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Thread: OB ultrasounds for checking dates?

  1. #1

    Default OB ultrasounds for checking dates?

    AAPC: Back to School
    We have the ongoing situation that a patient will not know their last LMP so the doc ends up doing an ultrasound to evaluate fetal age and confirm fetal viability. We will usually find out they are only 5 to possibly 8 weeks along. SO it is too soon for the first ultrasound. They wlll later in 3-4 weeks do the first ultrasound and then after 14 weeks the fetal anatomy scan.

    Does anyone else have docs that do this? If so, What are you guys putting down for a diagnosis for this "need to check for dates" and "viability" ultrasound?

    Thanks in advance....

    Rhonda Green, CPC

  2. #2


    Thank you for the topic R.Green. I hope I would brief a little about it.
    Here we go:

    Fetal growth and date Detection as early as when? :
    It is recommended that all pregnant women have a scan in the first trimester at around 12 weeks of pregnancy to confirm their dates. First trimester ultrasonic scans may show 'soft' markers for chromosomal abnormalities, such as an increased fetal nuchal translucency (back of the neck) to enable detection of Down's syndrome fetuses.

    There is no hard and fast rule for the number of scans you should have during pregnancy.
    If unsure of her period dates or have an irregular cycle, she is suggested to meet up with her doctor, midwife or health care provider as early as possible to arrange for a dating scan.
    6weeks: The heart begins to beat AT 6 weeks of pregnancy (ie) 4weeks of her gestation (for those whose has 28-30days cycle)
    7weeks: The heart has divided into the right and left chambers and is beating about 150 beats a minute which is about twice the rate of an adult. The heart has divided into the right and left chambers and is beating about 150 beats a minute which is about twice the rate of an adult.
    Weeks 11 Baby movements seen within the bag of fluid
    Weeks 12 From this week you may well be able to hear the baby's heart beat through a doppler monitor on her abdomen.
    What is crown to rump length (CRL) and when is it? :
    The crown rump length is a universally recognized term, very useful for measuring early pregnancies. The CRL (see image above between the two white + marked 1) is highly reproducible and is the single most accurate measure of gestational age. Charts have been developed for this purpose, but some simple rules of thumb can also be effectively used. From 6 to 11 weeks gestational age, the fetal CRL grows at a rate of about 1 mm per day.

    Crown Rump Length:
    Gestational age = 6 weeks plus (CRL x days). For example, a CRL of 23 mm would correspond to a gestational age of 9 weeks and two days (6 weeks plus 23 days = 9 weeks and 2 days). Accuracy of CRL after 12 weeks in predicting gestational age diminishes and is replaced by measurement of the width of the fetal head (biparietal diameter or BPD)
    What is the 12 week NT scan?
    The 12 week scan is a routine ultrasound examination carried out at 10 to 14 weeks of gestation. During the examination, the fetus is seen by abdominal ultrasound. Occasionally the view is not clear and it may be necessary to perform a vaginal scan. At the first trimester scan they confirm that the fetus is alive, they assess the gestational age by measuring the crown-rump length and will also look for any major problems.
    What is the Nuchal Translucency?
    The nuchal translucency is a collection of fluid beneath the fetal skin in the region of the fetal neck and this is present and seem in all fetuses in early pregnancy. The fluid collection is however increased in many fetuses with Down's syndrome and many other chromosomal abnormalities. It is called a 'translucency' because on ultrasound this appears as a black space beneath the fetal skin. It is this black space that you will see measured during the ultrasound scan.

    Currently the most accurate non invasive test for detecting Down syndrome during pregnancy is the measurement of the nuchal translucency with an ultrasound between 11 to 14 weeks of pregnancy. This is normally less than 2.5mm and when seen increased (greater than 2.5mm, see image on the right) may indicate the baby has Down syndrome or may indicate another chromosomal abnormality. 95% of measurements will indicate a reduced risk.

    Now, when you refer to the CPT, 76801 US at less than 14weeks 0days, trans abdominal, single or first gestation. 76813, for first Trimester fetal nuchal translucency measurement.
    Thank you for your patience!

  3. #3
    Join Date
    Apr 2007

    Default Unknown lmp dx for u/s


  4. #4


    R Green has already given the diagnosis code : 649.63 -Uterine size date discrepancy.
    This is more appropropriate diagnosis code .ANy othercode cannot come closer to that.

    Your diag. code 626. 4 is not for current pregnancy /status. It is a Gyn condition "Irregular Menstual cycle" -Irregular bleeding NOS, menstruation, period etc. All these do not denote UNKNOWN LMP. totally deferent senerio connected with menstrual disorders. It does not mean that the patient is 'unaware of her LMP/ unknown LMP'
    Anyway, thank you for your info

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