First, the wind up:

Doppler ultrasound is a common tool used to to evaluate blood flow to
the placenta and fetus. This allows for determination of blood flow
problems, such as thromobosis or other clotting/placental problems in
singleton pregnancies, and can be used to determine blood flow as
follows, for example: the blood flow on the screen looks like a
doppler radar or something similar, with different markers for blood
moving in and blood moving out.

For women with Thrombophilia, either Inherited or Acquired, blood flow
needs to be monitored to ensure continued flow to the fetus and watch
for problems. This also allows preventative medication to be
prescribed before the fetus has reached a point where nothing can be
done to save it.

Blood flow through the placenta represents 40% of the fetal cardiac
output. Usually severe problems aren't detected until over 50% of the
blood vessles are lost (source:
http://www.obgyntoday.org/Status%20of%20doppler%20in%20obstetrics.htm)

My question is this:

What are considered the guidelines for appropriate blood flow, week by
week, during the development of a pregnancy? Is there a specific
volume 'guideline' that should be hit, for example, a doppler
ultrasound at X weeks should have Y bloodflow in and Z blood flow out?
If so, I'm looking for a week by week breakdown of what an acceptable
flow for a singleton pregnancy. If there are no specific numeric
guidelines, but only SDRatios (The relationship between blood flow
velocities during systole and diastole) broken by week, month, or
trimester available, I would take that answer.

Thanks.

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Clarification of Question by mynn-ga on 31 Dec 2002 11:28 PST

Further reasearch has led me to find this chart:

http://www.ob-ultrasound.net/xdopwave.html

Which gives the systolic/distolic ratio for weeks 24 through 40 (weeks
22 through 38 fetally).

However, I'm looking for more information on the amounts, ratios,
measurements for earlier pregnancy, say from 8 weeks (6 weeks fetally)
on.

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Request for Question Clarification by tar_heel_v-ga on 31 Dec 2002 12:00 PST

mynn,

I have a formula that was published in the Journal of American
Medicine that that provides the upper and lower S/D ratio for the
umbilical artery in pregancies with normal outcomes as well as some
additional information on S/D ratios during pregancy.  Would this
suffice as an answer?

-THV

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Clarification of Question by mynn-ga on 31 Dec 2002 12:11 PST

> I have a formula that was published in the Journal of American
> Medicine that that provides the upper and lower S/D ratio for the
> umbilical artery in pregancies with normal outcomes as well as some
> additional information on S/D ratios during pregancy.  Would this
> suffice as an answer?

While I have the several formulas, including:

S/D ratio (systolic/diastolic ratio)

resistance index (RI = systolic velocity - diastolic velocity/systolic
velocity)

pulsatility index (systolic velocity - diastolic velocity/mean
velocity)

I'm looking more for the information similar to what was provided in
my original clarification link:
http://www.ob-ultrasound.net/xdopwave.html but for earlier in
pregnancy.

The reason for all these so specific questions is simple: My physician
says they can't really tell anything until the fetus is 16 weeks (14
weeks fetally) by using a level II ultrasound ... I'd like to be able
to convince her to set us up for a doppler examination sooner to
determine if the current rates of flow for the current age are
appropriate to take preventative measures sooner; the blood tests to
determine if IUGR (Intra-Uterine Growth Retardation) is a problem at
this point are very inconclusive. Having watched someon go through
this and get her ultra sound and diagnosis way too late to do
anything, I need information I can hand my doctor and say "Here are
the guidelines for this and the next stages of this pregnancy. Can we
get a tech in here to measure me?"

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Request for Question Clarification by tar_heel_v-ga on 31 Dec 2002 12:18 PST

mynn..

I am not referring to those formulas.  These are scientific formulas. 
A partial of one:

An equation approximating the low limit is:

S/D ratio lower limit = ((0.0001413 * ((weeks gestation)^3)) -
(0.011805 *....

I have one for the upper ratio limits of S/D, as well as the upper and
lower limits for pulsatility index.

-THV

---

Clarification of Question by mynn-ga on 31 Dec 2002 12:22 PST

Yes, Tar_heel, sounds like that would cover what I'm looking for splendidly!

mynn,

Thank you for your question.  Prior to providing your answer, I would
like to remind you that answers and comments provided on Google
Answers are general information, and are not intended to substitute
for informed professional medical, advice.  Obviously you are aware
that you should discuss all aspects of your pregnancy with your
physician.

There are formulas you can use to determine the upper and lower S/D
ratios and pulsatility index during your pregnancy:

"Evaluation of Umbilical Artery Doppler Ultrasonography Data

Data on the S/D ratio for the umbilical artery in pregnancies with
normal outcomes (Schulman 1990 page 400) was analyzed in JMP.

• An equation approximating the low limit is:

S/D ratio lower limit = ((0.0001413 * ((weeks gestation)^3)) -
(0.011805 * ((weeks gestation)^2)) + (0.2449985 * (weeks gestation)) +
2.0796722)

• An equation approximating the upper limit is:

S/D ratio upper limit = ((0.0001471 * ((weeks gestation)^3)) -
(0.008642 * ((weeks gestation)^2)) - (0.024583 * (weeks gestation)) +
8.1188817)
 

Data on the pulsatility index for the umbilical artery in pregnancies
with normal outcomes (Reuwer 1984 second reference page 202) was
analyzed in JMP.

pulsatility index

• An equation approximating the low limit is:

pulsatility index lower limit = ((-0.000174 * ((weeks gestation)^3)) +
(0.0187502 * ((weeks gestation)^2)) - (0.688275 * (weeks gestation)) +
9.2148117)

• An equation approximating the upper limit is:

pulsatility index upper limit = ((-0.000054 * ((weeks gestation)^4)) +
(0.0062881 * ((weeks gestation)^3)) - (0.260467 * ((weeks
gestation)^2)) + (4.3952825*(weeks gestation)) - 22.49588)"

The Medical Algorithms Project
Chapter 15 - Obstetrics and Gynecology
Doppler Ultrasound Assessment of Fetal Blood Flow
http://www.medal.org/docs_ch15/doc_ch15.07.html

Again, while I stress you should seek information from a trained
medical professional, I hope this information proves to be helpful to
you and your physician.  Below, I have also provided some additional
references regarding Doppler, fetal blood flow and intrauterine growth
retardation:

Hygeia
Intrauterine Growth Retardation
http://www.hygeia.org/poems8.htm

University of Oulu 
Placental insufficiency and fetal heart: Doppler ultrasonographic and
biochemical markers of fetal cardiac dysfunction
http://herkules.oulu.fi/isbn9514267370/html/

Aukland District Health Board
Newborn Services
Doppler Studies in High Risk Pregnancy
http://www.adhb.govt.nz/newborn/MedicalGuidelines/DopplerStudiesInHighRiskPregnancies.htm

Good luck and best wishes for your pregnancy.  If you need any
additional clarification, please feel free to let me know.

Regards,

-THV

Search Strategy:
fetal Doppler blood flow velocity waveforms early in pregnancy
normal systolic diastolic ratio pregnancy doppler

Thanks. Pouring through the gobbeldy gook and popular information, I
was going nuts trying to find more scientifically-based data/formulas.


An informed patient ...