Crown/rump length and gestational age are closely compared with each other until around the end of the first trimester.
The ideal time for a sonographer to assess the gestational age in the first trimester is between 7-10 weeks of pregnancy.
When an ultrasound is performed, measurements of the head, abdomen, thigh, and amount of amniotic fluid are done.
These measurements are computed automatically in the ultrasound machine’s software.
If you experience any complications between your scheduled visits, call your doctor immediately.
(Note: Your caregiver might require you take additional tests. Talk to your caregiver if you have questions or concerns.) Tests in first trimester What to expect Your first ultrasound(s), blood and urine tests When Weeks 11 to 13 (*dating ultrasound is done sooner) Dating ultrasound Not everyone gets this scan but some caregivers offer a dating ultrasound if you’ve had bleeding in the first few weeks or had problems in prior pregnancies (miscarriages, etc.).
First prenatal blood tests After your scan you’ll have blood taken.
The software has certain measurement scales based on data from large populations, and your baby’s measurements are put into this scale.
In other words, by comparing your baby’s measurements to the data from this large collection of measurements, the ultrasound can then tell how far along your baby is.
However, if you have a larger than average baby, the ultrasound will apply the husky figures to the “normal” measurements.