A study of stillbirth

26 Jan

Below is a rough draft of a study idea that I had hoped would make real progress on understanding the causes of stillbirth. It addresses only those deaths due to asphyxia, but from my autopsy experience this is likely to be a large number of deaths. The proposal is somewhat under-referenced, but the pages I have been adding to this site will address the appropriate literature review. I can not realistically undertake this project, but I hope the ideas might at least be useful to others interested in the topic.

Aims:

  1. To demonstrate the mechanism of asphyxia in stillbirth by investigating the intrauterine ultrasound and the maternal history in detail at the time of discovery of the intrauterine death.
  2. To correlate the above findings with the autopsy and placental examination in light of the above clinical investigation
  3. To use the information from aims 1 and 2 to develop hypotheses for potential prevention of stillbirth

 

Background:

 

There remains a group of stillborn infants that even a careful clinical, autopsy, and placental investigation fails to find the cause. This is particularly frustrating in appropriate for gestation infants without malformations, genetic disease, fetal hydrops, or infection. For analysis, this group of cases can be separated from infants born prior to extra-uterine viability in which prevention of stillbirth would be achieved by preventing very early preterm labor. The autopsy of these unexplained stillborn infants often shows evidence of the mechanism of death that is consistent with either very acute asphyxia or rapid onset of heart failure presumably from hypoxia/acidosis (see below).

The evidence of acute asphyxia is the finding of intrathoracic petechiae, much like those found in SIDS. These petechiae can be formed experimentally by tracheal occlusion at end expiration, and this is likely the mechanism in SIDS in that the infant exhales and then initiation of inhalation is blocked by a physical object. In utero, asphyxia is the stimulus to start respiration and occlusion may be a glottic stop mechanism such as that proposed to assist the first attempt of ventilation after birth. Intrathoracic petechiae are found with large placental abruption, an anatomically observable mechanism of total or near total acute asphyxia documented by placental examination(1). From experience they are present in other cases with a clear mechanism of relatively rapid asphyxia such as umbilical cord hematoma. Acute birth asphyxia as demonstrated by Dawes(2) and others results in fetal gasping that if the airway were occluded would produce negative intrathoracic pressure that could expand surface capillaries and result in their rupture. In our preliminary data such petechiae are present in 15% of all stillbirths greater than 23 weeks of gestation.

In the same study of abruption, placental separations that were small but still lethal demonstrated modest pleural and pericardial effusions, and dilated cardiac chambers in the infant. I hypothesized that this was due to acute heart failure from hypoxia leading to a positive feedback loop of hypoxia decreasing cardiac output, which decreases oxygenation, which decreases cardiac output further. In general more chronic causes of fetal hydrops produce more prominent edema, and lung hypoplasia. Like intrathoracic petechiae this pattern is also present in stillbirths without abruption, some with explained asphyxia and some with no anatomic cause. This pattern appears to be more common in small for gestation infants especially those with fixed anatomic loss of placental functional volume.

The unexplained stillborn autopsies with evidence of asphyxia producing either gasping or heart failure likely have an anatomic cause. Many potential mechanisms would be very difficult to detect by examination of the placenta or infant after delivery. For example we demonstrated in vitro that if wrapping of the cord leaves only a short free segment, flow in the umbilical vein can be stopped by modest torsion of the cord(3). In vivo this would correspond to a cord wrapping that resulted in a short segment between the umbilical insertion and the beginning of the wrapping. Aside from twisting, direct stretching of the helical structure of the cord might also interfere with blood flow in the short segment. In other cases, the position of the cord in relation to the presenting part and pelvis might lead to cord compression from occult prolapse or undetected funis previa. Oligohydramnios may favor the cord being trapped, and this would not be detectable after delivery. Other anatomically “invisible” factors such as maternal ketosis, hypoxia, sleep apnea, decreased uterine flow for example from venal caval compression with supine position could be contributing factors to fetal hypoxia. Some of the factors may be detectable by directed ultrasound at the time of fetal death, while others may be detectable by a detailed and open-ended maternal history and examination.

Our goal is to not use a risk factor approach, but rather a deductive approach to solve the cause of death in the individual infant. Obesity is a risk factor for stillbirth(4), but we want to discover the mechanism of death of a particular infant in that obese mother. The hope is that some of those mechanisms may be detectable and preventable without the difficulty of reducing the overall risk factor, for example obesity. Our approach will be sensitive and reassuring to the parents’ anxiety and guilt, and will attempt to secure their involvement in the process of discovering the unknown mechanisms of stillbirth. Our approach also involves a detailed cooperation of clinician and pathologist in a mutually informing interaction in interpreting all of the findings in individual cases, and then pooling the information. This study would obtain detailed information on traditionally known and unknown causes of stillbirth.

 

Methods:

 

Any pregnancy with intrauterine fetal death is eligible to be enrolled in the study. The triggering event is the detection of the death, and immediate notification of a study member on call to request consent and begin the process. The first step after consent is a detailed ultrasound noting fetal position, amount of amniotic fluid, any structural details of the placenta, the distance of free umbilical cord from the placental insertion if that can be measured, and inspection of areas around the fetal presenting part in the pelvis for evidence of umbilical cord compression. A discussion with the parents is initially open ended as to events in the previous week, day, hours with directed questions about fetal movement, use of medications, trauma, with the approach of encouraging the parents to talk about their own concerns, and to record this information. We will speak with parents separately and together. A normal routine review of systems by history and exam, and review of the prenatal record and prenatal tests and ultrasound would be included. The physical exam would include cervical dilatation, maternal weight and height compared to pre-pregnancy, and vital signs. Maternal blood would be drawn for possible infection titers, K-B, and saved serum for potential markers and DNA. A EDTA tube would be drawn for possible coagulation markers. The goal is to obtain the specimen but the testing would be determined on algorithms based on history, and findings in the placenta and the fetal autopsy. The consent would include permission for placental examination. The autopsy consent would follow the normal procedures including the extent of the autopsy, and the disposition of the infant. To the extent possible, the obstetrician and other clinical caretakers of the infant will be included in all the consent process as additional resources for the patient’s questions. If the membranes have not ruptures amniotic fluid will be obtained.

The examination of the placenta starts with measuring the entire cord length on the infant and on the placenta. The cord and placenta are photographed with fetal and maternal surface, and two longitudinal photographs of the cord. A standard pathology protocol would be followed that records umbilical cord: vessel number, insertions, color, average diameter, and lesions. Membranes: color, rupture, and lesions. Fetal surface: margin, color, vessels, lesions, Maternal surface: completeness, lesions and cut sections at 1 cm intervals but also cuts of all palpable lesions. The cute sections are also photographed. Routine sections are taken (ends and middle of the umbilical cord, rupture edge to margin of the fetal membranes, and at least 3 sections of the placenta including one through the umbilical cord insertion, as well as sections of lesions as needed). A sample of fresh rinsed placental villi and cord will be frozen for storage as well.

The stillborn autopsy will also follow a specific protocol. The external examination will include the usual measures and body weight. The examination will include the physical portion of the Ballard score to estimate gestation with documenting photographs. The photographs will also be taken to document the extent of skin slippage, fetal hemoglobin staining of the cord and sclera, and the fullness of the fetal skull. A radiograph will be taken AP and lateral if possible with a Faxitron or fine resolution to detect opacities in the fetal liver and bowel. The internal examination will include a window in the chest to measure and obtain pleural fluid volume and sample, a lung culture, and a photograph of the anterior thoracic cavity before dissection and again after removal of the entire thymus and pericardium. A separate photograph will be made of the ductus arteriosus in situ after removing the vagal bundle for visibility and retracting the left lung. A photograph of the abdomen in situ will also be made to judge the liver size, color and the color of the colon. A routine autopsy and sampling will be done by protocol adaptable to the findings as well as those of the history and placental findings. A portion of fetal liver and brain will be frozen. The routine heart examination in a fetus usually follows the dissection along the lines of blood flow. If the heart appears externally normal based on a systematic examination e.g. symmetry of the great vessels, symmetry of the ventricle, location of the great vessels and pulmonary veins, etc ) then the heart will be fixed and cut in cross section in the coronal plane of the posterior atrio-ventricular junction at 3 mm intervals and photographed and measured to determine dilatation. Sections will be made to include the tips of the papillary muscles to look for myocardial necrosis.

One aim of the placental and autopsy examination is to develop the most useful protocol for evaluating the mechanism of stillbirth. The baseline protocols recognize the value of current practice, but add some additional information, and are designed to retain photographic and physical materials for reevaluation. The baseline information obtained will be entered into a Filemaker Pro database that allows for easy modification, multiple screens for different types of information.

The process is one of collaboration and critical review, and ongoing modification. Each autopsy is reviewed within in the institution and at least one of the co-PI in both pathology and obstetrics and a critique produced. The findings are presented to the parent(s) in a conference. The parent’s questions and further information are also entered as data. All of the cases are reviewed monthly from the Filemaker database to monitor the success of collection of data, to identify potential improvements. Annually, all the cases are reviewed by all co-PI’s and ideas are presented at an annual meeting.

Hypothetical examples of the conference: If there is evidence that unusual physical exertion or weight loss, or gastrointestinal illness preceded stillbirth in obese patients, does the autopsy confirm fetal heart failure possible related to ketosis. Is there published information on models of this effect? Are there experts in this area that we can consult? Can we quantify myocardial glycogen in the infant, and do we know the effect of intrauterine postmortem retention time on those levels. Do we need to freeze a myocardial sample on cases for either frozen section PAS stain or direct assay of glycogen levels. How many cases that might relate to this cause are likely to occur annually. Are there better ways to evaluate maternal blood or urine? Should we collect a urine sample on obese mothers in the study? How important is underlying maternal glucose intolerance? Should we also test HA1c in these cases? How many more stillbirths would be needed to recruit to test the hypothesis of ketosis as a mechanism of death. The uniqueness of this process is that the direction of the study cannot be anticipated since it develops from the data being acquired. It may be that obsese patients have increased stillbirth because of pelvic narrowing from internal adipose with increased chance of umbilical cord entrapment against the presenting part, an insight that would trigger an entirely different approach to further the research into mechanism, risk and prevention.

The same approach would be applied to known mechanisms of death such as placental abruption. In those cases, even with known risk factors such as preeclampsia, cocaine, or thrombophilia, there may be common historical factors such as prolonged supine position or physical deceleration that might turn a potential into an actual retroplacental hematoma, or there may be better predictors such as other small retroplacental or retromembrane hematomas in context with the other risk factor. Even if there are no indirect clues, more systematic evaluation of the fine structure of the retroplacental hematoma microscopically might pin point the area of initiation and growth of the separation to better understand dynamics and possibly the timing. The question to be answered is why did this particular patient have an abruption and can that provide a more general insight in understanding the mechanism and preventing it

The only inclusion criterion is a prenatally detected stillbirth. Ideally recruiting a core of four or five institutions with more than 10,000 deliveries per year should provide 80 to 100 cases per year for inclusion. Part of the goal of this methodology is to have a core of committed people becoming increasing knowledgeable about stillbirth. Each institution would have two main Co-PIs one in maternal fetal medicine or obstetrics, and one in pathology, and care-giver teams.

There is no statistical analysis for this study. The approach is unconventional, and the outcome is the production of new testable hypotheses and creation of a core of experienced researchers in this area. There is also an expectation that the hypothesis about stillbirth will also have bearing on prepartum and intrapartum asphyxia that can cause neurologic injury to the infant.

 

References:

 

  1. Bendon RW. Review of autopsies of stillborn infants with retroplacental hematoma or hemorrhage. Pediatr Dev Pathol. 2011;14(1):10-5.
  2. Dawes G. Foetal and Neonatal Physiology. Chicago, IL: Year Book Medical Publishers, Inc.; 1968. 247 p.
  3. Bendon RW, Brown SP, Ross MG. In vitro umbilical cord wrapping and torsion: possible cause of umbilical blood flow occlusion. J Matern Fetal Neonatal Med. 2014;27(14):1462-4.
  4. Yao R, Ananth CV, Park BY, Pereira L, Plante LA, Perinatal Research C. Obesity and the risk of stillbirth: a population-based cohort study. Am J Obstet Gynecol. 2014;210(5):457 e1-9.

 

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