It was many years ago. A mother-to-be at 38 weeks of gestation had vaginal bleeding, a rapid decrease in fetal heart rate and abnormal fetal heart monitoring, and despite an emergency cesarean section, she was unable to save the life of her fetus. I believe that many obstetricians often encounter that many pregnant women are found to have placental abnormalities only after safe and smooth delivery when the doctor examines the placenta, and most of them are in a cold sweat at that time. Due to the cases that happened around us and the widespread spread of self-published media, many mothers-to-be are afraid of talking about “sail-shaped placenta”! If you type in “placenta praevia” in Baidu, you will find more than 379,000 results, including professional papers, forum postings, and urgent inquiries and questions from mothers-to-be. The incidence of placenta praevia is increasing with the influence of social and environmental factors, but at the same time, obstetricians and ultrasonographers have become more aware of the disease, so if the placenta praevia is detected and diagnosed in time before delivery, and if monitoring is actively enhanced, timely or elective cesarean section is chosen to terminate the pregnancy, the fetal mortality rate due to placenta praevia can be effectively reduced. What is placenta praevia? As the name implies, its named after the shape of a sailboat. Before explaining the condition, let’s understand the normal placenta and umbilical cord and the relationship between the two attachments, which will help to deepen the understanding of sail placenta. The placenta is a very complex and delicate system of vascular network through which maternal blood as well as fetal blood completes the process of material exchange. Through this system, the mother provides nutrients and oxygen to the fetus, while carrying away metabolites and carbon dioxide from the fetal blood. In addition, the normal fetal umbilical cord has three blood vessels, one vein and two arteries, which are arranged in a zigzag pattern. There is a very important substance between and around the three blood vessels, which is called Huatong gum. Normally, the umbilical cord is attached to the placenta either medially or paracentrally, in about 90% of cases. The difference between sail-shaped placenta and normal placenta is that the umbilical cord is not attached to the placenta, but to the fetal membrane outside the placenta, then the vessels of the umbilical cord are scattered into several branches in a fan-shaped distribution, and these branches are finally connected to the edge of the placenta. The placenta is called sail-like. Because of the loss of the normal umbilical cord structure around these vascular branches and the lack of the support of Huatong glue, vascular rupture can easily occur, especially when these vascular branches are located below the fetal previa (the first part of the fetus to enter the pelvic inlet during delivery), crossing or close to the inner cervical opening, when the vascular pressure or the rupture of the fetal membrane, the vascular tear can cause fetal hypoxia or acute blood loss, which is medically called vascular previa. This kind of hemorrhage is fetal hemorrhage. Since the blood volume in a full-term fetus is about 250 ml, fetal hemorrhagic shock can occur if the blood loss exceeds 20-25% (50-60 ml), and therefore the fetal mortality rate is extremely high. Sail placenta is a rare placental cord anomaly first reported in 1773 by Wrisberg in Germany. The incidence of the disease ranges from 0.24% to 1.80% in singleton pregnancies, up to 9% in twin pregnancies, and more often in triplets and above. So how does sail placenta form? Are there any risk factors that can easily induce the development of placenta praevia? Unfortunately, although modern medical science continues to mature, the etiology of placenta praevia is still an open question for us. However, most medical experts agree with the “dystrophic” theory, which suggests that the umbilical cord is attached to the placenta in a normal position during early embryonic development, but later, due to endometrial dysplasia or endometritis in the original placental area, the placenta will grow in the direction of rich blood supply, thus making the cord gradually become eccentric to the edge, or even The cord becomes eccentric to the edge or even free from the placenta. In addition, studies have pointed out that placenta praevia (placenta in low position or covering the inner cervical opening), bilobed or multi-lobed placenta, parietal placenta and other placental abnormalities, twins and multiple births are risk factors for the occurrence of sail placenta. Clinical practice has also found that advanced maternal age, especially women with a history of cesarean delivery and multiple miscarriages, are more likely to result in sailor placenta, probably due to the single or multiple synergistic effects of the above factors that damage the endometrium and easily lead to insufficient blood supply to the placental area. In cases of placenta praevia, painless vaginal bleeding of a small amount, bright red in color and a sharp drop in fetal heart rate may occur in late pregnancy or immediately after rupture of membranes, indicating rupture or compression of the anterior vessels, directly indicating that the fetus is in extreme danger. However, the sail placenta is not always so terrible, if the umbilical cord vessels are located above the fetal previa, there is basically no obvious adverse effect on the fetus. In summary, one may ask, is there a particularly effective test to correctly diagnose placenta praevia before delivery, so that a cesarean section can be performed selectively before the membranes rupture, thus reducing fetal mortality? Unfortunately, there is no specific method of diagnosis. In the case of sail placenta, especially vascular placenta, painless vaginal bleeding occurs late in pregnancy or immediately after rupture of membranes and is often misdiagnosed as placenta praevia, placenta abruptio, or redness. However, vaginal bleeding in sail placenta comes from the fetus, whereas in the latter three vaginal bleeding comes from the mother. There are a number of laboratory tests available to determine if the vaginal bleeding is from the fetus or the mother. The Ogita test is generally used clinically and is simple to perform and short in duration. A smear of a fresh vaginal blood specimen is taken and if nucleated red blood cells or juvenile red blood cells are found, the diagnosis can be made because if the pregnant woman does not have an associated blood disorder, the cells are of fetal origin only. A pre-prepared solution is added to the blood specimen after 2 minutes of shaking with an alkaline solution. A drop of the mixture is taken on a filter paper and observed after 30 seconds; in the case of alkaline-resistant fetal hemoglobin, a colored circle may form around it. This method can be used to make a quick diagnosis for small amounts of vaginal bleeding, but it is often not helpful when there is a lot of bleeding, as the disease progresses quickly. In addition, if a pregnant woman is in full-term spontaneous labor and requires manual rupture of the membranes, the physician often needs to examine vaginally, and if there is a sail placenta vasoprevia, the finger can palpate a fixed vascular pulsation in the amniotic membrane at the same frequency as the fetal heart rate. The use of amnioscopy has been suggested, and although the results are more reliable, its invasive nature, cost and high technical content make it difficult to perform universally. However, there is another common and easy method to detect and diagnose sail placenta in clinical practice, which is color ultrasound Doppler technique. With the continuous development and wide application of ultrasound technology and the improvement of ultrasonographers’ knowledge of sail placenta, the detection rate of prenatal sail placenta has increased year by year. Ultrasonography can observe the type and position of the placenta, the part of the umbilical cord attached to the placenta, and in some pregnant women who need transvaginal ultrasonography, it can also show more clearly the structure in and around the inner cervical opening and the course of the anterior vessels on the fetal membrane. It has been found that prenatal ultrasound with purposeful observation of the placental cord attachment site can improve the display rate of the sail placenta, with a diagnostic accuracy rate of 91%. However, there are many factors that affect ultrasound as an effective examination modality, such as too large or too small a gestational week, too little amniotic fluid, placenta located on the posterior wall, and interference with fetal position, thus reducing the correct rate of examination. In the literature, it is advisable to perform systematic fetal ultrasound screening between 16 and 28 weeks of gestation, focusing on the placental cord attachment point. According to some domestic obstetricians, the best time to diagnose sail placenta is before 28 weeks of gestation for singleton and 20 weeks of gestation for twin fetuses, and the diagnostic compliance rate is 97.7%. Although the attachment point of the umbilical cord placenta can be clearly shown at 11-14 weeks of gestation, with the increase of gestational weeks, the placenta is displaced due to the enlargement of the uterus, and some of the early pregnancies show normal placenta umbilical cord position structure, but it may progress to sail-like placenta in middle pregnancy. In late pregnancy, due to the influence of amniotic volume, fetal and placental position, especially in posterior placenta, many placental cord attachment points are not clearly shown, and it is easy to miss the diagnosis. If no obvious signs of fetal hypoxia or maternal complications are found, elective cesarean section can be waited until after 37 weeks of gestation. If a pregnant woman is at risk of preterm labor, she should be hospitalized at 30 to 32 weeks of gestation for observation and promptly terminate the pregnancy by cesarean section if abnormal fetal heart monitoring or fetal distress occurs. If the diagnosis is not confirmed before delivery and vaginal bleeding with fetal heart changes occurs in late pregnancy or during delivery, after excluding placenta praevia, placenta abruptio, redness, etc., there should be a high suspicion of ruptured placenta with anterior vessels, and the source of bleeding should be determined in time, and measures should be taken to end the delivery quickly. In conclusion, we need to be worried about the placenta sailing, but if we have the ability to “know our enemy”, in fact, the placenta sailing is not terrible. Due to the objective limitations of the examination technology, timely and effective communication between doctors and mothers-to-be is needed to detect the signs of placenta praevia in time to prevent it from happening and minimize the risk!