, Pearson correlation analysis and linear regression analysis were used for statistic analysis. Results Fetal BPD, OFD and HCS were statistically correlated with gender in second and third trimesters （r= - 0.155, - 0.149 and - 0.159; P=0.032, 0.038 and 0.027）. The mean values of BPD, OFD and HCS of male fetuses were greater than those of female ones [（7.25±1.22） vs （6.87±1.28） cm, （8.59±1.38） vs （8.18±1.41） cm, （53.62±16.82） vs （48.48± 16.84） cm2; t=2.101, 2.011 and 2.102; all P〈0.05] and the mean differences between them were 0.38 cm, 0.41 cm and 5.14 cm2, respectively. BPD, OFD, HCS, HC, （BPD＋OFD）/2, TCD, APDV, VH and VS were positively correlated with gestational age （r=0.950, 0.947, 0.962, 0.957, 0.957, 0.976, 0.931, 0.943 and 0.960, respectively; all P〈0.001）. Among them, TCD （r=0.976） was the closest relating factor, followed by HCS （r=0.962） and VS （r=0.960）. The linear regression equations were as follows： BPD （cm）=0.276 × GA - 0.453, R2=0.903; OFD （cm）=0.308 × GA＋0.010, R2=0.896; （BPD＋OFD）/2 （cm）=0.292 × GA - 0.222, R2=0.916; HC （cm）=0.473 × GA - 0.359, R2=0.916; HCS （cm2）=3.795 × GA - 52.232, R2=0.926; TCD （cm）=0.180 ×GA - 1.858, R2=0.952; APDV （cm）=0.047 × GA - 0.353, R2=0.867; VH （cm）=0.071× GA - 0.592, R2=0.890; VS （cm2）=0.143×GA - 2.396, R2=0.919, all P〈0.001. Conclusions Some fetal brain biometric parameters are correlated with fetal gender. It is essential and conducive to establish different reference values for male and female fetuses to achieve accurate prenatal evaluation and diagnosis. Fetal BPD, OFD, HCS, HC, （BPD＋OFD）/2, TCD, APDV, VH and VS have strong linear relationship with gestational age in second and third trimester and can be served as good indicators for evaluating fetal brain growth and development. MRI quantitative measurement of fetal brain biometric parameters can provide more reliable reference data for prenatal evaluation of fetal brain growth and development. It is feasible to establish MRI reference standards for fetal brain biometry.