~Teachingcenter的醫學筆記~

 Placenta Grading (胎盤的分級) 
Grade 0
  -Late 1st trimester-early 2nd trimester
  -Uniform moderate echogenicity
  -Smooth chorionic plate without indentations
Grade 1
  -Mid 2nd trimester –early 3rd trimester (~18-29 wks)
  -Subtle (thin) indentations of chorionic plate.
  -Small, diffuse calcifications (hyperechoic) randomly dispersed in placenta
Grade 2
  -Late 3rd trimester (~30 wks to delivery)
  -Larger indentations along chorionic plate
  -Larger calcifications in a “dot-dash” configuration along the basilar plate
Grade 3 (grade 3的胎盤容易在催生的時候FHB下降)
  -39 wks – post dates
  -Complete indentations of chorionic plate through to the basilar plate creating “cotyledons (子葉)” (portions of placenta separated by the indentations)
  -More irregular calcifications with significant shadowing
  -Placental dysmaturity which can cause IUGR (Intrauterine growth restriction)
  -Associated with smoking, chronic hypertension, SLE, diabetes

 Shape of Placenta (胎盤的形狀) 
Succenturiate placenta (副胎盤, 出現兩個一大一小的胎盤)，常見於PPH、subinvolution、uterine sepsis、uterine polyp的病人上。
Bilobed Placenta (兩個一樣大小的胎盤)，常見於Implantation over leiomyomas、Area of previous surgeries、In the cornu、Over the cervical os的病人上。
Circumvallate placenta (環繞圓盤狀胎盤)，常見於Miscarriage、Antepartum hemorrhage、Preterm delivery、Fetal growth restriction的病人上。
Placenta Membranacea (膜狀胎盤)，常見於previa (前置性胎盤) or accreta (植入性胎盤)的病人上。
Placenta Fenestrata (窗形胎盤，就是中間破了一個洞)，常見於胎盤滯留(retained placenta，胎盤沒有生乾淨)的病人上，More often the defect involves the villous tissue & the chorionic plate remains intact.
※Infarction，胎盤部分缺血性變化可能不影響胎兒和母體，約有25% term pregnancies可以看到placental infarct，一塊白白的區域，其中2/3可能和hypertension有關，原因一般是occlusion of maternal vascular supply.

 Weight of Placenta (胎盤的重量) 
一般是500~600g，東方人如果媽媽體型嬌小，有時可以容許在450g以上，胎盤過小通常合併有chronic hypertension，胎盤過大會有fetal hydrops (胎兒水腫)。

 Cord Insertion (臍帶連接的位置) 
Battledore Placenta (羽毛球拍形，連接在胎盤邊緣上)，常見於monochorionic twin pregnancy、intrauterine growth retardation、pre-term birth、low-weight at birth的病人上。
Placenta Velamentosa (帆狀，臍帶感覺沒有連在胎盤上，只有大量細小的血管連在胎盤邊緣)，通常會流掉，Incidence: 1.1% in singleton pregnancies, 8.7% in twin gestations; spontaneous abortion: 33% between 9th & 12th wks, 26 % between 13th & 16^th.

Abnormalities of umbilical cord (臍帶異常)
  -長度：正常為50~60公分，過長容易entanglement (繞頸或其他地方)、cord prolapse (脫垂)，常見於fetal distress or demise的病人上；過短容易造成abruptio placenta (早期剝離)或uterine inversion (子宮外翻)，可能造成intrapartum fetal death (2倍以上的風險)常見於IUGR、oligohydramnios、chromosomal aberration的病人上。
  -直徑：正常為1~2公分，太小可能和IUGR有關，太大可能和macrosomia有關。
  -捲繞(coiling)：胎兒在子宮內旋轉時把臍帶扭成麻花狀，正常大概5公分一轉，也就是UCI (umbilical cord index) = 0.2，若超過這個數字，就算是hypercoiling，可能造成fetal demise、IUGR、intraparum hypoxia，成因可能為trisomies或single umbilical artery；若遠低於這個數字，可能是hypocoiling，可能和meconium staining、fetal distress、preterm birth有關。
※Umbilical cord coiling index，每一公分的臍帶轉了幾圈，it is defined as number of coils per one centimeter of length of the cord.
※Single umbilical artery，正常的臍帶內血管是2動1靜，如果只有一條動脈，就是異常，incidence: 0.63 % in live births, 1.92 % in perinatal deaths, 3 % in twins. 可能和Diabetes、Epilepsy、antepartum hemorrhage、oligohydramnios、hydramnios (羊水過多過少都會)、Chromosomal abnormalities有關。

※Placenta previa之後如果placenta abruption，病人會有疼痛感