Chapter 7. Subinvolution and Postpartum Bleeding

This chapter discusses evaluating the bladder and endometrium after delivery or pregnancy loss. Bladder trauma or overextension during labor is common, often delaying the return of normal muscle function. A full bladder can prevent uterine contraction and lead to excess bleeding, so ensuring it is empty is important in postpartum hemorrhage assessment. Transabdominal ultrasound can measure bladder volume without catheterization.

This chapter includes images of retained products of conception to assist in evaluating the uterus during cases of postpartum hemorrhage or abnormal bleeding after pregnancy loss.

OBJECTIVES

By the completion of this Section the participant will be able to:

Recognize clinical signs of subinvolution and/or postpartum abnormal bleeding

Recognize abnormal ultrasound patterns indicating the presence of retained products of conception

Demonstrate measurement of bladder volume with transabdominal ultrasound.

Uterine subinvolution

Subinvolution can occur after birth, or after a miscarriage or uterine evacuation

Causes can be:

Uterine atony (prolonged labor, grand multiparity)

Excessively full bladder (obstructing uterine involution after delivery)

Retained products of conception or placental tissue

Abnormal placentation

Pelvic infection

Signs and Symptoms include:

Prolonged lochia discharge

Irregular or excessive bleeding

Pelvic examination revealing an enlarged and “boggy” uterus

Boivin et al¹ reported that POCUS plays an important role in diagnosing subinvolution with high specificity but low sensitivity when performed in women who have symptoms suspicious of RPOC. Even so, the rapid diagnosis led to expedited treatment times, and shorter length of stays in hospitals. The authors cautioned use of POCUS when discerning findings in early pregnancy bleeding, since a thickened endometrium might be associated with a viable early pregnancy or threatened AB, rather than RPOC after pregnancy loss or elective AB.

Causes of PP bleeding

While postpartum hemorrhage may result from various factors, this discussion will address causes that are identifiable by ultrasound evaluation: specifically, retained products of conception and a distended bladder.

Retained products of conception (RPOC) refers to tissue that remains in the uterus after evacuation from delivery or early pregnancy loss/termination. Postpartum retained products of conception are more likely to occur after a preterm birth, since the placenta does not release as readily.

Distended bladder

A distended bladder postpartum can form an obstruction for the uterus to involute normally. The first thing to evaluate is the size of the bladder. To check for incomplete bladder emptying as an alternative of catheterization, use ultrasound to measure volume—calculated as length (L) × depth (D) × width (W) in cm. The bladder looks eggplant-shaped in the sagittal view and rectangular in the transverse plane.

Image 1, 2. Images demonstrating how to measure bladder volume.

The calculation is: L X D X W, times 0.52. Another way to get an estimate is to multiply L X D X W and divide it by 2. This will give you results in cc (or cubic centimeters).

Figure 1, Images 3, 4, 5. Images demonstrating bladder volume measurement and calculation.

Figure 1 (above) demonstrates how a bladder is measured using the correct formula.

Image 6. Image depicting identification of urine jets into the bladder observed while scanning.

Image 6 demonstrates how to use color flow to validate that this structure is the bladder, where it shows movement or flow of fluid into the bladder from the ureters (“urine jets”).

Uterine appearance after delivery²

The features to assess are both the uterine size, and the endometrial thickness and echogenicity. A uterus begins to decrease in size within a few weeks and is usually back to normal size by 6-8 weeks after delivery. Areas of mixed echogenicity are normal and can persist for several weeks after delivery.

Endometrial thickness varies, however, and studies have not demonstrated normal ranges of thickness. If there is a thin endometrium, this precludes the possibility of RPOC. One study reported by Norton found that in an endometrium less than 10mm in thickness, it is rare to have RPOC. A focal mass in the endometrium could represent tissue, or a blood clot. Color Doppler demonstrating blood flow within a focal mass is suggestive of RPOC, but even if there is no color flow, RPOC could still be present. So color Doppler is an adjunct to assessing for RPOC, and the clinical picture of heavy or persistent bleeding is likely to be more diagnostic.

Figure 2. Illustration of potential causes of postpartum abnormal bleeding.

Ultrasound appearance of uterus within first 24 hours PP³

The uterine cavity can have large volume of echogenic material, especially in the lower uterine segment. (up to 54.3 cc) and no correlation with pathology. The presence of extra material in the uterus was not predictive for RPOC, however. Even in the presence of color Doppler, appearance of RPOC is highly variable.

Ultrasound appearance of uterus after 24 hours PP

In reviewing studies of women with normal postpartum bleeding there was an echogenic mass seen in 51% on PP day 7, and in 21% on day 14, and in 6% on day 21. ³This study did not correlate the ultrasound findings to heaviness of the bleeding, So although the conclusion was that the presence of a mass did not always indicate RPOC, it remained questionable as to whether the predictive value would have been increased with use of color Doppler. When surgically removed tissue was evaluated there was definite correlation with use of color Doppler, increasing the predictive value.

Causes of postpartum bleeding – retained placenta

After assessing for a full bladder, an ultrasound can evaluate the texture of the endometrium, as well as the general size of the uterus. Since emptying a full bladder would be the first step in managing immediate postpartum hemorrhage, it makes it more difficult to see the uterus as clearly as with a full bladder. If bleeding is being evaluated days or weeks later, a full bladder would be helpful for imaging.

Figure 3. Common findings related to retained placenta.

Results are often nonspecific, as blood clots and retained products appear similar. The main finding is an endometrial mass. Color flow indicates live tissue; clots lack blood flow, but retained products often show stalk-like or diffuse flow in the mass or endometrium.

Image 7. Irregular, thickened endometrium, globular uterine shape.

Image 8. Close-up image of irregular cystic thickened endometrium.

The images above (image 7 and 8) may show the uterus a few days after vaginal birth. The endometrium is thickened with no color flow, but there are no standard parameters for the involuting uterus. Both uterine size and endometrial thickness vary. While it's expected that the endometrium appears thin post-delivery, it usually remains thick due to ongoing lochia shedding and residual clots.

The uterine cavity need not be completely flat after delivery, but it should not be distended like in this image. Clots can occur, making it hard to distinguish them from placental tissue; color flow imaging helps with differentiation.

Images 9, 10. Images of cystic, thickened endometrium (left) and identification of blood flow into the endometrium (right); highly suggestive of retained products of conception.

Images 9 and 10 show a mass in the endometrium with active blood flow, suggesting retained placental tissue.

Images 11, 12. Images of thickened endometrium demonstrating color flow.

Images 11 and 12 show thickened, cystic endometrium, also demonstrating color flow to the suspicious area.

Post early pregnancy loss

Image 13. Post pregnancy loss, measurement of endometrium showing it to be thin and empty, indicating complete emptying.

Images 13 and 14 show an empty endometrium, which is an expected finding complete evacuation after pregnancy loss. The image on the right below (image 15) displays a thickened endometrium that warrants additional evaluation, particularly in cases of abnormal uterine bleeding. The endometrium appears irregular with mixed echogenicity. Heavy bleeding suggests incomplete shedding of tissue. Color flow imaging can help identify any remaining tissue with active blood supply, such as placental or conception products.

Images 14, 15. Images comparing a thin post pregnancy loss endometrium wtih an abnormal thickened endometrium.

Images 16, 17. Images of endometrium post early pregnancy loss, in both sagittal and transverse views.

The images above (16 and 17) show fluid in the endometrium along with mixed echogenicity, which suggests a failed pregnancy. Persistent bleeding after miscarriage or treatment may indicate retained tissue with blood supply, requiring further medication such as misoprostol or referral to a specialist for management.

Images 18, 19. Images of endometrium following early pregnancy termination, image on the left without color flow, image on the right using color flow to identify blood flow to the area.

In the retroverted uterus below (image 20) there is irregular thickening and mixed echogenicity of the tissue. This could mean there are remaining pieces of tissue other than clots in the uterus. If the woman has not yet miscarried, this could be expectantly managed by repeating the ultrasound again in a week. If she is bleeding heavily, then consultation with an advanced provider is necessary.

Image 20. Image of a retroflexed uterus after a pregnancy loss, with mixed echogenicity and fluid in the endometrium, suggestive of retained products of conception.

Fluid in the endometrium does not always indicate retained products, but bleeding might appear like this before a clot forms.

Images 21 and 22 show what one might expect to see after an early pregnancy loss as there remains some bleeding, even though the endometrium does not appear very thick.. Even if the endometrium appears normal, it is important to place color or doppler flow in the area to look for small areas of blood flow that might otherwise be missed.

Images 21, 22. Images of subtle signs of blood flow into a relatively thin endometrium following an SAB, even though the endometrium is not thickened.

Images 23, 24, 25. Additional aimages of thickened, cystic endometrium.

Images 23-25 are all from the same woman, showing cystic endometrium. Ongoing bleeding may suggest endometrial hyperplasia rather than post-miscarriage. A pregnancy test is recommended, as results can remain positive for weeks after a pregnancy ends.

Image 26. Image of a post-SAB endometrium with an ovoid density (green arrow) and color flow into that region.

Ultrasound imaging in image 26 shows a thickened, echo-dense area within the endometrium (green arrow) that demonstrates blood flow. Although the overall endometrial depth is within normal limits, this density warrants further evaluation. If there is any uncertainty, consultation with an advanced clinician is recommended.

SUMMARY

Subinvolution is one of the primary causes of maternal postpartum hemorrhage.

This can be caused by either distended bladder or inadequate expulsion of placenta or products of conception

Ultrasound is a useful tool in evaluating the status of both the maternal bladder and the endometrium after birth or pregnancy loss.

Bladder volume can be calculated by multiplying length X depth X width and then dividing by 2

Women's Point-of-Care Ultrasound: Second and Third Trimester

Subinvoluition and Postpartum Bleeding