Comparison between transcerebellar diameter with biparietal diameter of ultrasound for gestational age measurement in third trimester of pregnancy

Transcerebellar diameter versus biparietal diameter for the measurement of gestational age in third trimester

Aim

To compare the accuracy of biparietal diameter and transcerebellar diameter in measuring the gestational age during the third trimester of pregnancy.

Material and methods

In this prospective observational study, 275 pregnant women with singleton pregnancy between 32 and 37 weeks gestational age were recruited from the outpatient clinics of both Helwan University Hospital and Ain Shams University Maternity Hospital, Cairo, Egypt, during the period from February 2021 to August 2021. Transcerebellar and biparietal diameters of the fetus were measured by a radiologist blinded to the women’s gestational age, and compared to the gestational age acquired from a reliable date of first day of last menstrual period.

Results

The gestational age calculated by first day of last menstrual period ranged from 32 to 37 weeks (34.35 ± 1.4), while estimated by transcerebellar and biparietal diameters ranged from 31 to 37 weeks (34.31 ± 1.39) and 31 to 39 weeks (34.32 ± 1.44), respectively. There was a strong positive correlation between gestational age and transcerebellar diameter (r = 0.98, p <0.001) as well as biparietal diameter (r = 0.87, p <0.001), yet a stronger correlation was with transcerebellar diameter. 93.6% of gestational age assessment by transcerebellar diameter was correct compared to only 79.9% by biparietal diameter.

Conclusions

Transcerebellar diameter is a reliable single sonographic fetal biometric parameter for the assessment of gestational age in third trimester of pregnancy.

Performance of late pregnancy biometry for gestational age dating in low-income and middle-income countries: a prospective, multicountry, population-based cohort study from the WHO Alliance for Maternal and Newborn Health Improvement (AMANHI) Study Group

BACKGROUND

We aimed to evaluate and improve the accuracy of the ultrasound scan in estimating gestational age in late pregnancy (ie, after 24 weeks' gestation) in low-income and middle-income countries (LMICs), where access to ultrasound in the first half of pregnancy is rare and where intrauterine growth restriction is prevalent.

METHODS

This prospective, population-based, cohort study was done in three LMICs (Bangladesh, Pakistan, and Tanzania) participating in the WHO Alliance for Maternal and Newborn Health Improvement study. Women carrying a live singleton fetus dated by crown-rump length (CRL) measurements between 8+0-14+6 weeks of gestation, who were willing to return for two additional ultrasound scans, and who planned on delivering in the study area were enrolled in the study. Participants underwent ultrasonography at 24+0-29+6 weeks and at 30+0-36+6 weeks' gestation. Birthweights were measured within 72 h of birth, and the proportions of infants who had a small-for-gestational-age birthweight (ie, a birthweight <10% of the standard birthweight for the infant's gestational age and sex according to the INTERGROWTH-21st project newborn baby reference standards) and appropriate-for-gestational-age birthweights were ascertained. Estimation of gestational age by standard fetal biometry measurements in addition to transcerebellar diameter (TCD) measurements was compared with gold-standard CRL measurements by use of Bland-Altman plots to calculate the mean difference and 95% limits of agreement. Statistical modelling was done to develop new gestational age prediction formulas for third trimester ultrasonography in LMICs.

FINDINGS

Between Feb 7, 2015, and Jan 9, 2017, 1947 women were enrolled in the study. 1387 pregnant women had an ultrasound scan at 24+0-29+6 weeks of gestation and 1403 had an ultrasound scan between 30+0-36+6 weeks of gestation. Of the 1379 unique infants whose birthweights were available, 981 (71·1%) infants were born with an appropriate-for-gestational-age birthweight and 398 (28·9%) infants were born with a small-for-gestational-age birthweight. The accuracy of late pregnancy ultrasound biometry using existing formulas to estimate gestational age in LMICs was similar to that in high-income settings. With standard dating formulas, late pregnancy ultrasound at 24+0-29+6 weeks' gestation was accurate to within approximately plus or minus 2 weeks of the gold-standard CRL measurement of gestational age, and late pregnancy ultrasound was accurate to within ±3 weeks of the CRL measurement at 30+0-36+6 weeks' gestation. In infants who were ultimately born small for gestational age, individual parameters systematically underestimated gestational age, apart from TCD, which showed minimal bias. By use of a novel parsimonious model formula that combined TCD with femur length, gestational age at the 24+0 -29+6-week ultrasound scan was estimated to within ±10·5 days of the CRL measurement and estimated to within ±15·1 days of the CRL measurement at the 30+0-36+6-week ultrasound scan. Similar results were observed in infants who were small-for-gestational-age.

INTERPRETATION

Incorporation of TCD and the use of new formulas in late pregnancy ultrasound scans could improve the accuracy of gestational age estimation in both appropriate-for-gestational-age and small-for-gestational-age infants in LMICs. Given the high rates of small-for-gestational-age infants in LMICs, these results might be especially relevant. Validation of this new formula in other LMIC populations is needed to establish whether the accuracy of the late pregnancy ultrasound can be narrowed to within approximately 2 weeks.

FUNDING

Bill & Melinda Gates Foundation.

The volume of the cerebellum in the second semester of gestation

Background and aims

The cerebellum ("little brain"), the largest part of hind brain, lies in the posterior cranial fossa, beneath the occipital lobe and dorsal to the brainstem. It develops over a long period: it is one of the first structures in the brain to begin to differentiate, but one of the last to mature. The use of ultrasonography has significantly improved the evaluation of fetal growth and development and has permitted prenatal diagnosis of a variety of congenital malformations.The aim of our study was to evaluate the cerebellar growth and development using 2 different measuring techniques: microMRI and ultrasound technique. The cerebellum measurements were related to gestational age.

Methods

We used 14 human fetuses corresponding to 15-28 gestational weeks, immersed in a 9% formalin solution. Magnetic Resonance Imaging (MRI) was performed by employing a Bruker BioSpec 70/16USR scanner (Bruker BioSpin MRI GmbH, Ettlingen, Germany), operated at 7.04 Tesla for cerebellar volume measurement. Ultrasonographic measurements of the cerebellum diameter were performed on 14 pregnant women, 15 - 28 gestational weeks. Ultrasound scan used 5-10 MHZ for transvaginal approach. Taking into consideration the values of the cerebellum dimensions and considering the general shape of the cerebellum as a transverse ellipsoid, the volume of the cerebellum was calculated by a mathematical formula for ellipsoid volume.

Results

The study correlates the measurements from the microMRI study with the ultrasounds data and the results are superposable. Both established the exponential volume growth after the 22-23 GW. We used the ellipsoid volume formula for the cerebellar volume using the half of the three diameters of the cerebellum determined by ultrasound measurements:Cerebellar Volume = Ellipsoid volume = 3/4 π r1 r2 r3.

Conclusion

There is a linear correlation between the microMRI measurements and ultrasound determinations. Based on all collected data we could apply an easy formula to calculate the volume of cerebellum, a useful criterion in the evaluation of the cerebellar development and the appreciation of the gestational age.