What is the amniotic cavity and what are the fetal membranes?
The fetus lives within a fluid cavity (the amniotic cavity) (bag of waters) contained by two membranes: the inner membrane, closer to the fetus, called the amnion and the outer membrane, called the chorion. The fluid within the amniotic cavity comes from the fetus, the membranes and the umbilical cord early in the pregnancy and is mostly made of fetal urine after 16 weeks. Fluid within the fetal lungs also enters the amniotic fluid.
Early in the pregnancy, the uterine cavity is bigger than the amniotic cavity, which leaves a gap between the amnion surrounding the fetus and the chorion which is attached to the inside of the uterine wall. At approximately 16 weeks, the amnion has reached the wall of the uterus and the space between the amnion and the chorion (the chorionic cavity) becomes obliterated. On ultrasound, the separation between the membranes can be seen in the first trimester, but should not be seen from 16 weeks on.
Why and how are invasive procedures done?
Access to the uterine cavity or to the fetus is sometimes necessary for diagnostic or for treatment purposes. For example, amniotic fluid may be obtained for genetic studies, or the fetus may need a blood transfusion or other treatments that require entering the amniotic cavity or the fetus itself. Access to the amniotic cavity involves the insertion of a needle or other wide bore instrument under ultrasound guidance. The needle or instrument must traverse the fetal membranes to get to the amniotic cavity or to the fetus.
Why does the bag of waters not break after an invasive procedure?
After the diagnostic or therapeutic procedure is done, the needle or instrument is pulled out of the amniotic cavity. In most cases, fluid from the amniotic cavity does not escape the bag of waters, as the amnion and the chorion remain attached to each other and to the wall of the uterus.
Why can there be leakage of fluid after an invasive procedure?
In a small proportion of cases, fluid may escape between the amnion and the chorion or between the chorion and the uterine wall. If the fluid accumulates between the amnion and the chorion, but the chorion remains attached to the uterine wall, the patient will show detached membranes on ultrasound, but there will still be a normal amount of fluid in the uterus and fluid will not leak from the vagina. On the other hand, if the fluid leaks outside the chorion, it can track down to the cervix and to the vagina, and the patient will complain of leakage of fluid.
What is iatrogenic preterm premature rupture of membranes (I-PPROM)?
Leakage of fluid per vagina after an invasive procedure is called "iatrogenic" (resulting from the medical intervention). Because such complication typically occurs before 37 weeks (term pregnancy), the complication is called iatrogenic preterm premature rupture of membranes, or I-PPROM. Previable I-PPROM refers to I-PPROM before the fetus is viable. The likelihood of I-PPROM occurring is approximately 0.6-3:1000 after amniocentesis, 5% after operative fetoscopy and up to 80% in more complicated surgical procedures. Procedures that do not involve entering the amniotic cavity, such as chorionic villus sampling (CVS), should typically not result in leakage of fluid, unless the amniotic cavity has been entered unintentionally or a different complication has ensued.
What is the prognosis after I-PPROM?
In many cases, leakage of fluid after an invasive procedure may cease within a week. In such cases, the leakage of fluid is typically a small amount and the amniotic does not appear significantly reduced on ultrasound. If the leakage of fluid ceases spontaneously, the pregnancy may continue without any further treatment.
In other cases, however, the leakage does not stop and the patient continues to leak fluid per vagina. In such cases, ultrasound shows decreased amniotic fluid volume. Continued leakage of fluid per vagina may result in miscarriage, premature delivery, fetal or neonatal death. Infection of the amniotic cavity may occur from bacteria that ascend from the vagina and result in uterine contractions and labor. The absence of an adequate amount of fluid around the fetus may also hinder the normal development of the lungs (pulmonary hypoplasia), particularly if the I-PPROM occurs earlier than 18-20 weeks, as normal fetal lung development requires an adequate amount of amniotic fluid around the fetus. In such cases, even if the pregnancy reaches viability, the baby may not survive because of lack of lung development. The overall perinatal mortality of previable PPROM managedexpectantly is 60%. Nearly one third of these deaths occur in the womb. Poor lung development (pulmonary hypoplasia) occurs in 50% of cases diagnosed prior to 19 weeks.
What are the management options after I-PPROM?
Patients with I-PPROM are typically counseled to consider one of two standard options:
A) Not to continue the pregnancy. In countries or States where this is permissible, the patient may elect this option within the legal limits of the location. The rationale behind such decision is based on the fetal and/or maternal complications that may occur from prolonged leakage of fluid per vagina. Fetal complications include death or prematurity and complications of prematurity. Maternal complications may include infection of the uterus (chorioamnionitis), which may be severe and compromise the health or the life of the mother.
B) Expectant management. This involves monitoring the mother for evidence of infection or labor and follow the pregnancy with serial ultrasound examinations. Antibiotics may be prescribed for one week. Patients are not necessarily hospitalized until they reach viability (23-24 weeks). At that time, they may be advised to be admitted to the hospital and remain hospitalized for the remainder of the pregnancy. Antenatal corticosteroids may be prescribed in anticipation of preterm delivery to hasten the maturation of the fetal lungs.
What is the "Amniopatch"?
An alternative to either of the 2 standard options mentioned above, is to perform a procedure to reseal the amniotic cavity. This procedure, invented by Dr. Quintero, is called "The Amniopatch." The principle is similar to the blood patch used to seal leakage of cerebrospinal fluid in some patients after epidural anesthesia. The amniopatch consists of the injection of healing products (platelets and cryoprecipitate) into the amniotic cavity with a thin needle under ultrasound guidance. The platelets attach to the membrane defect and seal it. The cryoprecipitate firms up the platelet clot and promotes further healing. Clinical experience with the amniopatch suggests that it may be successful in sealing the membranes in approximately 2/3 of cases of I-PROM.
What are the inclusion criteria to offer an amniopatch?
The amniopatch can be offered to patients that have had I-PPROM prior to 24 weeks and who have not undergone a vaginal ultrasound or a digital vaginal examination. Patients should not have obvious signs of intraamniotic infection (fever, uterine tenderness, foul smelling amniotic fluid, or fetal tachycardia), uterine contractions or be in labor.
Are there any complications from the amniopatch?
The injection of platelets and cryoprecipitate may result in fetal death. The sudden activation of a large amount of platelets can release substances from the platelets that can cause fetal bradycardia and fetal death. This complication can be prevented by not having a filter in the tubing where the platelets are drawn from and by limiting the amount of platelets injected. The clot formed by the platelets and cryoprecipitate may also result in bands that can encircle a fetal limb and obstruct the circulation distal to the constriction. In such cases, the fetus could be at risk of having a spontaneous amputation below the level of the constriction. This complication may not be prevented, but may be diagnosed subsequently during the pregnancy with ultrasound and treated either by delivering the baby or by releasing the constriction with endoscopic fetal surgery.
Can the amniopatch be offered to patients with spontaneous PPROM?
Patients that have spontaneous PPROM (PPROM without a prior invasive procedure) typically do not respond to treatment with an amniopatch. Therefore, it is not usually offered to these patients. Notwithstanding, Dr. Kontopoulos and Dr. Quintero have treated successfully one patient with spontaneous PPROM with an amniopatch. Further research and experience will be required to determine the merit of this treatment for patients with spontaneous PPROM.