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Abstract
F
etal biometry is of great interest in obstetric practice. It is helpful in the estimation of gestational age especially in women who do not remember the dates of their last menstrual period or whose fundal height on abdominal examination does not correspond to dates. The practice of assessing gestational age in early gestation is valuable in detection of growth aberration in later stages of pregnancy. In addition, fetal biometry distinguishes normal from abnormal fetal structures.
The BPD has traditionally been the most widely used ultrasound parameter in the estimation of gestational age.
The size of the cerebellum or transverse cerebellar diameter (TCD) is also important because it is a useful biometric parameter in estimating gestational age (GA) in the second trimester. Indeed, in some cases with dolichocephaly or brachycephaly, TCD may be a more reliable predictor than biparietal diameter (BPD), since the posterior fossa is not affected by external pressure, which may induce distortion of the fetal head. Because TCD seems unaffected by intrauterine growth restriction (IUGR) measuring TCD is especially advantageous when IUGR is suspected or when GA is uncertain.
Twins are two offspring resulting from the same pregnancy, usually born in close succession. Twins are either monozygotic (MZ) or dizygotic (DZ). In the former case, a single fertilized ovum splits into two distinct individuals after a variable number of divisions. Such twins are almost always genetically identical and therefore of the same sex. On the other hand, when two separate ova are fertilized, DZ twins result. These individuals are as genetically distinct as any other children born to the same couple. Sets of DZ twins may have the same or opposite sex.
The transcerebellar diameter nomogram obtained at 16-24 gestational weeks shows the same difference with worldwide use.
The singleton transcerebellar (TCD) nomogram is reliable and accurate in twins irrespective of placental chorionicity.
The present study was designed to compare the accuracy of transcerebellar diameter (TCD) measurement with biparietal diameter (BPD) in twin and singleton pregnancies with established menstrual dates.
This cross-sectional study included 200 pregnant ladies (100 singleton and 100 twin pregnancy) with sure and reliable dates at Ain Shams University Maternity Hospital in the period starting from January 2009 seen at 20 – 26 weeks pregnancy subjected for history talking with emphasis of the date of last menstrual period to ensure reliability, general and abdominal examination, informed consent and ultrasound. To confirm chorionicity, amnionicity and to measure the transcerebellar diameter (TCD) and biparietal diameter (BPD) for determination of gestational age.
The results of the present study proved that the transcerebellar diameter (TCD) is more accurate than the biparietal diameter (BPD) for determination of gestational age in singleton and twin pregnancies irrespective the chorionicity.
So we recommend the standardization of the use of the TCD as a part of the basic biometry in all singleton and multiple pregnancies.