By Steven G. Gabbe, MD
In 1904, ballantyne said, "a diseased foetus without its placenta is an imperfect specimen, and a description of a foetal malady, unless accompanied by a notice of the placental condition, is incomplete."1 Today, the placenta is a forgotten organ. Most presentations at case conferences and at the Labor and Delivery board, while describing the fetal heart rate tracing in detail and providing information about the condition of the newborn, rarely comment on the appearance of the placenta. Yet, the information learned from a systematic placental examination in the delivery room may be important in understanding the outcome of the present pregnancy, can be of value when counseling the patient and her partner about the outcome of future pregnancies, and may yield critical information in the event of malpractice litigation. This article describes how to conduct an examination of the placenta, those features that have important implications for perinatal outcome, and identify those pregnancies in which placental examination by a pathologist should be considered.
Placental evaluation can begin during the antepartum period using ultrasound. The obstetrician might identify a subchorionic hematoma, a two-vessel umbilical cord, an area of placental abruption, or a multiple gestation. Such findings certainly warrant careful examination of the placenta at delivery.
The College of American Pathologists has recommended that the obstetrician assume the responsibility for examination of the placenta in the delivery room with triage of those placentas requiring more detailed examination to the pathologist. If this process is followed, it has been estimated that only 10-15% of placentas would require pathological examination, including microscopic sections.2 Given the cost of a placental examination by a pathologist ($200-$250) this approach would seem to be practical and cost-effective.
What should be included in a gross examination of a placenta?2 The clinician should measure the umbilical cord and determine whether a cut cross-section reveals the normal three vessels. A single umbilical artery, observed in 0.5-1.0% of pregnancies, has been associated with a 20% risk of major fetal malformations and with trisomy 18. The normal umbilical cord is 30-70 cm at term. An abnormally long cord may contribute to cord knots, fetal entrapment, and cord prolapse. A short umbilical cord indicates decreased fetal movement and may be associated with fetal malformations including neuromuscular abnormalities of the fetus. The membranes should be carefully inspected and the site of membrane rupture identified. Cloudy or opaque membranes may be a sign of infection, while green discoloration indicates meconium staining. The site of the insertion of the umbilical cord should be assessed. Velamentous insertion of the cord or vessels running through the membranes increase the risk of disruption of cord vessels and fetal bleeding. The insertion site of the chorioamniotic membranes should be examined, and the chorion and amnion should be separated to examine the color and consistency of each. Should infection be suspected, it is best to culture between the membranes. Amnion nodosum, small nodules of compressed hair and squames on the amniotic surface, suggest oligohydramnios and are often seen in cases of renal agenesis. After trimming off the membranes and cord, the placenta can be weighed. At term, the fetus should weigh approximately seven times more than its placenta.
In the case of a multiple gestation, the umbilical cords should be identified at delivery according to birth order. The number of placental masses should be recorded and the dividing membranes examined. When monozygotic placentation is suspected, particularly in cases of twin- twin transfusion syndrome, the pathologist may use vascular injections to identify these anastomoses. Since they contain only the two amnions, monochorionic dividing membranes are usually thin and transparent. In contrast, dichorionic dividing membranes with two amnions and two chorions are more opaque.
The maternal surface of the placenta should be examined to be sure that it is complete and measurements are made of its two largest diameters and width. Examination of the maternal surface may reveal adherent blood clots suggestive of an abruption. The size of the clots should be estimated, and the presence of placental infarcts should be noted. Recent infarcts may be dark and red, while older infarcts are tan or white. Up to 10% of normal placentas may have small marginal infarcts measuring less than 1 cm.3 Chorioangiomas, the most common placental tumors, represent fetal capillary hemangiomas. They are generally well circumscribed and dark red in color. When larger than 5 cm, chorioangiomas function as a low-resistance shunt and may lead to fetal cardiac failure and hydramnios.
Indications for Placental Examination
Systemic disorders such as:
Diabetes mellitus, hypertension, and collagen vascular disease
History of reproductive failure
History of substance abuse
Severe maternal trauma
Invasive procedures such as cord blood sampling and fetal shunt placement
Unexplained third-trimester bleeding
Stillbirth or neonatal death
Admission to neonatal intensive care unit
Compromised neonatal condition at birth
Intrauterine growth restriction
Major congenital malformations
Gross abnormality on triage examination
Having carefully examined the placenta in the delivery room, which placentas should be sent for further pathological examination? It has been suggested that all placentas undergo microscopic examination or that a block of tissue be obtained from all placentas and stored.4 This practice has not been recommended by the College of American Pathologists5 or the American College of Obstetricians and Gynecologists.6 One alternative that may be considered is storing the fresh placenta in a plastic bag at 4°C for at least three days until the course of the newborn has been observed.5 However, if indicated, many tests, such as bacterial and viral cultures and samples for cytogenetics studies and specific metabolic abnormalities, must be obtained from the placenta when it is fresh. When requesting a detailed placental examination, it is essential that the obstetrician provide the pathologist with the patient’s antepartum and intrapartum obstetrical history, information about the condition of the newborn, findings from the triage examination of the placenta, and the questions the obstetrician hopes to have answered by the placental examination. The indications for placental examinations may be divided into maternal, perinatal, and placental. (See Table.) These guidelines are used at the University of Washington Medical Center and are based on the recommendations of the College of American Pathologists.5
Finally, it is essential that information from the examination of the placenta be shared with all of the patient’s health care providers. We have found that a conference including obstetricians, maternal fetal medicine specialists, pediatricians, neonatologists, obstetrical anesthesiologists, pathologists, and nurses provides an ideal forum for these discussions. The obstetrician can then meet with the patient and her partner to share this collective wisdom.
1. Ballantyne JE. Manual of Antenatal Pathology and Hygiene: The Embryo. Edinburgh, Scotland: Green; 1904.
2. Driscoll SG. Placental examination in a clinical setting. Arch Pathol Lab Med 1991;115:668-671.
3. Kaplan C, et al. College of American Pathologists, Conference XIX on the examination of the placenta: Report of the working group on the definition of structural changes associated with abnormal function in the maternal/fetal/placental unit in the second and third trimesters. Arch Pathol Lab Med 1991;115:709- 716.
4. Salafia CM, Vintzileos AM. Why all placentas should be examined by a pathologist in 1990. Am J Obstet Gynecol 1990;163:1282-1293.
5. Altshuler G, Deppisch LM. College of American Pathologists Conference XIX on the examination of the placenta: Report of the working group on indications for placental examination. Arch Pathol Lab Med 1991;115:701-703.
6. College of American Pathologists Conference XIX. The examination of the placenta: Patient care and risk management. Arch Pathol Lab Med 1991;115:641-732.