Anomalies of the Placenta and the Cord

By: Jacqueline P. Melgazo

Anomalies of the Placenta

• The placenta and the cord are always examined for the presence of anomalies after birth. The normal placenta weighs approximately 500 g and is 15 to 20 cm in diameter and 1.5 to 3.0 cm thick. Its weight is approximately one sixth that of the fetus. A placenta may be unusually enlarged in women with diabetes.

In certain diseases, such as syphilis or erythroblastosis, the placenta may be so large that it weighs half as much as the fetus. If the uterus has scars or a septum, the placenta may be wide in diameter because it was forced to spread out to find implantation space.

Placenta Succenturiata

• A placenta succenturiata has one or more accessory lobes connected to the main placenta by blood vessels. No fetal abnormality is associated with this type. However, it is important that it be recognized, because the small lobes may be retained in the uterus after birth, leading to severe maternal hemorrhage. On inspection, the placenta appears torn at the edge, or torn blood vessels extend beyond the edge of the placenta. The remaining lobes must be removed from the uterus manually to prevent maternal hemorrhage from poor uterine contraction.

Placenta Succenturiata

Placenta Circumvallata

• Ordinarily, the chorion membrane begins at the edge of the placenta and spreads to envelop the fetus; no chorion covers the fetal side of the placenta. In placenta circumvallata, the fetal side of the placenta is covered to some extent of chorion. The umbilical cord enters the placenta at the usual midpoint, and large vessels spread out from there. They end abruptly at the point where the chorion folds back onto the surface, however. (In placenta marginata, the fold of chorion reaches just to the edge of the placenta.) Although no abnormalities are associated with this type of placenta, its presence should be noted.

Placenta Circumvallata

Battledore Placenta

• In a battledore placenta, the cord is inserted marginally rather than centrally. This anomaly is rare and has no known clinical significance.

Battledore Placenta

Velamentous Insertion of the Cord

• Velamentous insertion of the cord is a situation in which the cord, instead of entering the placenta directly, separates into small vessels that reach the placenta by spreading across a fold of amnion. This form of cord insertion is most frequently found with multiple gestation. Because it may be associated with fetal anomalies, the newborn should be examined carefully.

velamentous insertion of the cord

Vasa Previa

• In vasa previa, the umbilical vessels of a velamentous cord insertion cross the cervical os and therefore deliver before the fetus. The vessels may tear with cervical dilatation, just as a placenta previa may tear. Before inserting any instrument such as an internal fetal monitor, structures should be identified to prevent accidental tearing of a vasa previa. Tearing would result in sudden fetal blood loss. If sudden, painless bleeding occurs with the beginning of cervical dilation, vasa pervia should be suspected.

• It can be confirmed by sonography. If vasa previa is identified, the infant needs to be born by cesarean birth.

• Vasa Previa - a midwives dictionary definition is ‘Vessels in front of the presenting part. A rare condition of velamentous insertion of the umbilical cord, usually with a degree of placenta previa, in which the vessels in the membranes are lying in front of the presenting part. When the membranes rupture there is a risk of compression of, or even hemorrhage from these vessels leading to hypoxia or hemorrhage to the child.

Vasa Previa

Placenta Accreta

• Placenta accreta is an unusually deep attachment of the placenta to the uterine myometrium. The placenta will not loosen and deliver. Attempts to remove it manually may lead to extreme hemorrhage because of the deep attachment. Hysterectomy of treatment with methotrexate to destroy the still-attached tissue may be necessary (Adair et al., 2004).

Placenta Accreta

Anomalies of the Cord

Two-Vessel Cord

• A normal cord contains one vein and two arteries. The absence of one of the umbilical arteries is associated with congenital heart and kidney anomalies, because the insult that caused the loss of the vessel may have affected other mesoderm germ layer structures as well. Inspection of the cord must be made immediately at birth, before it begins to dry, because drying distorts the appearance of the vessels. Document the number of vessels present conscientiously. The child with only two vessels needs to be observed carefully for other anomalies during the newborn period.

The umbilical cord is the tube-like structure that connects the baby at the abdomen to the placenta (and mother). The umbilical cord usually contains three blood vessels ; a single vein and 2 arteries ( a 3 vessel cord) . The vein carries blood rich in oxygen and nutrients from the placenta to the fetus. The arteries carry oxygen poor blood and waste products from the fetus to the placenta.

Occasionally, one artery wastes away or fails to develop leaving only a single umbilical artery (a two vessel umbilical cord). A single umbilical artery (SUA) is seen in 0.2% to 1% of pregnancies. SUA is reported to be more common in twin pregnancies and in placentas where the umbilical cord is at the edge of the placenta.

Unusual Cord Length

• Although the length of the umbilical cord rarely varies, some abnormal lengths may occur. An unusually short umbilical cord can result in premature separation of the placenta or an abnormal fetal lie. An unusually long cord may be easily compromised because of its tendency to twist or knot. Occasionally, a cord actually forms a knot, but the natural pulsations of the blood through the vessels and the muscular vessel walls usually keep the blood flow adequate. It is not unusual for a cord to wrap once around the fetal neck (nuchal cord) but, again, with no interference to fetal circulation.

• The umbilical cord carries blood from the placenta to the developing baby and cord abnormalities can be dangerous for both the fetus and the mother. Cords have an average length of 24 inches at birth, according to Dr. Richard Naeye, author of Disorders of the Placenta, Fetus, and Neonate.

Problems With a Short Umbilical Cord

• According to the American Academy of Family Physicians approximately 6% of babies are born with a short umbilical cord. The risks to a baby with a short umbilical cord, under 12 1/2 inches in length, include having a prolonged labor, experiencing fetal distress and being smaller than the average for their gestational age. Extremely short cords seen in ultrasound may indicate a genetic problem and the doctor should follow up on this kind of observation with further genetic tests.

• Sometimes, a short umbilical cord will prevent the baby from being able to travel all the way down the birth canal because the cord acts like a rope holding the baby back. Other problems that occur with a short cord are when the cord pulls the placenta free earlier than it should during birth or the cord ruptures due to the tugging. Babies with these problems must be delivered by emergency C-section if the umbilical cord length is not discovered before the birth.

• Short umbilical cord babies are considered at high risk for having potentially fatal problems during their first year of life, so they should be monitored carefully by both their parents and their pediatrician during that first year.

Problems With a Long Umbilical Cord• Umbilical cords over 27 1/2 inches are

considered long. A long umbilical cord doesn't generally indicate any birth defects, but can be a problem if the fetus gets tangled in the cord or manages to tie it into a tight knot that prevents proper blood and nutrient flow. This kind of fetal entanglement is not uncommon and can often be treated during birth as long as the medical practitioner is aware of it beforehand.

• Some doctors and researchers believe that a long cord is a sign of a hyperactive baby, since the length of the cord normally increases with increased movement of the fetus in the womb.

• In most cases, a short umbilical cord is more worrisome than a long umbilical cord, but both conditions should be carefully watched by the doctor to ensure that any necessary medical steps, such as an emergency C-section, can be planned for well ahead of time.

References

• http://nursingcrib.com/nursing-notes-reviewer/maternal-child-health/anomalies-of-the-placenta/

• http://www.bioscience.org/atlases/fert/htm/figures/plac1.htm

• http://www.obfocus.com/high-risk/birthdefects/single%20umbilical%20artery.htm

• http://www.pnas.org/content/103/14/5478/F1.expansion.html