Small CRL (>2 SD below the mean) has been associated with small for gestational age infants and mGSD <50th percentile has been associated with chromosomal abnormalities. Aim: The present study aimed to find the correlation of the difference between mGSD and CRL and the first trimester pregnancy loss in low risk pregnancy. Methods: This is a prospective cohort that was carried out in the Outpatient Clinic of the Obstetrics and Gynecology Department, October 6 University Hospital. The study involved 100 pregnant women examined using 2D ultrasonography starting early in the first trimester with a first scan between 6 and 8 weeks. Another follow-up scan was conducted at 12 weeks. Outcome of first trimester was recorded. Result(s): Mean mGSD was 20.44 mm and mean CRL was 10.8 mm. Fetal loss in first trimester was reported in seven patients (8.8%) and 73 (91.2%) resulted in an ongoing pregnancy and entered the 2nd trimester successfully. There are statistically significant relations for incidence of fetal loss with body mass index, history of vaginal bleeding in current pregnancy, history of fetal loss and difference. Multiple regression analysis demonstrated that independent contributions in explaining the rate of fetal loss were provided by history of vaginal bleeding and overweight/obese which independently increased fetal loss by 123.075 and 10.035 folds respectively. Conclusion: Difference between mGSD and CRL is correlated with first trimester pregnancy loss in low risk pregnancy and can be used as a marker for it.