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Resia Pretorius is a Professor in the department of Physiology, University of Pretoria. She is also Director of the Applied Morphology Research Centre at the University. She has published over 150 research articles in rated scientific journals. She has also been study leader to 28 MSc and PhD students. In December 2011, she was named as winner of the African Union Kwame Nkrumah Scientific Awards for the Southern Region in the category: Basic Science, Technology and Innovation.

Tuesday, May 3, 2011

Thrombosis and Pregnancy



An important issue raised by one of the bloggers is the fact that during pregnancy, there is a tendancy for thrombosis. Remember, stroke can result is either haemorage of a blood vessel or clotting of a vessel, typically formed by fibrin mass or "clot".

During preganancy, the haemostatic status changes, to, amongst others, accomodate and prepare the body for child birth. An important factor here is that the body does not want too much blood loss and therefore, in normal pregnancy there is an increase in procoagulant activity. Also, the fibrinolytic activity (breaking up of fibrin after it has formed) is impaired and remains low during labor and delivery, but returns rapidly to normal, following delivery.

In a 2009 article in Blood, Coagulation and Fibrinolysis, my research team showed ultrastructural changes in fibrin networks found in pregnant individuals and compared this to non-pregnant individuals. Typically thick, major fibers and irregularly placed thin, minor fibers are present in healthy, non-pregnant individuals. In this qualitative assessment, changes in fibrin networks and platelet morphology were studied with scanning electron microscopy in healthy individuals, a healthy individual at 30 weeks pregnancy and post partum. These morphological changes seen during pregnancy might contribute to increased thrombotic risk, because, due to the denser appearance of fibrin networks due to the fine minor network morphology during pregnancy, clots might take longer to be broken down by normal fibrinolytic activity.


E Pretorius, P Bronkhorst, S Briedenhann, E Smit, RC Franz. 2009. Comparisons of the fibrin networks during pregnancy, non-pregnancy and pregnancy during dysfibrinogenaemia using the scanning electron microscope. Blood, Coagulation and Fibrinolysis 20(1):12-16.

PUBMED LINK TO ARTICLE:
http://www.ncbi.nlm.nih.gov/pubmed?term=COMPARISONS%20OF%20THE%20FIBRIN%20NETWORKS%20DURING%20PREGNANCY%2C%20NON-PREGNANCY%20AND%20PREGNANCY%20DURING%20DYSFIBRINOGENAEMIA%20USING%20THE%20SCANNING%20ELECTRON%20MICROSCOPE

28 comments:

  1. A study conducted by researchers in 2008 on changes in clot properties, also concluded that pregnant women have an increased risk for thrombosis. They used Free oscillation rheometry (FOR), which is "a technique that offers an assessment of coagulation properties based on the contribution of all blood components".
    If you have access to EBSCOhost,visit http://0-web.ebscohost.com.innopac.up.ac.za/ehost/detail?sid=9c198878-fb79-45d5-8840-97c3a7f26143%40sessionmgr4&vid=1&hid=17&bdata=JnNpdGU9ZWhvc3QtbGl2ZSZzY29wZT1zaXRl#db=aph&AN=34280770

    OR go to PubMed.gov for an abstract:
    http://www.ncbi.nlm.nih.gov/pubmed/18791944?dopt=Citation

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  2. Will that then be why you should stop smoking while pregnant? Becuase the fibrin network thikens when smoking aswell so it will be a "dubble thikening process".

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  3. How does an oral contraceptive effect the fibrin network? I know that it does cause the "sticky fibres" but how? what is the mechanism behind it?

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  4. Why will clots take longer to be broken down by normal fibrinolytic activity in pregnant women?

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  5. I'm aware of the link between oral contraception and thrombosis, but I'm curious about whether OCs increase the risk / occurrence of varicose veins and whether varicose veins are related to a changed clotting pattern?

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  6. other than immobility, what are the other causes of thrombosis?

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  7. My cousin is currently pregnant, and smokes, so I'd like to know if stopping smoking immediately whilst pregnant is more detrimental for the baby, or if stopping slowly would be better?

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  8. To add on to Tammy's comment, a family friend of mine was smoking 2 packs a day whilst she was pregnant. Her doctor told her that to stop smoking immediately would cause extreme withdrawal symptoms however that these would not have an effect on the baby. That being said, the stress that the withdrawal symptoms may cause could lead to miscarrage. He therefore recommended a gradual cutting down of cigarettes. Could it then be said that the best method of quiting smoking whilst pregnant is entirely dependant on how heavily the mother smokes?

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  9. To add on to Brittany's comment, I have a friend that was pregnant. She was a heavy smoker and she also smoked dagga along with normal sigarets before she knew she was pregnant... A while through the pregnancy a sonar scan showed that the her baby's intestines herniated but did not comletely retract. A week after the baby was born, just before they wanted to opperate to fix the defect, their baby passed away.

    Its does not matter if you stop smoking when finding out you are pregnant, the nicotine is already in the bloodstream and can have severe consequences... some can be fixed while with others it simlpy is too late

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  10. I found this website, which answers a lot of questions regarding trombosis and pregnancy.

    Visit http://www.thrombosis-charity.org.uk/cms/images/stories/File/leaflets/Thrombosis%20And%20Pregnancy.pdf

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  11. Warfarin can be used as an anticoagulation by nonpregnant women, however it is dangerous for women that are pregnant. The reason being, is that it can cross the placenta. There has shown to be a close association between exposure to warfarin in the first trimester and structural bith defects, such as craniofacial and skeletal defects. Exposure in any timester can cause intracranial hemorrhage.

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  12. In the Description above it states that there is a tendency for thrombosis in pregnant women. Just out of curiosity,how often do pregnant women form a fibrin clot,and is it ever deteted before the individual strokes or suffers otherwise? Because if it is a relatively large number of women then something should be done about it..

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  13. Warfarin is prescribed to people who have an increased tendency for thrombosis,and works best in places where blood flows slowly.. Its given to thin blood that pools behind artificial or natural valves, so mostly heart complications,for example atrial fibrilation. So we shouldn't worry too much about pregnant women getting warfarin :)

    I'am also very interested in what Leigh Loubser asked about oral contraceptives,will look into it..

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  14. In the following article that I found the EU consortium EuroCLOT constructed a study to determine whether fibrin phenotypes are hereditary and genetic.

    http://atvb.ahajournals.org/cgi/content/full/29/4/600

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  15. You can learn more about blood coagulation and fibrinolysis on http://journals.lww.com/bloodcoagulation/Fulltext/2009/01000/Comparisons_of_the_fibrin_networks_during.3.aspx

    Vey interesting.

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  16. It is already known that women who are pregnant have an increased risk to suffer from a vein thromboembolism (VTE) but if pregnancy can lead to an increase in the recurence of VTE we did not know. After a study was done they found that a woman who did have VTE previously will have an increased risk to reoccuring thrombotic events when she is pregnant. Fortunately the increased risk is only temporary.

    Journal of the American Society of Hematology
    http://bloodjournal.hematologylibrary.org/content/100/3/1060.full.pdf+html?sid=0cd60b8d-14fd-4196-8e6b-c23d71f7e3be

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  17. It has been found that Low-molecular-weight heparins can be use to treat thrombosis during pregnancy, because the low-molecular-weight heparins cannot cross the placenta and thus it is not harmful to the fetus.

    Treatment of deep venous thrombosis with low-molecular-weight heparin during pregnancy

    http://0-www.sciencedirect.com.innopac.up.ac.za/science?_ob=ArticleURL&_udi=B6T1C-461XFVX-1&_user=59388&_coverDate=04%2F01%2F2002&_alid=1749864602&_rdoc=3&_fmt=high&_orig=search&_origin=search&_zone=rslt_list_item&_cdi=4887&_sort=r&_st=13&_docanchor=&view=c&_ct=22474&_acct=C000005298&_version=1&_urlVersion=0&_userid=59388&md5=944bc5bea4f603092a125444d2ff5bd7&searchtype=a

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  18. A couple of people have already mentioned that sitting for long periods of time, can cause Deep Vein Thrombosis (DVT)- like when flying overseas - and we now also know that being pregnant, increases your risk of developing a blood clot. Thus the chance of DVT for a pregnant woman flying overseas is greater?? If this is the case, do airlines have regulations in place for pregnant women? Do they provide adequate information in the airplane on how to prevent DVT (as well as what it is), like walking around every few hours?

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  19. @ Alieske, flying whilst pregnant does increase your risks of developing DVT and therefore, most airlines will only allow pregnant women to fly up until 35 weeks of pregnancy. They generally also need a note from your physician stating whther you are healthy and fit enough to fly as well as when your due date is. that being said, there is no actual law preventing pregnant women from flying if the trip cannot be postponed.

    http://flyingduringpregnancy.com/DVT_and_Flying_during_Pregnancy.htm

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  20. I found a good article by Krisa Van Meurs, MD an Associate Professor of Pediatrics at Stanford University School of Medicine.

    This article focuses specifically Cigarette Smoking, Pregnancy and the Developing Fetus. Main points in this article are as follows:
    -Nicotine has a half-life of 1 to 2 hours and it is metabolized by the liver and eliminated by the kidney.
    -Nicotine is known to cross the placenta reaching levels in the amniotic fluid and fetus that exceed those of the mother.
    -Nicotine is also measurable in the breast milk of smoking mothers as well as mothers passively exposed to cigarette smoke.
    -Smoking decreases fertility in both men (affecting sperm mobility) and women (affecting ovulation and implantation).
    -Answering my own question asked earlier regarding placental problems and smoking; nicotine reduces the amount of blood flow to the placenta, impairs of the ability of gaseous exchange and reduces the size of the fetal capillaries. These events also results in the lower birth weight of a fetus.

    med.stanford.edu/medicalreview/smrp14-16.pdf]

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  21. Thanks Kylie for referring me. I have always wondered why the risk to suffer a stroke increases during pregnancy. The thickening of the blood now makes sense.

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  22. Dr Pretorius

    Would you mind telling us more about the effects of oral contraceptive? As I am sure the amount of women that take OC's must be just as great if not more than the number of women that smoke. Has any researsh been done on what effect OC's have on the fibrin network? Is it exactly the same as that of a pregnant women? And if so is this really detrimental to the women's health if she does not have a family history of thrombosis? Since pregnancy is a natural phenomenen, could the way your body changes during pregnancy be that bad? The only warning that the packaging gives is that one should not use oral contraceptive if you have a hereditary or aquired predisposition for venous or arterial thrombosis. Are the effects of OC's as severe as that of smoking. Should all women taking oral contraceptives now stop doing so?

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  23. Hi guys!
    So I'm a little behind on this conversation, but I just wanted to add on to Tammy, Brittany and Bernice's comments... My mom smoked while she was pregnant with me and I turned out fine. But then again I do have a tendancy to "seasonal asthma" as the doctor calls it. Could the smoking and the asthma be related?

    Thanx Clarisa

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  24. This comment has been removed by the author.

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  25. Contraceptives and blood clotting:
    It is firstly very important that your doctor prescribes the right contraceptive depending on your medical reason for using an oral contraceptive. (Contraception, hormone imbalance, skin disorders, hirutism, irregular menstrual cycles, polycystic ovary syndrome etc)
    As already mentioned by a few bloggers using an OC enhances your chances of developing a blood clot. These blood clots cause blockage in the veins in your legs and in some cases can travel into your lungs. These blood clots are known as Venous Thromboembolisms (VTE).
    Although there is a chance to obtain blood clots ,it only happens occasionally and it leading to death is very rare.
    There are several factors that influence clot formations whilst using OC:
    1. Age
    2. Obesity
    3. If you are a smoker
    4. Travelling for long periods of time (more than 5 hours)
    5. The type of oral contraception.

    1. With the increase of age is also the increase of your chances having/developing a blood clot.
    2. and 3. If you are obese or smoke more than 40 cigarettes a day, it is advised that you don’t use any OC. Even though you don’t smoke 40 cigarettes a day your chances are still higher than a non smoker to get a blood clot.
    4. As already mentioned by a lot of bloggers, travelling long distances increase your chances of developing VTE. This can be reduced by doing exercise while travelling. (Walk up and down the aeroplane passage, or by wearing elastic hosiery.

    5. The type of oral contraception is where I would like to lay my emphasis on
    There are different types of OC’s available with different hormone compositions.
    *The first OC under discussion is the progestogen only pill, or better known as “mini pill”
    According to Meduse this OC has no or little contribution to increasing blood clots.
    *Combined OC normally consist out of oestrogen and progestogen, and together with 2nd generation progestin, increase your chances by up to 3-4 times.(progestins are classified/grouped in 1st 2nd and 3rd generations)
    *3rd generations OC’s increase your chances up to 6-8 times
    *Oc’s that contain cyroterone (this has an anti-adrogen function) increases your chances more than 8 times for blood clotting to occur.

    In conclusion make sure you are on the right OC. Other factors that are also important to take in to account before using OC’s is if you have a history or family history of blood clotting ,high blood pressure cholesterol and strokes before using OC’s.

    Ps Remember to consult your doctor before you go for any major operations when you are on the pill, sometimes it is preferred to temporary stop use.

    For more information visit

    http://www.medsafe.govt.nz/consumers/leaflets/oralcontraceptives.asp

    http://www.netdoctor.co.uk/medicines/100000754.html

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  26. Refer Clarisa's comment. All theories have exceptions. Outside influences in ones life does play a much bigger roll than is normally accepted.

    I was quite fit and already married for 12 years. During the last 5 years invito was repeatedly done with no success. Both our lives were stress full as it was the late 70’s, al through the 80’s and the early 90’s. Smoking was no stranger and I do believe it can help prevent one from doing something silly – like committing murder, sometimes – if only by keeping your hand busy.

    I was traveling extensively and normally at short notice. This type of living has an effect on the menstrual cycle and only at 5 months of pregnancy discovered the reason for my strange craving for ice (I don’t like ice). I was advised not to stop smoking immediately but to downscale slowly. This I did.

    The result was an active little busy body that later excelled at her sport and academy and drove us crazy with her complex and weird questions. Her only real illness was one season of asma at the age of nine, that was, according to our doctor, because of the heavy scent of orange blossoms in the Lowveld during winter. Normal colds and flu – yes - normally after camping, field trips or sport events.

    Her sister, two and a half years younger, never had asma or any other illnesses except the occasional bouts of colds and flu. Excellent at sport and her studies – like her older sister.

    Every now and then the world gets onto a bandwagon about something – mostly with good reason. Alcohol, breast milk, aspirien, caffeine and nicotine are old time favorites. With all of these there will always be exceptions that must be kept in mind.

    Please carry on the good work – it is quite interesting.

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  27. On average every cigarette you smoke shortens your life with 11 minutes.

    www.netdoctor.co.uk/health_advice/facts/smokehealth.htm

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  28. i think it would be great if an article could be posted about what the effect of hubbly is, because just like the smoking of cigarettes no one is really aware of the major effect it has on your blood plasma and fibrin network. kylie kruger 29085935

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