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

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. Key words: Brain; Growth and development; Magnetic resonance imaging; Sex factors; Prenatal diagnosis