Dating ultrasound 11 weeks

17 Feb

After 13 weeks of gestation, the fetal age may be estimated using the biparietal diameter (the transverse diameter of the head, across the two parietal bones), the head circumference, the length of the femur, the crown-heel length (head to heel), and other fetal parameters.Dating is more accurate when done earlier in the pregnancy; if a later scan gives a different estimate of gestational age, the estimated age is not normally changed but rather it is assumed the fetus is not growing at the expected rate.Gestational age is usually determined by the date of the woman's last menstrual period, and assuming ovulation occurred on day fourteen of the menstrual cycle.Sometimes a woman may be uncertain of the date of her last menstrual period, or there may be reason to suspect ovulation occurred significantly earlier or later than the fourteenth day of her cycle.Research shows that routine obstetric ultrasound before 24 weeks gestational age can significantly reduce the risk of failing to recognize multiple gestations and can improve pregnancy dating to reduce the risk of labor induction for post-dates pregnancy.There is no difference, however, in perinatal death or poor outcomes for babies. The bright white circle center-right is the head, which faces to the left.

A gestational sac can be reliably seen on transvaginal ultrasound by 5 weeks gestational age (approximately 3 weeks after ovulation).

Not useful for dating, the abdominal circumference of the fetus may also be measured.

This gives an estimate of the weight and size of the fetus and is important when doing serial ultrasounds to monitor fetal growth.

Ultrasound scans offer an alternative method of estimating gestational age.

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.