Obstetrical Ultrasound Seattle First Trimester
Early First Trimester less than 14 wks. In the first trimester exams are completed to demonstrate the viability of the pregnancy. The heartbeat can be detected at about 6 week menstrual age. This is also the most accurate time to date the pregnancy.
Other indications for a first trimester screening include bleeding problems or risk for a miscarriage. The baby can be measured in its entire length up to 13-14 weeks pregnant. A crown rump length is a measurement that gives your physician the gestational age of the baby by measuring the top of the baby’s head to the rump of the baby. The limbs (arms or legs) are not included in this measurement. Some of the things the sonographer will be looking for is fetal movement, fetal heart tones, the fluid around the baby, placenta formation,diagnosing a multiple pregnancy,ruling out an ectopic pregnancy.
If you are about 10 weeks pregnant or less your Ultrasound exam will typically require an trans-vaginal approach in addition to the full bladder technique. In order to have a trans-vaginal ultrasound, you will be asked to empty your bladder.
If you are between 11-14 wks pregnant we can usually use a trans-abdominal(external) approach, but sometimes a trans-vaginal scan is necessary if the uterus is tilted.
Other indications for a first trimester screening include bleeding problems or risk for a miscarriage. The baby can be measured in its entire length up to 13-14 weeks pregnant. A crown rump length is a measurement that gives your physician the gestational age of the baby by measuring the top of the baby’s head to the rump of the baby. The limbs (arms or legs) are not included in this measurement. Some of the things the sonographer will be looking for is fetal movement, fetal heart tones, the fluid around the baby, placenta formation,diagnosing a multiple pregnancy,ruling out an ectopic pregnancy.
If you are about 10 weeks pregnant or less your Ultrasound exam will typically require an trans-vaginal approach in addition to the full bladder technique. In order to have a trans-vaginal ultrasound, you will be asked to empty your bladder.
If you are between 11-14 wks pregnant we can usually use a trans-abdominal(external) approach, but sometimes a trans-vaginal scan is necessary if the uterus is tilted.
First Trimester Screening For Downs Syndrome
The vast majority of babies are healthy, but about 1 in 100 are born with a serious mental or physical handicap. One of the commonest conditions is Down syndrome, when the baby receives an extra chromosome 21 (Trisomy 21). It is more common with older mothers, but can occur whatever the age of the mother (see the table below).
The vast majority of babies are healthy, but about 1 in 100 are born with a serious mental or physical handicap. One of the commonest conditions is Down syndrome, when the baby receives an extra chromosome 21 (Trisomy 21). It is more common with older mothers, but can occur whatever the age of the mother (see the table below).
Chance of Down syndrome
Maternal age *yrs* At 12 Weeks At Birth
20 1 in 1070 1 in 1530
25 1 in 950 1 in 1350
30 1 in 630 1 in 900
32 1 in 460 1 in 660
34 1 in 310 1 in 450
35 1 in 250 1 in 360
36 1 in 200 1 in 200
38 1 in 120 1 in 170
40 1 in 70 1 in 100
42 1 in 40 1 in 55
44 1 in 20 1 in 30
Maternal age *yrs* At 12 Weeks At Birth
20 1 in 1070 1 in 1530
25 1 in 950 1 in 1350
30 1 in 630 1 in 900
32 1 in 460 1 in 660
34 1 in 310 1 in 450
35 1 in 250 1 in 360
36 1 in 200 1 in 200
38 1 in 120 1 in 170
40 1 in 70 1 in 100
42 1 in 40 1 in 55
44 1 in 20 1 in 30
Screening for Down's Syndrome
The only way to be certain whether the fetus has Down syndrome or not is by doing a diagnostic test called amniocentesis or chorionic villus sampling (CVS). A CVS is performed between 11 and 13+6 weeks and involves taking a small amount of tissue from the placenta; an amniocentesis involves taking fluid from around the baby and is usually done after 15 weeks. Both provide a sample that contains tissue that has the same genetic make-up as the baby and will allow the baby's chromosomes to be looked at in detail. But the problem with these invasive tests is that they can cause a miscarriage, even if the baby is entirely normal. The risk of miscarriage is about 1%.
Therefore the decision as to whether to have an invasive test or not must be taken on the basis of a non-invasive assessment of the likelihood (risk) that the baby has Downs syndrome. The most accurate way of estimating this risk is by combining the information from:
The nuchal scan is performed between 11 and 13+6 weeks of pregnancy, during which the fluid at the back of the baby's neck (the nuchal translucency) is measured. All babies will have some fluid there, but in babies with Down syndrome the fluid tends to be increased.
The other things we can do during this scan include: Confirmation of your dates;Check that the baby is developing normally; confirm a single or multiple pregnancy;evaluate the fetal anatomy that is visible at this gestational stage.
Therefore the decision as to whether to have an invasive test or not must be taken on the basis of a non-invasive assessment of the likelihood (risk) that the baby has Downs syndrome. The most accurate way of estimating this risk is by combining the information from:
- The age of the mother
- The findings from an ultrasound scan at 11-13+6 weeks (the nuchal translucency scan)
- Information obtained from the levels of certain pregnancy hormones in the mother's blood
The nuchal scan is performed between 11 and 13+6 weeks of pregnancy, during which the fluid at the back of the baby's neck (the nuchal translucency) is measured. All babies will have some fluid there, but in babies with Down syndrome the fluid tends to be increased.
The other things we can do during this scan include: Confirmation of your dates;Check that the baby is developing normally; confirm a single or multiple pregnancy;evaluate the fetal anatomy that is visible at this gestational stage.
