Doctor insights on:
Why Repeat First Trimester Ultrasound For Twins
How accurate are 1st trimester ultrasounds in estimating gestational age? What about 2nd trimester ultrasounds?
Accurate!: 1st trimester ultrasounds are very accurate - have correlated with timed ivf pregnancies. We usually consider 1st trimester scans accurate within 5-7days' 2nd trimester scans within 10-14days. ...Read more
An ultraound, also known as a sonogram, is a painless and relatively inexpensive imaging test that utilizes sound waves instead of ionizing radiation. There are no side effects. Ultrasound can give us two-dimensional, and in some applications three-dimensional, images of structures and organs in virtually any part of the body. In addition to diagnostic uses, such as evaluating abnormalities in the abdomen, pelvis, and breast, ultrasounds are commonly used to guide needle and catheter placement in a variety of surgical ...Read more
Very accurate: Ultrasounds tend to get more inaccurate as your pregnancy progresses. First trimester ultrasounds are more accurate than second trimester ultrasounds, which are in turn more accurate than third trimester ultrasounds. First trimester ultrasounds can reliably predict gestational age within 5-7 days. ...Read moreSee 1 more doctor answer
Diagnostics: This question is hard to answer because it depends upon what you're looking for with your first trimester ultrasound. If you're trying to figure out how far along you are in the pregnancy that is excellent, if you're trying to figure out if your baby has down syndrome it's not perfect and will require further work up with other blood tests and ultrasounds. ...Read more
May...: In some places it is a routine to test for the basic STD's again in the third trimester but in general the CDC recommends to repeat testing at that time if there are risk factors that can point to possible active infection.Usually if the pt is younger than 25 y/o,has been recently exposed to STD's,was treated for an STD, or is a high risk for exposure( ex. multiple partners, infected partner, etc) ...Read more
What changes a due date? And why is the first trimester ultrasound more accurate than the second trimester ultrasound?
Ultrasound dating.: First trimester ultrasound is by far the most accurate in determining the precise due date (+/- 3-7 days, depending on exactly when it is performed). Second trimester sonograms are less accurate but still helpful in pegging down the due date within +/-7-12 days. Third trimester scans are not very accurate in dating the pregnancy, as growth varies (+/- 14-21 days). Menstrual dating is not very good. ...Read more
Within 3 days usu.: 6 days maximumGet a more detailed answer ›
Recommended: Most obs perform a high-resolution us between 18-20 weeks to rule out anomalies. It's a good time to screen the fetus, document placental location, and even check gender. We no longer "wait & see" when it comes to labor since there's an advantage to having the right equipment & personnel at delivery if an abnormality is present. ...Read moreSee 1 more doctor answer
How accurate are second and third trimester sonogram measurements in figuring date of conception?
No: A late first trimester ultrasound (i.e., 12 weeks) may be off by as much as a week in either direction but unless done by a completely incompetent sonographer, 3 weeks would be unheard of. Earlier in the first trimester the accuracy is even better with a range of less than a week. ...Read more
Why is it better to wait until 8 week gestation versus seven weeks gestation in order to have an accurate dating ultrasound?
Off?: Depends what you mean by 'off.' the theoretical accuracy of a 1st trimester us is considered to be +/- 2-3 days, so in that sense they are always 'off.' if you mean wrong, as in more than 2-3 days, no one knows this - but with a skilled sonographer and a current us machine, it shouldn't be off by more than a few days very often. ...Read more
It can show discord: A first trimester ultrasound is extremely accurate in determining how far along you are, and when the exact due date is. It is possible for it to show that the pregnancy is 2 weeks 'off' from what the expected due date was. As long as it was done by a qualified sono technician or physician, it's unlike for it to be 2 weeks inaccurate in the first trimester. You may have ovulated earlier (or late. ...Read more
Early Ultrasounds: Actually they are thought to be the most accurate. ...Read more
Threatened Sab: You have a threatened miscarriage. Anyone in early pregnancy with spotting is said they have a threatened miscarriage. It is very common, although not normal. As long as you are not bleeding heavily (soaking a pad in an hour) I would just follow up with your obstetrician. ...Read moreSee 2 more doctor answers
Yes : The ultrasound should be used to calculate gestation age ...Read more
Is it possible for ultrasound in pregnancy to give inaccurate dates? I think if further along by 3 wks, 1st trimester
Not 1st trimester: A professionally done first trimester ultrasound is accurate to +/- around 3 days, so there is no way to 'mistake' dates by 3 weeks. Ultrasound by a non-qualified individual could be off by this amount I suppose, otherwise they are extremely accurate. ...Read more
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