Ultrasound for dating pregnancy
Ultrasound has become so helpful that obstetricians now refer to the time before it was used routinely as “the olden days.” We use it to diagnose twins early on; we use it to document appropriate growth as the pregnancy progresses; we use it to determine fetal health; and we use it to guide conversion of breech to vertex (head-first) position and to guide amniocentesis.
Of all of these uses, dating the pregnancy is the most common reason to use ultrasound, particularly when the expectant mother cannot remember the date of her last period (as in breast-feeding or irregular cycles).
However, if you have a larger than average baby, the ultrasound will apply the husky figures to the “normal” measurements.
This creates error in that the baby will compute out to be further along than he or she really is.
Measurement of the fetal pole from one end to the other is called thecrown-rump length (CRL).
This measurement relates to the actual gestational age within five to seven days.
Typically, if the due date suggested by the CRL falls within about five days of menstrual dating, the due date established by the LMP is kept throughout pregnancy.
The absence of cardiac activity may also indicate that the fetus is not developing and may not survive.
The most common site of an ectopic pregnancy is the fallopian tube.
This is a potentially life-threatening situation, due to the risk of hemorrhage.
Your prenatal visits will probably be scheduled every month until 32 to 34 weeks.
After that, they will be every two weeks until 36 weeks, and then weekly until delivery.
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When an ultrasound is performed, measurements of the head, abdomen, thigh, and amount of amniotic fluid are done.