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Optimising the timing for nuchal translucency measurement.
Sheila Mulvey1, Lesleigh Baker, Andrew Edwards
1Centre for Women's Health Research, Department of Obstetrics and Gynaecology, Monash University, Victoria, Australia. sheila.mulvey@med.monash.edu.au
Prenatal Diagnosis
|September 12, 2002
Summary
The optimal time for nuchal translucency screening for Down syndrome is 12 to 13 weeks' gestation when using menstrual dates. This timing balances reducing missed miscarriages and ensuring accurate measurements for fetal Down syndrome risk evaluation.
Area of Science:
- Maternal-fetal medicine
- Prenatal diagnostics
- Genetics
Background:
- Effective Down syndrome screening combines nuchal translucency (NT) and serum biochemistry.
- Determining the optimal gestational age for NT measurement is crucial for accurate fetal Down syndrome risk assessment.
Purpose of the Study:
- To identify the optimal gestational timing for scheduling nuchal translucency (NT) measurements based on menstrual dates for Down syndrome risk evaluation.
- To analyze the impact of gestational age on the success and accuracy of NT scans.
Main Methods:
- A retrospective analysis of 5,835 pregnancies undergoing ultrasound scans between 11 and 14 weeks' gestation.
- Data collected included last menstrual period (LMP) or prior ultrasound for dating, missed miscarriage rates, and NT measurement success based on crown-rump length (CRL).
Main Results:
- For LMP-dated scans, advancing gestation significantly decreased missed miscarriage and the need for rescan due to early gestation (p=0.009 and p<0.0001).
- Conversely, advancing gestation increased the rate of unsuccessful NT measurements due to CRL > 84 mm (p < 0.0001).
- For those with prior ultrasound dating, missed miscarriage was 1.6% and 0.3% were too advanced for NT scan.
Conclusions:
- When relying solely on the last menstrual period for dating, scheduling nuchal translucency measurement between 12 and 13 weeks' gestation is optimal.
- This gestational window balances the risks of missed miscarriage with the technical feasibility of NT measurement for Down syndrome screening.