Fetal development in the womb was assessed by using ultrasound to measure crown-rump length.

The most accurate measurement for dating is the crown-rump length of the fetus, which can be done between 7 and 13 weeks of gestation.

Normal thickness depends on the crown-rump length (CRL) of the fetus.

The length of the umbilical cord is approximately equal to the crown-rump length of the fetus throughout pregnancy.

The regression formula which describes this acceleration before the embryo reaches 25 mm in crown-rump length or 9.2 LMP weeks is:

After the administration of general anaesthesia, transvaginal ultrasonography was used to confirm gestational age (crown-rump length) and identify the placenta and amniotic membrane.

The gestational age can be assessed by evaluating the mean gestational sac diameter (MGD) before week 6, and the crown-rump length after week 6.