Velamentous cord insertion

Signs and symptoms of velamentous cord insertion during pregnancy include blood vessel compression, decrease in blood supply to the fetus, and impaired growth and development of the fetus. Blood tests taken in the second trimester may reveal increased levels of serum human chorionic gonadotropin and reduced levels of alpha-fetoprotein. The mother may also experience vaginal bleeding, particularly in the third trimester. ==Pathophysiology==

The exact mechanisms leading to insertion of the umbilical cord in the fetal membranes are unknown, although they are likely to occur in the first trimester. One theory is that velamentous cord insertion may arise from the process of placental trophotropism, which is the phenomenon where the placenta migrates towards areas which have better blood flow with advancing gestation. The placenta grows in regions with better blood supply and portions atrophy in regions of poor blood flow. This process of atrophy may result in the exposure of umbilical blood vessels, causing marginal or peripheral placental insertion to evolve to velamentous insertion over time. As the growth of the fetus is dependent on the organization, mass, and nutrient-transfer capacity of the placenta, fetal development is hence hindered in velamentous cord insertion. This can lead to fetal malformations and low birth weight. particularly when the site of velamentous cord insertion is in the lower uterine section as the extension of the uterine isthmus as pregnancy advances causes vessel elongation. This results in increased vascular resistance, which impedes nutrient transfer to the fetus. The umbilical vessels experience increased pressure and compression as they are not protected by Wharton's jelly. This can cause decreased or acute cessation of blood flow, decreased cardiac output, and pulmonary complications in the newborn. The elongated, exposed vessels in lower velamentous cord insertion cases are more readily compressed by the fetus, hence there is an even greater risk of non-reassuring fetal heart rate pattern and emergency caesarean section. The growth-restricting impacts of placental insufficiency resulting from velamentous cord insertion can also augment the effects of increased pressure to the umbilical vessels. Normally in the second half of pregnancy, one-third of fetal cardiac output is directed towards the placenta. This fraction is reduced to around one-fifth in the last few weeks of pregnancy, while the remaining umbilical blood is recirculated in the fetal body, corresponding with decreased fetal reserves of oxygen. In pregnancies with growth restriction, the fraction of fetal cardiac output distributed to the placenta decreases, further lowering fetal reserves. Damage to the umbilical cord vessels can occur when the amniotic membranes are ruptured, particularly in the case of vasa previa, potentially leading to fetal exsanguination. If the umbilical vessels are positioned such that their rupture is likely during labor, an elective operative birth at 35–36 weeks gestation may be planned, and corticosteroids may be administered in order to assist with fetal lung maturation. Overall, velamentous cord insertion doubles the risk of both preterm birth and acute caesarean section. Risk factors The following have been identified as risk factors for velamentous cord insertion: • Nulliparity • History of infertility • The use of assisted reproductive technology • Maternal smoking • Maternal asthma • Maternal obesity • Chronic hypertension • Type 1 diabetes • Gestational diabetes • Placental anomalies, including low-lying placenta, bilobed placenta, placenta with accessory lobe/s • Previous pregnancy with abnormal cord insertion • Having an umbilical cord with a single umbilical artery • Advanced maternal age ==Diagnosis==

Abdominal ultrasound can be used to visualize the insertion site of the umbilical cord. Overall, visualization is most successful in the second trimester, The umbilical cord and its insertion site may be obscured by the fetus, such as in posterior placenta or in low-lying placenta, or may be difficult to visualise due to conditions such as maternal obesity. In these cases, the use of Color Doppler ultrasound or transvaginal ultrasound can enhance the visualization of the umbilical cord, and are able to diagnose velamentous cord insertion at 18–20 weeks. ==Management==

If velamentous cord insertion is diagnosed, fetal growth is assessed every four weeks using ultrasound beginning at 28 weeks. If intrauterine growth restriction is observed, the umbilical cord is also assessed for signs of compression. Non-stress tests may be performed twice a week to ensure adequate blood flow to the fetus. Upon diagnosis of velamentous cord insertion, transvaginal ultrasound with Color Doppler may also be performed to determine whether any of the exposed vessels are within two centimeters (or five centimeters, a more common threshold recently) of the internal cervical os. If such vessels are identified, vasa previa may be present and cervical length is measured every week to determine the risk of premature rupture of membranes. The newborn may be delivered via normal vaginal labor if there are no signs of fetal distress. Fetal heart rate is continuously monitored for slow or abnormal heart rate patterns which may indicate fetal distress during labor. If the exposed blood vessels are near the cervix or are at risk of rupturing, the newborn may be delivered via caesarean section as early as 35 weeks gestation. ==Complications==

Maternal • Vasa previa • Small placenta • Low arterial cord pH • Intrapartum bleeding curettage, • Abnormal heart rate patterns • Low Apgar score • Fetal malformations • Fetal bleeding • Death and selective fetal growth restriction. These complications particularly arise in the case of monochorionic twins, where identical twins share the same placenta. ==Epidemiology==

Velamentous cord insertion occurs in between 0.1%-1.8% of all pregnancies, and is eight to ten times more frequent in multiple pregnancies. It is thought that sex may be a determinant of abnormal cord insertions, however there is conflicting evidence as to whether male or female fetuses are linked to greater risk of velamentous cord insertion. ==References==