Patient's question:
Observations: Fetal growth indicators: Biparietal diameter 38mm, Head circumference 148mm, Abdominal circumference 144mm, Femur length 26mm. Fetal head position: Above the symphysis. Fetal lie: LOA (Left Occiput Anteroposterior). Fetal presenting part: Head presentation. Skull，。 Fetal heart: No abnormality in the heart axis, Four-chamber heart structure displayed. M-mode ultrasound shows: Heart rate 161 beats per minute, Regular rhythm. Two umbilical arteries, No umbilical cord. Stomach bubble displayed, Both kidneys displayed, Bladder displayed. Placenta located on the posterior wall of the uterus, Fetal heart rate: 161 times/min, Placental maturity: Grade I. Thickness/mm Amniotic fluid dark area: 43mm, Index:/mm. Other: PlacentaDoctor's answer:
A velamentous placenta refers to a condition where the umbilical cord attaches to the fetal membrane, with vessels spreading fan-like through the membrane to reach the placenta. This type of placenta is rarer, occurring in about 10% of cases compared to a discoid placenta. The incidence in twins is nine times higher than in single births, and DeLee (1938) noted that it nearly always appears in triplets. This condition poses no danger to the mother but results in a fetal mortality rate of 60–80%. If the cord attachment point is near the lower margin of the placenta close to the cervix, it may be compressed by the presenting part of the fetus, leading to fetal distress and even death. When the vessels are close to the cervix and located anterior to the presenting part (known as vasa previa), they can cause severe bleeding due to the rupture of the membranes and tearing of the vessels. Diagnosing vasa previa is challenging. Before membrane rupture, if pulsating vessels are palpated through the dilated cervix at the presenting part, the diagnosis can be made. After membrane rupture, painless vaginal bleeding occurs, and clinical examination reveals no signs of early placental separation, placenta previa, or other bleeding causes, while the fetal heart rate becomes irregular or slows. In such cases, further tests should be conducted to determine if the vaginal bleeding is fetal blood. The methods include: ① Vaginal blood smear: The presence of nucleated red blood cells indicates fetal bleeding; ② Siger's alkaline test: If the blood is fetal hemoglobin, it turns pink; maternal hemoglobin turns yellow; ③ Klehauer test: Blood smears are incubated in acidic pH and examined; maternal blood cells dissolve, while fetal blood cells do not. If the vaginal bleeding is confirmed to be fetal blood, combined with the medical history, the diagnosis can be confirmed. Postpartum placental examination may reveal the umbilical cord attached to the fetal membrane at the edge of the placenta.【Differential Diagnosis】
Velamentous placenta is similar to a discoid placenta, as both have the umbilical cord attached to the placental margin, but in a velamentous placenta, the cord attaches to the fetal membrane rather than the placenta itself.