To examine the clinical utility of 11-13+6 weeks scan for screening for chromosomal abnormalities and to assess the potential value of the same ultrasound examination in the early diagnosis of fetal structural anomalies.
A prospective interventional study at Fetal Medicine Unit, Fernandez Hospital Pvt Ltd, a tertiary care perinatal center, Hyderabad, India, between September 2005 and March 2010.
All pregnant women < 13+6 weeks at booking are offered a routine obstetric scan between 11 and 13+6 weeks. All scans are done by obstetricians who are accredited by Fetal Medicine Foundation. All expectant mothers undergoing 11-13+6 weeks scan were included; all expectant mothers with antenatal booking after 14 weeks were excluded from the study.
Between September 2005 and March 2010, a total of 11,012 scans were done between 11 and 13+6 weeks. Complete follow-up was available for 7,916 cases; 1,460 are ongoing pregnancies and 1,636 expectant mothers were lost to follow-up. The median maternal age in our population is 27 years and 340 (4.30%) mothers had advanced (> 35 years) maternal age. The median NT in our population is 1.58 mm. Increased nuchal translucency (NT > 95th percentile) was found in 362 (4.59%) scans. Miscarriages/abortions and termination of pregnancy were significantly higher in women whose fetus had an increased nuchal translucency thickness. Nuchal translucency thickness was significantly higher in women with advanced maternal age (ANOVA F = 0.002, Fishers exact test p-value for equality of medians = 0.04). Absent fetal nasal bones were present in 20 (5.57%) of women with increased NT compared to five (0.07%) women with normal NT. Among 7,916 women, 367 (4.64%) women were screen positive for chromosomal abnormalities. After counseling, only 40 screen-positive women accepted prenatal diagnostic procedures. Skull/brain abnormalities were found in 25 fetal images, abdominal abnormalities in 17, spinal abnormalities in eight, bladder abnormalities in five and cardiac abnormalities in five fetal images.
The 11-13+6 weeks ultrasound scan is an important diagnostic tool that should be offered to all pregnant women as a routine standard of antenatal care in the first trimester of pregnancy in India. However, as a screening tool, it mandates addition of cost-effective biochemical tests. To make the combined screening cost-effective, this study calls for making a national policy for Down's syndrome screening for India.