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Placenta Previa/Placenta Location

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General



NOTE - If you have an ultrasound scan after 20 weeks to see if the placenta has moved up, it's helpful to be aware that if you are anxious and fearful, the increased adrenaline may cause a uterine contraction.  This contracts or shortens the space between the placenta and the cervix, so the measurement they get will be inaccurate.  The technician may notice that sometimes the placenta seems closer and other times it seems farther away from the cervix.  This probably means you're having contractions.  If you get to the last ultrasound before planning a cesarean, it might be helpful to take some extra magnesium, which is a harmless muscle relaxant when taken in reasonable doses.  The RDA for magnesium in pregnancy is 360 mg, which many people would say is too low.  Many people recommend that calcium and magnesium should be balanced in a 1:1 ratio, since calcium is needed for muscle contraction, and magnesium is needed for muscle relaxation.  (The current 2:1 ratio is an artifact of the ratio in oyster shell calcium, one of the first and least expensive sources of calcium supplements.)  Or, if you prefer the medical approach, you could ask to receive a medicine that will relax the uterus.



Club Previa - This is a very upbeat site put together by a mom, Karen Cork, who had placenta previa.


A low-lying placenta after 20 weeks (placenta praevia) - patient information from the Royal College of Obstetricians

Placenta Praevia and Placenta Praevia Accreta: Diagnosis and Management (Green-top 27) - Clinical Green-top guideline from the Royal College of Obstetricians



Placenta Previa on Early Ultrasound Reports



Placenta previa - 97% of early diagnoses are misdiagnosed.

Ultrasound screening and perinatal mortality: controlled trial of systematic one-stage screening in pregnancy. The Helsinki Ultrasound Trial.
Saari-Kemppainen A, Karjalainen O, Ylostalo P, Heinonen OP
Lancet 1990 Aug 18;336(8712):387-91
The Saari Kempaainen study revealed that 150 women were diagnosed as having placenta praevia; when they got to term only 4 women actually had it. In the control arm the women who were not exposed to ultrasound also had 4 women whose placenta praevias were discovered when they went into labour. Both sets of women had caesarean sections and there was no difference in outcomes. The researchers did not investigate the amount of stress a diagnosis of placenta praevia could have caused in the 146 misdiagnosed women. This research shows that early diagnosis of placenta praevia is irrelevant and a complete waste of time, yet doctors and midwives persist in telling women they have low lying placentas.

The relevance of placental location at 20-23 gestational weeks for prediction of placenta previa at delivery: evaluation of 8650 cases.
Becker RH, Vonk R, Mende BC, Ragosch V, Entezami M
Ultrasound Obstet Gynecol 2001 Jun;17(6):496-501

"CONCLUSION: At 20-23 weeks, a combination of routine transabdominal and indication-based transvaginal location of placental position is a powerful tool in predicting placenta previa at delivery. The advantage of determining placental position at this stage of pregnancy is a low false-positive rate compared to at earlier stages of pregnancy. We conclude that an overlapping placenta at 20-23 weeks has the consequence of a high probability of placenta previa at delivery. An overlap of 25 mm or more at 20-23 weeks seems to be incompatible with later vaginal delivery. "

See also Related Articles


Low lying placenta from Danny Tucker's pages


[from ob-gyn-l]


My pet peeve are the ultrasound reports. Why do the sonographers insist on reporting 'marginal previas' at 15 week ultrasounds? I have even ordered ultrasounds later in pregnancy for other reasons and the report will say that the previa "resolved". I had an old but well-respected OB tell me when I was a student that the placenta actually had 'fingers' and it could 'crawl up the uterine wall' to its appropriate place.


They report it that way for medical-legal reasons. The guidelines say that in the 2nd trimester one must comment on the location of the placenta. If one does not and there is a previa later, they are guilty of violating the standard of care for an ultrasound.


I keep trying to teach the residents that placentas do not move, they are attached to the uterus. If it "resolves" at 37 weeks or at 15 weeks or at any other time, then it never really was. It only looked like it was. The problem is that until the head gets down into the lower part of the uterus, the placenta which is a big bag of blood(fluid) can just sort of ooze down there around the cervix and look like a PP. In case you hadn't noticed, this is one of my soapboxes. It gets me to respond every time. The residents say "Oh no, here he comes again."


I take issue with the statements "teach residents that placentas do not move, they are attached to the uterus.". and "resolves at 37 weeks or at 15 weeks or at any other time, then it never really was. It only looked like it was." (See below).

Yes, the placenta is attached, but I have seen serial studies in which the positions were quite different,.... they changed. As have many other folks, that is why the phrase "Placenta Migration" came into being after sonography was developed. But the placenta is not crawling with fingers. Dr. Harris Fineberg elegantly explained this phenomenon, as trophotropism. The tendency to grow toward better nutrition and away from poorer nutritional states. Look it up in a medical dictionary. Or see the discussion in the OBGYN.net Forums below (we've been through this before, search for placenta+previa). Or better yet, buy my book, DuBose TJ, FETAL SONOGRAPHY, W. B. Saunders Co. 1996 and read pages 358-362. ;-)


I agree that the main reason for the constant comment is medical-legal. Also, if the placenta has a portion, which is slightly across the internal os demonstrated by sonography, then that is how it must be called at that time. Even though we all realize that later it will probably be higher up.

One last thing. The report (Dx) is usually issued by a Sonologist (M.D.). The sonogram is often done by, and a Sonographer's Impression (but that isn't a Dx) may be given by a Sonographer, RDMS, to an M.D. who does issue the Dx. This medical-legal stuff does drive me crazy too, but it is real, and we must deal with it as long as the lawyers are about.



Locating Placenta Using a Hand-held Doppler



You heard the placenta? Please explain. What, exactly, in the placenta makes a distinct noise you can hear with a Doppler?


I always go "placenta hunting" with my Doppler at around 35 weeks. The placenta makes a very different sound than the heart or even the cord. There is a very distinct "swoosh" sound with the placenta. If I cannot find the placenta at all, I usually assume that it is just too posterior to locate via Doppler. One good way to practice getting the sound difference down, is by simply placing your Doppler at the top of the fundus on all of your mommies at around 35 weeks. Since so many placentas are at the top of the fundus, you will have a chance to experience that sound, then when it is low lying, or in some other strange place, you will know that sound. :-)


It is also easy to hear with the fetoscope. Sometimes when the HT are not loud enough for the mom to hear she can still hear the placenta with the fetoscope.


I just can't see how the Doppler, which is only responding to blood flow velocity, can sound different if the blood vessels it's "seeing" happen to be in a placenta.

Have you verified this by marking where you "hear" the placenta, then having ultrasound done to confirm it? Has anybody done such a study? If this phenomenon is true, it should be easy to demonstrate it.


I don't know if any studies have ever been done on this, and I have never sent a woman for ultrasound for the sole purpose of confirming that the placenta is where I think it is. But on that rare occasion when I have had to send a woman for an ultrasound, I always double check (usually I go with the mom for her US) the location of the placenta. It helps me to determine if I am accurate most of the time. Which... I am usually pretty accurate. Has anyone else also had this experience?


I have done this many times. I don't routinely placenta hunt, but have often suspected an anterior placenta. I'm sure many of us have had the experience, the mum is complaining of lack of fetal movements even at 20 weeks, even if multip, and placental sounds are heard anteriorly, making getting a FH difficult, even with a dop. You often have to listen for FH very low or from fundus down. In the last couple of years, I or the midwife I was working with had occasion to have u/s done on some of these women, for other reasons, and we always marked the reports, that we had predicted the anterior placenta. I don't think we had any that we thought were anterior that were not.


I was taught this too, and have always noted it on my charts just in case we needed a u/s during the pregnancy. On occasion a subsequent u/s agreed with this; but not often!

I chart it as "Loud vessels heard upper right quadrant etc." and I think that's what they are.

We can't tell by looking at the placenta after birth whether our guess about location was right (Unless the membranes are in good shape and then we can only confirm whether the placenta was high or low, but NOT posterior, right, anterior, left etc.).


I've had my Doppler assessments of placental location verified by U.S. One thing I look for in addition to the placental souffle is a cord insertion. I make a note in pencil on my chart so when I get the US report I can verify my assessment then erase!. It's one of those things you want to be able to erase, as the medical community thinks you're nuts to think you can locate the placenta w/o us.

When I got one of my Medisonics Dopplers, from Cascade, it came with a bunch of printed info on use of the Doppler. It had a study included on locating the placenta with the dop., and instructions. I found it to be of mild interest, so I didn't exactly memorize it. But I do remember that it gave specific instructions for locating a posterior placenta with the dop. Posteriors are harder to pin down.


I use an Allen fetoscope and have heard the difference between heart and placenta, when listening it covers a larger area than when hearing a cord or the baby's heart as well as swooshing differently ; )


Low lying placentas can present some difficulty because of femoral pulsing. I also find these are the heart tones most difficult to hear with a fetoscope. We determine the approximate location of implantation after the birth. If the hole in the membranes is close to the edge of the placenta, that confirms it :-)


Yep -- I always look for the hole to confirm my suspicions -- It was very interesting to see after the people last summer who supposedly had the vasa previa. (Long story, if you have subscribed recently) That was not the case, but U/S also showed very low lying placenta. Hole was right ON placental lobe. I have seen that a few other times, but of course, we didn't know to worry until after the fact! I've been listening to placentas since I was an apprentice -- one of the first things I was taught. I believe it's easier to hear a placenta with fetoscope, but is possible with Doppler -- I've heard cord right above pubic bone, several times, too, with dop -- meaning probable cord around the neck. (I even palpated that once) I use Doppler to confirm position, all the time. Can figure out OP and OA, etc., by finding the actual heart. I love using the Doppler in those ways, and it makes me feel less guilty about using the Doppler instead of the fetoscope!


You Betchya! You can hear a difference between cord, placenta and fetal heart. Do a simple demonstration project with your office Doppler and then confirm with your ultrasound machine...better yet have the u/s report in hand UNREAD and then listen and see if you can hear the difference. If you get good at Dopplers (Dopplers are for wimps) get out your fetoscope and see if you can distinguish placental souffle (spelling?).

Here is your chance to publish a very straight forward study that may decrease the "need" for ultrasounds and save insurance companies big bucks.


Here's something else you can hear w/ a Doppler...fetal breathing movements. Taught to me by an OB (high-risk fetal-maternal medicine type) that I did a placement with. Hard to describe, but very distinctive, once you've heard it. Reassuring during those last weeks of pregnancy, as that's one of the signs of fetal well-being.


oh, PLEASE try to describe it! -- that would be an excellent skill to learn, reassuring for those questionable babies -- especially for my moms who won't get U/S.


Well, here goes. It sounds like a subtle, rhythmic "whoosh", very soft, and much softer than the placental or uterine souffle, also usually much slower, as well. The sound is caused by an increase in vascular resistance with the breathing movement, or so I was told. If you're lucky, with a skinny mom, you can also see it at the same time. This is not the same as hiccups, which usually sound quite loud w/ the Doppler, and the movement much more jerky and distinct.

I've noticed it a number of times since I was taught about it. The only problem w/ using it intentionally is around the periodicity of fetal activity which occurs in about 90 min cycles. You could wait a long time at a sitting before you heard it.


[from ob-gyn-l]


Blood flow through the intervillous space has a sound like wind blowing through the trees. (Frequently Aspens) However so does blood flowing through veins. This could possibly lead to a correct diagnosis of a general placental location in some cases, but I doubt that it would work with consistent enough accuracy to replace ultrasound. I know of no studies. The above reflects expert (I hope) opinion based on a few facts and a lot of experience.



How Placentas "Migrate" in Pregnancy



Difference in migration of placenta according to the location and type of placenta previa.
Cho JY, Lee YH, Moon MH, Lee JH.
J Clin Ultrasound. 2008 Feb;36(2):79-84.

RESULTS: The incidence of migration in the group of anterior placentas was significantly higher than that in the group of posterior placentas. The mean migration rate in the anterior group was 2.6 mm/week, whereas that in the posterior group was 1.6 mm/week. The migration rate of incomplete PP was significantly higher than that of LLP. Incidence of cesarean section for nonmigrated PP was significantly higher in the posterior group. The incidences of premature delivery and vaginal spotting were also significantly higher in the posterior group.
CONCLUSION: Anterior PP and LLP may migrate more often and faster than posterior PP. Our results may be useful for planning of prenatal management and counseling patients with PP and LLP.


[from ob-gyn-l] I see the apparent migration as simply growth of the uterus. no change in implantation site, simply more area between the cervical margin and the placental edge. the decrease in previas seen on u/s at term being due to a decrease in the proportion of uterine wall occupied by placenta at term compared to the proportion at 16-20 weeks . and no i have no good evidence for this.



Anterior Placenta



See also: Posterior Position


Often, an anterior placenta takes up some room in the front of the mom's belly that would otherwise be occupied by the baby's back.  This can sometimes cause the baby to be somewhat posterior, although this tends to correct itself as the baby moves lower into the pelvis and the back moves down, beyond the placental location.

Sometimes, in an effort to correct this apparent posterior position, moms will spend a lot of time on hands and knees.  This can be a problem with an anterior placenta in that then the baby's weight is right on top of the placenta, which can cause some cord compression, especially with big babies or low fluid levels.  This can result in minor fetal distress or meconium.

So moms with anterior placentas who are doing hands and knees might want to limit the time to 2 or 3 minutes at a stretch.


Can anyone help provide information about the implications of an anterior placenta? I've searched my medical texts and the Web and found nothing other than the implications regarding placement of the needle for amniocentesis.

Are there any implications for fetal growth or labor and delivery?

I can imagine that an anterior placenta might predispose a baby to a posterior presentation, and possibly even to a breech presentation.

If the blood vessels are less dense in the anterior uterus, perhaps there could be implications for mild IUGR. But then one might expect reduced risk of postpartum hemorrhage.

I'm labor coaching for a client whose OB mentioned it with one of those "Well, this bumps you up into a higher level of risk" tone of voice, and she was worried.


No problems, other than sometimes posterior,( baby curls around placenta), or harder to hear FHTs because of loud souffle.


I'm kind of wondering why you're worried about it...I figure that lots of women have anterior placentas. There has been a suggestion that they may somewhat predispose to posterior presentations, but the only thing that I find is that women (particularly multigravid) may feel less fetal movement with them. I figure that this is because there is more "insulation" between the fetus and the outside world, as it were. In one instance not too long ago, I was sure the placenta was anterior, but the mother was worried about fetal movement. Sent her for U/S and guess what? I was right. Only thing I noticed was that the baby consistently laid on the opposite side of the uterus to the placenta. Everything else was completely normal.


Wouldn't the only risk be during the ( waaaay outside) chance that she would need a c-sec? Because if the placenta is anterior making the incision would be dicey-they would have to deliver the placenta and the babe at the same time, and blood loss could be a concern.

I had a low lying anterior placenta with my 2nd pregnancy, and the only challenge was hearing my son! Sometimes it took a good 10-15 mins. to get clear heart tones. Maybe this is what the doc is concerned about? It would seem that using a doptone would make that easier (my mw used a fetoscope). Other than that everything.


I don't know of anything significant with anterior placenta placement. It just may make the FHR harder to pick up depending on the baby / placental positions. The only other problem would be that if a cesarean section was needed the OR team would have to be careful (and would hopefully be able to determine placental placement prior to the incision).


Can be harder to palpate, to get clear FHT; mom may perceive less movement.


There is some evidence that women with anterior placentas feel quickening later and also experience less fetal movement. I don't know how much research has been done on it but it does make some logical sense.


I've definitely found this to be true in my practice. Moms need lots of reassurance about late perception of fetal movement. I tell them that the placenta acts as a pillow between the moving baby and their abdominal muscles, which sense the baby's movement. The baby is still active, but the movement is "muffled" by the placenta.


The main thing is that if the mother has ever had a C-section or anything that could scar the anterior endometrial area then she is at higher risk for placenta accreta.


Having an anterior placenta can interfere with an external version to turn a breech baby at term, so if you have an anterior placenta, you might want to doublecheck with your provider to make sure the baby is head down by 34 weeks and request an external version then, while the baby is small, rather than waiting until 38 weeks, the typical time.



VBAC Issues with an Anterior Placenta



Because the Cesarean scar is in the front of the uterus, i.e. the anterior, an anterior placenta may be implanted directly over the uterine scar.  Sometimes this causes the placenta to grow into or through the uterine wall so that it does not detach properly after the birth.  This can be a life threatening situation and is well outside the scope of midwifery.


Surgery in the presence of Placenta accreta, increta and percreta [see item 6] from the Royal College of Obstetricians and Gynaecologists:

"Women who have had a caesarean section in a previous pregnancy and who have a placenta praevia subsequently should be considered at high risk of having a morbidly adherent placenta. In such cases particular attention should be focused to confirming or excluding this diagnosis using ultrasound imaging. When present, senior anaesthetic and obstetric input are vital in planning the delivery."

"The association between placenta praevia and placenta accreta is strong, with a relative risk of 2,065 compared to women with a normally sited placenta.30 This is also associated with scarring of the lower segment of the uterus, and the risk of placenta accreta in the presence of placenta praevia rises relative to the number of previous uterine incisions.30-32 Ultrasound imaging,33 colour doppler and power amplitude ultrasonic angiography34 and magnetic resonance imaging35 have all been shown to be valuable in the diagnosis of placenta accreta, increta and percreta."

Diagnosis of placenta praevia and accreta after previous caesarean


You can search for placenta percreta at PubMed.  There are some hints that ultrasound or MRI might be able to diagnose or rule out placental problems with a placenta that is located over the uterine scar.

MRI appearance of placenta percreta and placenta accreta.
Maldjian C, Adam R, Pelosi M, Pelosi M 3rd, Rudelli RD, Maldjian J.
Magn Reson Imaging 1999 Sep;17(7):965-71

"MRI is useful for identifying the presence and extent of placenta accreta/percreta."



Vaginal Birth with Placenta Previa



I came across the following in "The Accoucheur's Emergency Manual" by Yingling, first published in 1921 in India, at a time and place where cesareans were not readily available.  I think most of us agree that a cesarean section is the preferred approach with placenta previa, but I also think it's important to have this tucked away in the back of your mind, just in case:

In placenta praevia I fully recommend the method or plan of Dr. H. N. Guernsey, which is "in puncturing the membranes through the placenta and evacuating the liquor amnii."  "The finger must explore a sulcus between the cotyledons of the placenta, and with the same hand a female catheter, previously concealed in the palm, must be forced through the placenta and the membranes during  a pain." "The liquor amnii must be drawn off slowly: and as surely as it thus flows, so surely will the haemorrhage cease.  After the waters have pretty much escaped, the finger may take the place of the catheter, and aid in tearing the orifice larger, so that the presenting parts may descent."  This method applies whether the placenta is central or only partially over the os uteri.

I like to save up these tricks and hope and pray we will never be in a situation to need them. Re -- old treatment for previa -- rupturing membranes was always the first trick -- it often allowed the presenting part to settle down and put some pressure on the bleeding areas, and might make labor proceed more rapidly. Tearing through he placenta might make the birth go faster too -- but in those cases the life of the baby was pretty much forfeit. They were just trying to get the kid out before the mom bled to death.

Thank goodness we live in a time and location where surgery is available for previas and other problems.


Actually, a midwife friend told me of assisting at a birth in a very rural area where there was an undiagnosed placenta previa.  The mom was a multip and the birth was proceeding very quickly.  They tore an opening in the placenta, and it must have moved around the baby's as the cervix dilated, and baby was born just fine.  I'd hate to think of the stress level for everyone involved, but this kind of approach doesn't automatically mean that the baby would die.

 




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