The ultrasonography report of a pregnant client reveals the presence of polyhydramnios

The 4Ts of postpartum hemorrhage (PPH) +1: tone, trauma, tissue, thrombosis, and traction. More than one of these can cause postpartum hemorrhage in any given patient.

"Tone"

Atony is by far the most common cause of postpartum hemorrhage. Uterine contraction is essential for appropriate hemostasis, and disruption of this process can lead to significant bleeding. Uterine atony is the typical cause of postpartum hemorrhage that occurs in the first 4 hours after delivery.

Risk factors for atony include the following:

  • Overdistended uterus (eg, multiple gestation, fetal macrosomia, polyhydramnios)

  • Fatigued uterus (eg, augmented or prolonged labor, amnionitis, use of uterine tocolytics such as magnesium or calcium channel blockers)

  • Obstructed uterus (eg, retained placenta or fetal parts, placenta accreta, or an overly distended bladder)

"Trauma"

Trauma to the uterus, cervix, and/or vagina is the second most frequent cause of postpartum hemorrhage. Injury to these tissues during or after delivery can cause significant bleeding because of their increased vascularity during pregnancy. Vaginal trauma is most common with surgical or assisted vaginal deliveries. It also occurs more frequently with deliveries that involve a large fetus, manual exploration, instrumentation, a fetal hand presenting with the head, or spontaneously from friction between mucosal tissue and the fetus during delivery. Cervical lacerations are rarer now that forceps-assisted deliveries are less common. They are more likely to occur when delivery assistance is provided before the cervix is fully dilated.

Risk factors for trauma include the following:

  • Delivery of a large infant

  • Any instrumentation or intrauterine manipulation (eg, forceps, vacuum, manual removal of retained placental fragments)

  • Vaginal birth after cesarean section (VBAC)

"Tissue"

Retained placental tissue is most likely to occur with a placenta that has an accessory lobe, deliveries that are extremely preterm, or variants of placenta accreta. Retained or adherent placental tissue prevents adequate contraction of the uterus allowing for increased blood loss.

Risk factors for retained products of conception include the following:

  • Prior uterine surgery or procedures

  • Difficult or prolonged placental delivery

  • Signs of placental accreta by antepartum ultrasonography or MRI

"Thrombosis"

During the third stage of labor (after delivery of the fetus), hemostasis is most dependent on contraction and retraction of the myometrium. During this period, coagulation disorders are not often a contributing factor. However, hours to days after delivery, the deposition of fibrin (within the vessels in the area where the placenta adhered to the uterine wall and/or at cesarean delivery incision sites) plays a more prominent role. In this delayed period, coagulation abnormalities can cause postpartum hemorrhage alone or contribute to bleeding from other causes, most notably trauma. These abnormalities may be preexistent or acquired during pregnancy, delivery, or the postpartum period.

Potential causes include the following:

  • Platelet dysfunction: Thrombocytopenia may be related to preexisting disease, such as idiopathic thrombocytopenic purpura (ITP) or, less commonly, functional platelet abnormalities. Platelet dysfunction can also be acquired secondary to HELLP syndrome (hemolysis, elevated liver enzymes, and low platelet count).

  • Inherited coagulopathy: Preexisting abnormalities of the clotting system, as factor X deficiency or familial hypofibrinogenemia

  • Use of anticoagulants: This is an iatrogenic coagulopathy from the use of heparin, enoxaparin, aspirin, or postpartum warfarin.

  • Dilutional coagulopathy: Large blood loss, or large volume resuscitation with crystalloid and/or packed red blood cells (PRBCs), can cause a dilutional coagulopathy and worsen hemorrhage from other causes.

  • Physiologic factors: These factors may develop during the hemorrhage such as hypocalcemia, hypothermia, and acidemia.

"Traction": The traditional teaching is that uterine inversion occurs with an atonic uterus that has not separated well from the placenta as it is being delivered, or from excessive traction on the umbilical cord while placental delivery is being assisted. Studies have yet to demonstrate the typical mechanism for uterine inversion. However, clinical vigilance for inversion, secondary to these potential causes, is generally practiced. Inversion prevents the myometrium from contracting and retracting, and it is associated with life-threatening blood losses as well as profound hypotension from vagal activation.

Ultrasonography is the main modality for the diagnosis of polyhydramnios and evaluation of the fetus. Features that are assessed in polyhydramnios include amniotic fluid, possibly because of multiple pregnancy, chorionicity in multiple pregnancy, fetal macrosomia, fetal thorax, fetal central nervous system, fetal gastrointestinal tract, cervical length, and posttreatment follow-up results. [10, 6, 7]  There are 2 methods by which amniotic fluid can be assessed with ultrasonography: (1) single deepest vertical pocket (DVP) of amniotic fluid, with polyhydramnios defined as 8 cm or more, or (2) the amniotic fluid index (AFI) ,with polyhydramnios defined as ≥24 cm or more. [1, 2, 3, 4, 5]

The increase in amniotic fluid, in many of cases, can be attributed to impaired fetal swallowing or the overproduction of fetal urine due to a high-output cardiac state, renal abnormality, or osmotic fetal diuresis. [1, 2, 3, 4]

The degree of polyhydramnios is frequently categorized as mild, moderate, or severe, based on an AFI of 24.0–29.9 cm, 30.0–34.9 cm, and ≥35 cm, respectively, or a deep vertical pocket of 8–11 cm, 12–15 cm, or ≥16 cm, respectively. [1, 2, 3, 4]

There are at least 3 methods for measuring amniotic fluid: (1) depth of the deepest vertical pool, (2) the 2-diameter pocket (depth X width of the longest pocket), and (3) the amniotic fluid index (AFI). [11, 12, 13, 14, 15, 16]

With the AFI method, the uterus is divided into 4 quadrants. The depths of the deepest vertical pools in the 4 quadrants are measured and added to give the index. [17] Occasionally, at less than 20 weeks' gestation, only the right and the left lower quadrants are used. The normal index is 5-24. In polyhydramnios, it is more than 24. AFI of a normal population (ie, normative values) corresponding to the gestational age can be noted, and the percentile value of the particular patient can be calculated by using the mean and standard deviation.

The graph below shows the normal limits of AFI based on gestational age. The mean AFI for normal pregnancies is 11-16 cm. Polyhydramnios is diagnosed when the AFI is more than the 95th percentile value. Normative values are not available before 16 weeks' gestation.

The ultrasonography report of a pregnant client reveals the presence of polyhydramnios
Graph illustrating amniotic fluid index in a normal singleton pregnancy. The solid line is the mean AFI, the lower dotted line is the 5th percentile value, and the upper dotted line is the 95th percentile value (data adapted from Moore, 1990). Image courtesy of Christopher L. Sistrom, MD.

The incidence of polyhydramnios can vary with the technique used. A single deep pocket more than 8 cm is diagnostic of polyhydramnios. With the single-pocket technique, the incidence is 0.7% (1.1% for oligohydramnios). With the 2-diameter pocket, the rate is 3% (30% for oligohydramnios), and with the AFI method, the rate is 0% (8% for oligohydramnios). Therefore, the single-deep-pocket method is the best technique because it classifies the least number of cases as being abnormal.

A simple rule of thumb is that in the first trimester, the fluid is more than the embryo/fetus; in the second trimester, the fluid is equal to the fetus; and in the third trimester, the fluid is less than the fetus.

Twins can be monochorionic or dichorionic. The difference can be assessed by careful observation. In dichorionic twins, the intermembrane septum is thick, with 3 or 4 membrane layers, and the membrane is more than 2 mm. The triangular sign is present and very specific. In dichorionic twins, the cause of polyhydramnios is the same as that in a singleton pregnancy.

In monochorionic twins, the intermembrane septum is thin, and the junction of membranes forms a T shape. In monochorionic twins, the most common cause of polyhydramnios is twin-to-twin transfusion syndrome

Ultraonography may be useful in screening for growth retardation. In a study by Eroglu et al of polyhydramnios-complicated pregnancies in the third trimester, the accuracy rate of fetal weight estimation with ultrasonography was found to be high for both automated and manual measurements, but automated tools were found to have a higher success to predict estimated fetal weight (EFW). [1]

Ultrasonography may be helpful in evaluating the mouth, stomach, small bowel, and abdominal wall.

One technique involves the change in bladder dimension observed over 20-minute intervals. These changes can differentiate fetal polyuria from other causes of polyhydramnios. However, this technique has its limitations. It underestimates the degree of fetal urine production by at least 50%, and it is not useful in severe hydramnios because the bladder is already filled with urine, and any further increase in the bladder size is minimal. [18]

Cervical length is essential for assessing the risk of preterm labor. If the fetus is less than 24 weeks' gestation and if after amniotic drainage the cervical length is less than 25 mm, a cervical suture is required to prevent preterm labor. [19]

The AFI should be monitored twice a week when the patient is being treated with indomethacin. The treatment is stopped when the AFI is less than normal. The response is seen usually between 4 and 20 days.

Doppler imaging of the ductus arteriosus is also done within 24 hours of starting treatment and once weekly thereafter. Indomethacin is known to cause premature closure of ductus arteriosus, and if this happens, indomethacin is stopped.

The values for amniotic fluid index, single deepest pocket, and 2 diameter pockets are not normally distributed throughout pregnancy. Therefore, a logarithmic transformation is required for gestational age–specific ranges. Normative values also vary within a population.

The incidence of detection of polyhydramnios varies with the technique used.

Ultrasonographic assessment of amniotic fluid is a poor indicator of amniotic volume. The 95% confidence limit is wide compared with the dye-dilution technique for the measurement of amniotic fluid volume.

Magann et al showed that while sonography and the single-deep-pocket method are good for measuring normal amniotic fluid volume (83-94%), they are not accurate in diagnosing polyhydramnios (33-46%) and oligohydramnios (11-27%). [12, 13]

If color Doppler imaging is used along with normal scanning, the AFI is less than that obtained without Doppler techniques. This difference increases the diagnosis of oligohydramnios.

Chorioangiomas larger than 5 cm can produce complications such as polyhydramnios, preeclampsia, preterm delivery, congenital malformation, congestive cardiac failure, antepartum hemorrhage, intrauterine growth retardation, and microangiopathic hemolytic anemia.

Ultrasonograms show a placental mass with anechoic spaces, which demonstrate flow on color Doppler studies and pulsatile flow on spectral Doppler trace studies.