Optimizing implantation. Why does a thin endometrium (uterine lining) result in lower implantation?

For successful implantation to occur an embryo needs a “receptive” uterine lining.  In a previous blogs, Katie Koss and Janet Chiarmonte have discussed the various pathologies that can prevent implantation and the three common techniques used to evaluate the uterine cavity.  In this blog, the importance of measuring endometrial (lining of the uterine cavity) thickness during cycle monitoring will be discussed.

The endometrium responds to estrogen by growth in its glands and the surrounding tissue (stroma).  This is reflected on ultrasound by an increase in thickness and formation of a triple-line endometrial pattern.   When ovulation occurs, or when progesterone is started, a “secretory” change occurs in the endometrium, which then becomes receptive for implantation.

What is “normal” endometrial thickness?

There is no definite cut-off level below which implantation will not occur.  The consensus seems to be >7 mm in cross-section, with a triple-line endometrial pattern.  An endometrial thickness <6 mm is associated with a lower rate of full-term pregnancy.  Other publications suggest that thickness >9 mm is important.

Slide1What are the causes of a “thin” endometrium?

  • Scar tissue inside the uterine cavity (intrauterine adhesions or Asherman’s syndrome) may result in a thin lining.
  • Other causes include medications such as clomiphene citrate, which can cause depletion of endometrial estrogen receptors.
  • Prolonged use of birth control pills will also result in a thin uterine lining.
  • In a large number of patients, there is no apparent cause for a thin endometrial lining.

Why does a thin endometrium result in lower implantation?

Several theories have been proposed to answer this very important question

  • Estrogen receptor abnormalities.  For the uterine lining to grow, estrogen has to bind with estrogen receptors.  If these receptors are abnormal, the lining will not grow
  • Oxygen tension theory.

Slide2In a recent publication (Fertil Steril 2011;96:519-521), Dr. Robert Casper from the University of Toronto, Canada offers an interesting mechanism by which a thin lining results in lower implantation. The uterine lining has two layers, a “functional” layer which gets shed with menstruation and a “basal” layer which persists.  The functional layer of the endometrium has plenty of small blood vessels (capillaries), in contrast to the larger spiral arteries in the basal layer.  With ovulation, there is constriction of the spiral arteries with reduced blood flow to the functional layer.  This results in reduced oxygen tension, which is good for embryo implantation.  In the endometrium, when the thickness measured by ultrasound is <7 mm, it is the functional layer that is thin or absent, and the implanting embryo would be much closer to the spiral arteries and the higher vascularity and oxygen concentrations of the basal endometrium. The high oxygen concentrations near the basal layer could be detrimental compared with the usual low oxygen tension of the surface endometrium.  Interesting!

In my next blog, we will discuss the various treatments that have been tried to correct a thin endometrial lining.

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36 Responses to Optimizing implantation. Why does a thin endometrium (uterine lining) result in lower implantation?

  1. Commenter says:

    I have been diagnosed with a thin endometrium lining. I had 2 miscarriages and 1 was an ectopic pregnancy. I have a 7 years old daughter and never had problems with my 1st pregnancy. What new treatment options do you have?

    • You need to be investigated for the thin lining. You should have a hysterosonogram or hysterosalpingogram to rule out scar tissue in the uterus. Please consult with a Board Certified Reproductive Endocrinologist to get more specific advise.
      Dr V Karande

  2. Anonymous says:

    Jst got diagnosied with a thickend endometrium(19.1),free fluid in pod n my right ovary I enlargend..I am congused can u help me know what exactly I would b suffering from and how to get myself health again please

    • You may have just ovulated. We often see a cyst on the ovary (it is the corpus luteum — what’s left behind in the ovary after the egg is released) and free fluid behind the uterus (cul de sac).

      Another possibility is you may have an endometrial polyp. For that diagnosis to be confirmed, you need a hysterosonogram, hysterosalpingogram or a hysteroscopy.

      Please reconsult with your physician to get a more specific answer.
      Dr V Karande

  3. Commenter says:

    My endometrium lining is sitting at around 4.5 on day 16. I am on 10mg Progynova and 2x 100mcg Estraderm Transdermal Patches every 3 days.
    Apparently I am not responding to the medication and that is why the endometrium isnt thickening up.

    I have a 10 year old daughter with no complications. We had a very successful round with IVF getting 5 frozen embryos but cannot do anything with them as my lining will not thicken up.
    Do you have any suggestions?

    • Please get specific advise from your physician.
      At InVia, we would add Estrace (estradiol) 2 mg vaginally twice daily for a week and reassess. The estrogen gets absorbed through the vaginal walls and directly reaches the uterine lining.

      Hope this helps.
      Dr V Karande

  4. Commenter says:

    I have had two miscarriages in 2012, and have not been able to get pregnant in over a year. I have a thin uterine lining measuring at 4mm before ovulation, and 5mm right before my period. I have a high progesterone level (18) and didn’t respond to progesterone supplement. Can you recommend what other medications can thicken my lining? Also, would you recommend a HSG or hysteroscopy for me?

    • I am sorry about your miscarriages. Have you had a work up for the miscarriages? Some of the tests that may be useful are chromosomes (you + husband), immune labs (to rule out antiphospholipid antibody syndrome), cavity check (hysterosonogram, hysterosalpingogram or hysteroscopy) and hormones (FSH, LH, E2, TSH, fasting prolactin).
      A thin lining can be secondary to adhesions in the uterine cavity (which can occur after a D&C). Please have a cavity check (see above) to rule out adhesions.
      Please consult with a fertility specialist for more specific advice. We would welcome you as a patient at InVia.
      Dr V Karande

  5. Commenter says:

    I was a gestational carrier in 2009 and had a great lining (10-12mm). After the baby was born I got on birth control. I am currently working on another surrogacy. We were cycling in July and August but my lining would not exceed 5.5mm. We decided to discontinue birth control to give my body a chance to regulate on it’s own before we proceed with our next FET.

    After stopping birth control I had 2 short anovulatory cycles. I am now on my 3rd cycle and I finally ovulated. Is this a sign that my lining may be cooperating again? Or should we wait a few more months?

    • To be able to answer this question, I need to understand why your lining was thin. Birth control pills usually do not affect lining thickness once the patient has stopped taking them. Have you had a cavity check to rule out intrauterine adhesions?
      I see no point in waiting a few more months.
      Perhaps your physician may want to do a “mock cycle” where you take the medications as if you were doing a real cycle and an endometrial biopsy is done 7 and 12 days after starting progesterone to see if the lining is “in phase”.
      Dr V Karande

  6. Clomid? says:

    How long after stopping clomid does it take the endometrium to recover? Does Femara affect it at all?

  7. Lo says:

    How long does it normally take the endometrium to thicken after stopping birth control? My ultra sound showed my endometrium at 0.563 cm being on the pill for 7 years and im 37.

    • Hi Lo
      I am presuming you were taking regular (daily dose) birth control pills and not some of the long acting medications.
      The lining should “thicken” in the very first cycle after stopping the pills.
      The hormones in birth control pills are short acting (which is why you have to take them daily). When you stop the pill and get a menses, the lining that is affected by the birth control pills is shed.
      The “new” lining is bereft of any influence from the birth control pills and should “thicken” normally.
      Are your periods regular when you are off the pill? Your lining of 5.63 mm is normal for the early follicular phase of the cycle (days 3 – 10). As you approach ovulation, the lining will often get thicker and develop a tri-laminar (three-layer) pattern.
      I plan to write a blog about this in the near future.
      Hope this helps.
      Dr V Karande

  8. Lo says:

    How long does it take the endometrium to thicken to normal mm after stopping birth control pills? mines is 5.6mm after being on birth control for 7 years.

  9. Clomid 50 mg says:

    Can clomid 50mg cause thinning of the endometrial lining I on my 2 nd cycle of clomid and my period is unusually light bleeding I have right fallopian blocked tube and been trying to conceive for 2.5 years im 35 yrs old but doctor would not do laparoscopy and wants me to take clomid 50mg for 6 months- scared about side effects though my progesterone level went up to 51 from8.5 on my 21 day cycle .. Suffering from severe menstrual cramps an getting worst as I get older.. Please help..

    • Yes, clomiphene citrate is an anti-estrogen and can cause thinning of the endometrial lining.
      Please discuss tubal catheterization as an option with your doctor.
      Clomiphene citrate along with timed intra-uterine inseminations has a higher pregnancy rate than with intercourse alone. Most of the pregnancies are in the first 3 – 4 cycles after which other options need to be discussed.
      Your menstrual cramps could be secondary to endometriosis. This by itself could be an indication for laparoscopy in your case.
      If your physician is not giving you satisfactory answers, please get a second opinion.
      We would welcome you as a patient at InVia.
      Dr V Karande

  10. Commenter says:

    I had a D&C Suction 3 weeks ago. I am emotionally ready to start trying to conceive again, but I’m scared that my uterine lining is not thick enough to sustain a pregnancy. Is this an issue or should my uterine lining thickin back up in 3 weeks?

  11. Commenter says:

    Please advise recently got ultrasound scan report which shows Uterine linning of 2mm on day 11 of the menstrual cycle. I also completed clomid

    • I do not have enough information to give you specific advice.
      A 2 mm lining is something that needs further investigation.
      This is so especially if it is a persistent finding.
      Clomid does cause the endometrial thinning, but the effect is transient.
      You need to have a hysterosonogram, hysterosalpingogram or a hysteroscopy.
      Intrauterine adhesions need to be ruled out.
      Dr V Karande

  12. Commenter says:

    I am having an FET in a week and my lining is maintaining around 6.7 to 6.5 mm. We have decided to transfer two blastocysts. Is there a chance of success with lining around 6.5 mm and what are the odds?

    • 6.5 mm would be considered an acceptable endometrial thickness at InVia.
      If your clinic statistics suggest otherwise, you may want to consider taking estradiol tablets vaginally for a week to see if it improves.
      Dr V Karande

  13. Commenter says:

    Is it possible to ovulate too early for the endometrium to be ready for a blastocyst? I am 36 years old and am naturally ovulating around CD10 now (25 day cycle.) Or do the hormones that control ovulation also force the endometrium to be ready? If so, is there a way to correct this?

    • Nothings broken, so nothing to fix.
      Your fertile days are the 4 days prior and the one day after ovulation.
      In your case, that would be days 6 – 11.
      Ovulation triggers a series of hormonal changes which will make the endometrium receptive for implantation. In your case, this would be earlier than someone who ovulates on, say, day 14.
      Dr V Karande

  14. Commenter says:

    what is the cause of breast heaviness and pain?

    • I am assuming you are in excellent health and your breast exam etc is normal.
      Progesterone, which is released in the second half of the cycle (after ovulation) can cause the breasts to feel heavy.
      Pain is unusual — please get yourself checked.
      Dr V Karande

  15. Commenter says:

    Hi, I was on Depo Provera for 16 years my last shot was April 2013 during my 16 years on the depo I did not get a period and I still don’t have one after almost 1 year of stopping the shot. Do Depo cause a thin uterin lining and what should I do to thickend? Also can I ovulate without having a cycle?


    • It can take up to a year for the effects of Depo Provera to wear off. You have taken it for a long time and I guess it has done its job of preventing pregnancy.
      You can have a thin lining from Depo Provera.
      There are two options for you — one is to wait. The other is to proceed with ovulation induction and see if you respond.
      Yes, you can ovulate without having a cycle.
      Please consult with a Board Certified REI for specific advice.
      We would welcome you as a patient at InVia.
      Dr V Karande

    • Hi Mrs Desai
      We have had several pregnancies without a three-layered pattern.
      I therefore do not think it is a serious issue.
      Please make sure you have had a cavity check (HSN, HSG or hysteroscopy) and it is normal.
      Dr V Karande

  16. Commenter says:

    I had history of unexplained intrauterine filmy adhesions
    were they been removed with no forming back on 6th hysteroscopy using intercot jell and it worked !!!!

    throughout i had lining issue my lining was 2.5mm same cycles 4mm i was on all types of estro meds, Viagra , Tamoxifen …etc.

    I had 1st IVF last month 3 blast ET with 6.5mm lining my lining improved it always respond to my own estrogen (hmg stimulation) i started crying when the nurse told your lining is 6.4 i never heard that number, but ended with m/c after 4weeks.

    what kind of test do u think doc will help to prevent the m/c next cycle also i heard that the quality is more important then the thickness od lining pleeeease help me ive asked my doc for lining biopsy but he said no need, i can send u my surgery videos if required

    • I generally avoid giving specific advice in complicated cases as part of a blog post.
      Your situation is indeed unusual to require 6 hysteroscopies to remove “unexplained intrauterine filmy adhesions”
      I also understand your disappointment regarding the miscarriage.
      15% of pregnancies result in miscarriage (31% if you count chemical pregnancies).
      If this was your only miscarriage, my best advice to you is to try again.
      Dr V Karande

About Dr. Vishvanath Karande

Dr. Karande is Board Certified in the specialty of Obstetrics and Gynecology as well as the subspecialty of Reproductive Endocrinology and Infertility. He is a Fellow of the American College of Obstetricians and Gynecologists and Member of the American Society for Reproductive Medicine.

View all posts by Dr. Vishvanath Karande →

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