Gestation by LMP is calculated from the first day of the last menstrual period. Gestation by CRL is calculated: Weeks = 5.2876 + (0.1584 * Crown_Rump_Length) - (0.0007 * Crown_Rump_Length2). This will be gestation at time of ultrasound.

How accurate is CRL measurement?

Up to and including 13 6/7 weeks of gestation, gestational age assessment based on measurement of the crown–rump length (CRL) has an accuracy of ±5–7 days 11 12 13 14. Measurements of the CRL are more accurate the earlier in the first trimester that ultrasonography is performed 11 15 16 17 18.

What is the normal range of CRL?

The mean and median values of CRL were (59.6 ± 9.2) mm and 58.3 mm, respectively. The mean and median values of NT thickness were (1.7 ± 0.5) mm and 1.7 mm, respectively.

What is the normal CRL at 7 weeks?

Table 4CRL (mm)GA (wks, days)GA (days)7.0 mm6W6D47.87.5 mm6W6D48.28.0 mm7W0D48.68.5 mm7W0D49.150 more rows

Is NT 1.5 normal?

The normal range of NT for this age is 1.5-3 mm. Although she refused to do the triple test and fetal echocardiography, follow-up prenatal ultrasound findings and amniocentesis (karyotype) were normal.

What if CRL is less than expected?

Conclusions. There appears to be an association between a smaller than expected early CRL and a higher likelihood of first trimester miscarriage in singleton pregnancies conceived by IVF/ICSI. This data can be useful in clinical practice to assist in the decision of a re-evaluation by early scan.

What if NT scan is not normal?

What if your NT results are abnormal? If your nuchal translucency screening or any other prenatal screening results indicate that your baby may be at an increased risk of having a genetic abnormality, your practitioner will likely suggest a diagnostic test like chorionic villus sampling (CVS) or amniocentesis.