Determine Cutoff BMI at which transabdominal sonography (TAS) is not satisfactory for aneuploidy risk assessment.

Obesity is a common public health problem which is increasing worldwide at an alarming rate. According to National nutrition survey statistics of 2007, the prevalence of obesity in the kingdom of Saudi Arabia was 23.6% in women and 14% in men. Also the prevalence of overweight in the Saudi community was determined to be 30.7% for men as compared to 28.4% for the women.

First trimester screening between 11-14 weeks gestation is known to be an effective and reliable screening test for Down syndrome and trisomy 18.First trimester screening allows earlier identification of the pregnancy at risk for fetal aneuploidy and anatomic defects, particularly, cardiac anomalies, therefore, providing an option of earlier diagnosis by chorionic villus sampling and analysis of amniocytes.

The well-known association of obesity during pregnancy with a variety of maternal and fetal complications increases the importance of early aneuploidy screening.

Fetal aneuploidy risk assessment is based on a combination of maternal age, prior affected pregnancy or family history, maternal serum biochemical tests and fetal ultrasound markers.

The impact of obesity on the quality of prenatal ultrasound examination is well established with a greater risk for suboptimal visualization, in particular, the fetal cardiac structures and the craniospinal structures only when body mass index above the 90th percentile.

The quality of prenatal screening for aneuploidy via nuchal translucency thickness measurement is significantly limited among obese pregnant women, thus, increased risk of fetal anomalies.

Gandhiet al, have noted that increased BMI is not associated with suboptimal visualization of nuchal translucency, but it is associated with a longer time to perform the first-trimester ultrasound examination for aneuploidy risk assessment, increased need for transvaginal ultrasound examination for optimum nuchal translucency visualization.

There is evidence suggesting that fetal anatomic evaluation in the low-risk gravida can be better accomplished in the first trimester using the transvaginal route, providing a valuable option for obese patients.

Inclusion Criteria:

• women who have a live, intrauterine, singleton pregnancy between 11- 14 weeks gestation.

Exclusion Criteria:

• multiple gestation.
• fetal size outside of nuchal translucency screening age (crown-rump length (CRL) outside of 46-71 mm).
• presence of a cystic hygroma.
• fetal demise.

Inclusion criteria will consist of women who have a live, intrauterine, singleton pregnancy between 11- 14 weeks gestation.