Background: Ultrasonography is essential in the prenatal diagnosis and care for the pregnant mothers. However,the measurements obtained often contain a small percentage of unavoidable error that may have serious clinicalimplications if substantial. We therefore evaluated the level of intra and inter-observer error in measuring mean sacdiameter (MSD) and crown-rump length (CRL) in women between 6 and 10 weeksâ gestation at Mulago hospital.Methods: This was a cross-sectional study conducted from January to March 2016. We enrolled 56 women with anintrauterine single viable embryo. The women were scanned using a transvaginal (TVS) technique by two observerswho were blinded of each otherâs measurements. Each observer measured the CRL twice and the MSD once for eachwoman. Intra-class correlation coefficients (ICCs), 95% limits of agreement (LOA) and technical error of measurement(TEM) were used for analysis.Results: Intra-observer ICCs for CRL measurements were 0.995 and 0.993 while inter-observer ICCs were 0.988 for CRLand 0.955 for MSD measurements. Intra-observer 95% LOA for CRL were ± 2.04 mm and ± 1.66 mm. Inter-observer LOAwere ± 2.35 mm for CRL and ± 4.87 mm for MSD. The intra-observer relative TEM for CRL were 4.62% and 3.70% whereasinter-observer relative TEM were 5.88% and 5.93% for CRL and MSD respectively.Conclusions: Intra- and inter-observer error of CRL and MSD measurements among pregnant women at Mulagohospital were acceptable. This implies that at Mulago hospital, the error in pregnancy dating is within acceptablemargins of ±3 days in first trimester, and the CRL and MSD cut offs of â¥7 mm and ⥠25 mm respectively are fit for diagnosisof miscarriage on TVS. These findings should be extrapolated to the whole country with caution. Sonographers can achieveacceptable and comparable diagnostic accuracy levels of MSD and CLR measurements with proper training and adherenceto practice guidelines.Keywords: Mean sac diameter, Crown-rump length, Measurement error
