About that placenta…

De formato foetu liber singularis (1626) [1]     

I spent last Monday morning on a doctor’s table with goo on my belly, spying on the womb baby.
We found out the sex and about this baby’s love for doing flips and refusing to sit long enough in profile to get a money shot for the grandmas.

We also found out that I have a low-lying placenta.

“Oh, don’t worry about it”, says the sonographer, “they usually move away from the cervix as the uterus grows.  And if it doesn’t move, you’ll just have a c-section”.

What?  It’s not a big deal, we’ll just cut the baby out?

Sorry, I don’t take that as reassurance.  So, of course, I did a little bit of reading.

First, definitions – A low-lying placenta is defined by the location of its edge being < 2 cm from the opening in the cervix (baby’s escape hatch).  A more serious condition is when the placenta is actually covering this opening; this is called placenta previa.  It comes in two flavors – complete and incomplete.  The terminology specifies the degree of overlap of the cervix with complete placenta previa being the worst case scenario.  A placenta blocking the birth canal can result in hemorrhage and other scary outcomes, which can be avoided by c-section.

So, back to my selfish scenario – what about me?  What are my risks?

Hitting up the always helpful internet for advice, I found that I could decrease my risk of having a low-lying placenta and placenta previa by:   1) not smoking (check);  2) being younger (hmm… can’t do much about this one);  3) not having a previous c-section (check);  and 4) not hitting the crack pipe (big time check).

Not helpful. Plus, it is too late anyway.  The little bugger has already set up shop in this uterus of mine, now it just has to move its blood supply bag out of the way.

The sonographer and my nurse told me that as the uterus grows, the placenta will go with it, moving up and away from the cervix.  Reassuring, yes, but catching a ride on the expanding uterus might not be the true travel mode for the placenta.  Rizos et al. in 1979 note that 90% of placenta previa diagnosed during the 2nd trimester actually migrate to a normal location by term [2].

Wait, migrate?  The placenta can move on its own!?

My research mission:  1) what the hell does placental migration mean?  and 2) What is the likelihood that my anterior low-lying placenta will jump on this train and get out of the way by the time this baby wants out?

Placental migration –  So, we don’t really know how the placenta is doing this magic move technique, but there are are few hypotheses.  The two that rise to the top are the Dynamic Placentation hypothesis and the Trophotropism hypothesis.

Dynamic Placentation is based on the idea that placental attachment points are constantly forming and re-forming [3]. The rearrangement is in response to uterine growth as well as placental growth such that as the lower uterine wall forms and the muscles stretch, the stress causes the attachments in this area to degrade.  As those attachments degrade, new attachment points are formed higher in the uterus in areas that are not subjected to this same kind of growth stress. The placenta creeps along through growth, degradation and re-formation.

Trophotropism – ok, brace yourself, this one is pretty cool (if you are a huge nerd like me).  Picture the placenta as a plant seeking sunlight – plants need sun, placentas need a maternal blood supply.  Phototropism is when plants bend to bask in the best sun beam. Trophotropism is when the placenta migrates to find the best blood supply [4].  A growing uterus means that the bottom portion of the uterine wall gets stretched and, as a result, the blood supply thins.  The placenta then seeks greener pastures, moving away from this thin blood supply and towards the thicker upper uterine wall.  And here we have the same effect – over time, the placenta moves up and away from the cervix.

A different research group suggested that the trophotropism hypothesis would explain why centrally located placenta previa (sitting smack on the cervix) often do not end up migrating during the pregnancy [5].  The cervix has a healthy blood supply – why move?

So what is the prognosis for my anterior (in the front) low-lying placenta?
A study by Cho and colleagues found that, for the studied cases of anterior low-lying placenta and incomplete placenta previa, nearly all cases showed placental migration away from the cervix (28 out of 29) [5].  And the one anterior low-lying placenta that didn’t budge, did not require a c-section at term. The migration, however, was not as strong in those placentas located posterior (in the back).  Migration was noted for 1 out of 7 posterior complete placenta previa cases, 15 out of 22 for incomplete placenta previa, and 36 out of 40 for posterior low-lying placentas.  These data suggest that there is a pretty good chance that my front-sitting placenta is already on the move.


But more importantly, who would win in a placenta race?  Anterior incomplete placenta previa takes that medal with the swift speed of 4.1mm/week. For comparison, the slow pokes include anterior low-lying placenta at 2.2 mm/week and posterior low-lying placenta at 1.4 mm/week.

While I am planning to save the deeper wonders of the placenta for a later post, I wanted to throw in one more tidbit – how the hell does the little ball of cells know where to implant itself?

There are many studies addressing this (and I hope to include them in that later post) but one simple study suggests that we might have good ‘ol gravity to blame [6].  The authors found that women who preferred to sleep on their right side, were more likely to show right-sided placentas.  The opposite held true for the left-sided sleepers.  The authors, publishing their findings in Military Medicine, were very concerned about zero gravity insemination.

Add this one to the list of things to decrease the risk of a misplaced placenta – 5) don’t get pregnant in space.



1De formato foetu liber singularis (1626)

2Rizos N, Doran TA, Miskin M, et al. (1979) “Natural history of placenta previa ascertained by diagnostic ultrasound.“ Am J Obstet Gynecol. 133: 287.

3King DL. (1973). “Placental migration demonstrated by ultrasonography.” Radiology 109:167. 19.

4Benirschke K, Kaufmann P. (1990) The pathology of the human placenta. New York: Springer-Verlag; p 202.

5 Cho, J. Y., Y. H. Lee, et al. (2008). “Difference in migration of placenta according to the location and type of placenta previa.” Journal of Clinical Ultrasound 36(2): 79-84.

6 Magann, E. F., W. E. Roberts, et al. (2002). “Dominant maternal sleep position influences site of placental implantation.” Military Medicine 167(1): 67-69.


UPDATE: Not only did my placenta move by 28 weeks (woohoo!), I revisited the data and re-wrote this post over on Preg U recently. Check it out – Placenta Previa and the Magic of Placental Migration.


  1. TellDrtell

    Placenta races! I love it. I generally favor the underdog in competitions, though, so I might have to get a giant foam… I don’t know, fetus? uterus? that says low-lying placenta. 😉

  2. Pingback: The Mysterious Placenta and the Third Stage of Labour | 42 weeks
  3. thepregnantscientist

    This is a little belated but I should mention that my placenta did migrate!
    It is out of the way (determined at 28 weeks) and my doctor is now not at all concerned about it getting in the way of this baby’s exit.
    One less thing to worry about when I go into labor! phew.

  4. Dinah G.

    Hi there! Just want to let you know that this is an awesome write up explanating everything. It’s probably the only article that put me at ease. I’m 21weeks pregnant and was seen to have a low lying placenta. Although my Dr. did say that it usually moves by the 24th week. So, im feeling hopeful. 🙂 I would like to ask though, is there any precautions your Dr. advised you should take while you wait for the migration? Also, if the cervix has a heathy blood supply, then what are the chances that a low lying placenta will move downwards instead of upwards?

    • thepregnantscientist

      Hi Dinah, I’m glad it could help put your mind at ease!
      My Dr. did recommend pelvic rest until my 28 week ultrasound (which sucks because the 2nd trimester is the trimester of good sex! and, well, “pelvic rest” basically translates into abstinence for the time being). I think that the recommendation is more to avoid the rare rare risk of placental abruption (placenta separating from uterine wall) than to help it with the migration. My placenta was perfectly located in that later ultrasound and I went on to have a natural, vaginal birth without complication.

      As to your question… Hmmmm… I’m not an anatomist but from everything I do know about the cervix, it doesn’t have that same readily accessible, juicy surface blood supply like the uterus does. One thing that I did read (you piqued my curiosity!) is that in the incredible, damn near impossible situation of cervical implantation (seriously, better chance of winning the lottery in every state than having this diagnosis), the embryo usually embeds in the cervix and than taps into the uterine blood supply by digging through the cervical wall. Wow. To me, that implies that the cervix is not really a hospitable place to set up shop and definitely not a big draw for a placenta searching out the best blood supply in the area.

      I hope that helps. I think you have every reason to feel hopeful. All the best and congratulations!!!

      • Dinah G.

        Thank you so much for your reply! 🙂 So, aside from the pelvic rest, you went about your daily activities normally? Or did you have to take things easy?

  5. thepregnantscientist

    Dinah, I went about my daily activities, exercised as usual, didn’t really slow things down. It might depend on the individual diagnosis, though. Might be worth getting more info from your doctor if you are worried.

  6. Ad

    Hello there mothers,

    I am currently 16 weeks and was diagnosed with low-laying placenta at my 15 week of pregnancy.
    Several Dr. advised me to have a complete bed rest!
    Thus in those cases you should speak to your GP, you can not relate to someone else.

    I think I am on complete bed rest, because I had a huge bleeding in my 11 week also a hematoma which healed in 3 weeks.

    I’ve always had brown bleeding once I walk more! So my case is complete bed rest.
    Otherwise the baby is all fine with a strong heart beat 🙂
    I believe the God who created everyone of us will ease my situation soon.

    Thanks for this awesome post.

  7. Drommie

    Thank you for this informative article!! It just makes sense and to me, explains why acupuncture might actually help with this. I, too have been diagnosed with anterior low-lying placenta. I was diagnosed at 20 weeks but told, “Oh, don’t worry, it will move up!” Unfortunately, at 32 weeks, it is 0.7 cm from my cervix and the MFM says there’s NO way it’s moving now and that I WILL have a c-section. I’m trying to hold onto hope. I’m praying hard and doing acupuncture (I also see a chiropractor regularly but don’t know if that will help).

    Anyway, I really appreciated reading this information. It was interesting and encouraging.

  8. Khadija

    Hey, I really loved this article and found it so helpful. At 16 weeks I did an ultrasound and was told I had incomplete placenta previa and that there was a possibility I would have to do a c-section. I was so worried and concerned and started doing research as they told me to limit my physical activities and stop driving which was a rel downer for me. In my online readings I found that it was common for most women placenta’s to be low since as your pregnancy progress the uterine walls stretch causing the placenta to move upwards. I’m 21 weeks now and this ultrasound showed my placenta to be posterior and 4cm away from the cervix. I was still worried but afer reading this article I am hopeful that all will work out eventually as I still have some time. Looking forward to your next article:-) Khadija.

  9. CFATX

    Thanks so much for explaining this! I freaked out when learning about my marginal placenta previa yesterday, and wished I had thought about asking how’s the placenta supposed to move before leaving the ultrasound facility. (We did take time to ask questions with my husband, but the doctor makes you feel so well his time is limited that I missed that one…) Now I wish I knew if my incomplete placenta previa is posterior or anterior. (They didn’t say…) But that’s a big progress already!
    I also meant to ask you: don’t you think it’s crazy science isn’t sure how placentas move?!

  10. stealingnectar

    I just found out at my 20 week scan that I am at risk for having marginal placenta previa. I have had 4 miscarriages already so of course I didn’t want any news of this sort. Thanks for posting this as I found it really helpful. I need to find out more about my case, but you’ve given me the language to ask the right questions at my scan next month. Thank you so much!

    • CFATX

      @StealingNectar: sorry you’re in that situation too! It was very hard for me too to take the news after two miscarriages. The good thing about this is I had an established relationship with an acupuncturist speacializing in fertility issues, and after four sessions with her, the placenta had moved completely out of the way when it was time for the follow up ultrasound, just four weeks after the one that revealed the placenta previa, even though it’s a posterior placenta and this post suggest they tend to move less (my OBG said the contrary, but I suspect she just wanted to be reassuring). Whatever the science proves right, I am sure acupunture did its magic, and I would strongly recommend you would consult an acupunturist!

      • stealingnectar

        I was thinking I might do that after I read this. I think there is an acupuncturist in town that specializes in fertility because I looked him up after one of my four losses. I wish it was all easier, but I appreciate the reassurance and it is good to know it only took yours the four weeks to migrate!

  11. Candice Nalbandian

    Love this article! Puts so much in perspective. I was told this week my placenta is anterior and 2.6 cm away from the cervix but my obgyn wants to see it at 3 cm. So there’s a very good chance it’ll move up and out of the way?

  12. Katie Cirkatiean

    Ok just found this blog and post- thank you for doing this lit review in a fun way! Im also a scientist and had this exact question- I have an anterior placenta and my friend does too. It’s great to be able to understand (potentially) how it moves, how fast And the probability. Thanks again- I’m going to go through and read all your other posts!

    • thepregnantscientist

      Awesome. Thanks! As you might have noticed, I’ve gone a bit dark on this site. My time has been focused on momhood and new ventures, teaming up with friends launching a pregnancy-focused startup called Bloom Life (bye bye academia!)

      I’m starting to build out our content with a Pregnant Scientist soul and I’m always ALWAYS looking for more topics that need a scientist’s touch so please send along suggestions if you have any! email me: molly at bloom.life

  13. Marit

    Love this article, and your blog in general 🙂 I am 12 weeks along with a posterior low-lying placenta. Part personality part my biologist-mindset, but I need things to make sense! Doctor telling me placenta will probably move without being able to explain how drove me up the wall, very grateful for your explanation! Hope you keep blogging!

    • thepregnantscientist

      Thanks! I’m glad it was helpful!

      I’ve moved from academia into the startup world and I’m heading up Content and Community over at Bloomlife now. I keep meaning to put up links to my posts over there (maybe some day I will!) but for now, that’s where they live.

      I’m always open to new ideas for posts if you have any questions that your biologist-mindset is craving answers to – you can email me at molly at bloom.life

  14. Dianne Lavigne

    My daughters incomplete previa moved within a week or two. Since that point she has a episodes of bleeding. Approximately 8 oz and stops within 24 hrs. Happens every 1 1/2 – 2 weeks, My question is, as the ultrasound shows the placenta looks fine, could the quick migration have left a wound and it keeps opening? No other explanation for bleeds.

    • thepregnantscientist

      That’s really interesting, Dianne, and I’m sorry she’s going through that. It must be quite scary. I’m not sure how to answer your question, unfortunately. The placenta is a fascinating thing and science is just at the beginning of understanding its mysteries.

  15. Dr Ranjumoni Konwar

    Really enjoyed it..experienced a more clear understanding of placental tropophism and dynamic placentation

  16. healthiswealthla

    Hi, I found out at 20.5w I have a low anterior placenta as well and I’m freaking out….. 2 questions please if you will, did yours end up moving into a higher anterior position, or did it shift into posterior?
    Also, do you know if anterior placenta carriers experience more frequent cramping and bladder discomfort?

    • thepregnantscientist

      Mine ended up moving higher but still anterior.
      I didn’t have any bladder discomfort (unless you count a small human using it as a punching bag, discomfort) and its hard to know if my cramping was more frequent. Sorry if that doesn’t help!

  17. Saskia S.

    Hi, as a recovering academic with an anterior low-lying placenta at 18 weeks, I so appreciated your inquisitive, informative explanation above. It brought me both clarity and solace, so thank you! I hope to get your take on two nagging, probably embarrassing questions: 1) Any chance that mid-intensity cardio exercise, e.g., stairmaster, running, vigorous walking (though not crazy jumping/HIIT stuff), could jostle the placenta in a way that discourages its upward migration, by exerting extra gravity on our innards as it were? (I’ve read that some doctors are against exercise for women w/ low-lying placentas; what’s their logic?) 2) Could tight clothing around the belly area have any effect on placental location or migration? Thank you, and congrats on your current/recentishly new phase of life career- and kids-wise!

    • thepregnantscientist

      I was advised against exercising and sex. I think the logic was more for the bleeding risk and placental detachment. Perhaps because low lying placenta/placenta praevia are at higher risk for detachment? I really doubt it has anything to do with placental migration. Worth an investigation though!
      I also doubt that tight clothes could have anything to do with it. Seems to be more of an internal effect – stretching or blood supply seeking – than something caused by pressure from the outside.

      These are definitely not nagging or embarrassing questions! There is still so much science doesn’t know about the pregnant body so even these answers can only go so far!

  18. Pingback: My High-Risk Pregnancy Scare: Placenta Previa - TheSanityPlan

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