Cavum septum pellucidum nomogram during the second trimester of pregnancy.

This study aimed to determine cavum septum pellucidum (CSP) nomogram values between 15-28 weeks of gestation. Routine biometric measurements and CSP width were measured by transabdominal ultrasonography in 6042 structurally normal foetuses between 15-28 weeks of gestation. Distribution of CSP width by the week of pregnancy and percentile values were calculated. The mean week of gestation (GW) was 21 ± 1.7, and the mean biparietal diameter (BPD) was 50.2 ± 5.8 mm. The CSP width range was 1.6-7.7 mm at 15-28 weeks, and the mean CSP width was 4.1 ± 0.8 mm. CSP width was found to have a significant correlation between a gestational week (CSP = GW X 0.2705-1.6121; R = 0.62;  < .01) and BPD (CSP = BPD X 0.0859-0.273; R = 0.651; p 0.01). CSP width was found to differ significantly according to gestational weeks, and percentile distributions were calculated. Between 15 and 28 weeks of gestation, the 95th percentile values of CSP width were found to be 3.7-7 mm. Our study was determined that CSP width increased linearly between 15-28 weeks of gestation. For this reason, we think that it would be more appropriate to use CSP width percentile values in the examination of the foetus. Impact statement The cavum septum pellucidum can be easily identified and evaluated by ultrasonography after 18 weeks of pregnancy. CSP can be associated with severe brain anomalies if it is not visualised or deformed. Moreover; large CSP may be associated with chromosomal abnormalities. Our study showed that CSP width increased linearly between 15-28 weeks of gestation. CSP width was found to differ significantly according to gestational weeks, and between 15 and 28 weeks of gestation, the 95th percentile values of CSP width were found to be 3.7-7 mm. We reported that it would be more appropriate to use CSP percentile values according to the gestational week in the definition of abnormal CSP.