Fetal interlens distance: normal values during pregnancy.

OBJECTIVES: The aims of this study were to establish normal ranges of values for interlens distance (ILD) during gestation, and to assess the bivariate correlation between ILD and the growth of the bony structure of the eye, and other fetal biometric parameters. METHODS: A cross-sectional study of morphologically normal, singleton fetuses, was carried out in low-risk pregnant women. We measured the distance between the centers of the fetal lenses from 12 to 37 completed weeks of gestation. The anterior coronal section was used to measure the ILD. The biorbital diameter (BOD) was measured in the same plane. We analyzed the correlation ?between the ILD and gestational age (GA), BOD, biparietal diameter (BPD), head circumference (HC) femur length (FL), and abdominal circumference (AC). The fetal gender was assessed to evaluate possible significant differences. RESULTS: Four hundred and fifty normal fetuses were recruited for the present study. In 427 fetuses appropriate ILD measurements were obtained. In 377 fetuses complete evaluation of all parameters was accomplished. ILD demonstrated a high positive correlation with GA (r(2)=0.969), BPD (r(2)=0.959), HC (r(2)=0.962) AC (r(2)=0.949) and FL (r(2)=0.956) as pregnancy advanced. Mean BOD:ILD ratio was 1.50 (+/- 0.08), and presented a constant pattern during pregnancy (r(2)=0.006). No statistically significant differences were found between genders for mean ILD and GA (P = 0.604 and P = 0.595, respectively). CONCLUSION: The results of the present study confirm previous hypotheses regarding the close relationship between eyeball growth and the surrounding bony structures. We found a fixed BOD:ILD ratio of 1.5 throughout pregnancy. Therefore, the present chart of fetal ILD may reliably reflect the expected bony structure development, and may be used interchangeably with the axial plane of the BOD measurement, adding valuable simultaneous information regarding eyeball development. Moreover, ILD may be used as a complementary tool in the elaboration of various severe abnormalities, mainly related to craniofacial and nervous system malformations. Copyright (c) 2009 ISUOG. Published by John Wiley & Sons, Ltd.