Medical brain notes 42

  Third-Trimester Bleeding Approximately 4% to 5% of pregnancies are com   plicated by vaginal bleeding in the third trimester.   Bleeding ranges from spotting to life-threatening hemorrhage. Intercourse and recent pelvic examinations are common precipitants of spotting, as the cervix is more vascular and friable in pregnancy. Twenty percent of car-diac output is shunted to the pregnant uterus, so significant bleeding can be quickly catastrophic. Severe hemorrhage is much less common than spotting, but remains a leading cause of maternal and fetal morbidity and mortality.  Thetwo most common causes of significant bleeding are placenta previa (in which the placenta is located close to or over the cervical os) and placental abruption (premature separation of the placenta).  Other important causes of bleeding are preterm cervical change, preterm labor, and uterine rupture. In many cases, bleeding remains unexplained or is attributed to local lesions. Possible cause...

  PLACENTA PREVIA   Placenta previa  is a placental location close to or over the inter-nal cervical os.  It can be classified as complete, in which theplacenta completely covers the internal os, or  partial,  in which the placenta overlies part but not all of the internal os. A placenta that extends into the lower uterine segment but does not reach the internal os is called a  low-lyingplacenta.  (Fig. 21.1.) Placenta previa classically presents with painless bleeding in the third trimester   In many cases there may be small amounts of bleeding prior to a more significant episode of bleeding. About 75% of women with placenta previa will have at least one episode of bleeding. On average this episode occurs at around 29 to 30 weeks of gestation. In general, placenta previa occurs in about 1 in 200 pregnancies. The incidence of placenta pre-via earlier in pregnancy (approximately 24 weeks) is 4% to 5% and decreases with increasing gestational a...

  PLACENTAL ABRUPTION   Placental abruption  refers to an abnormal premature separa-tion of an otherwise normally implanted placenta.  There arevarious types of abruption, depending upon the extent and region of separation. A  complete abruption  occurs when the entire placenta separates. A  partial abruption  exists when part of the placenta separates from the uterine wall.   Marginal abruption  occurs when the separation is lim-ited to the edge of the placenta (Fig. 21.3). A significant abruption requiring delivery occurs in 1% of births. Abruption occurs when bleeding in the decidua basalis causes separation of the placenta and further bleeding. The classic presentation of abruption is vaginal bleeding with abdominal pain. Smaller or marginal abruptions may pre-sent with bleeding only.  Concealed hemorrhage  occurs when blood is trapped behind the placenta and is unable to exit. Painful uterine contractions, significant feta...

  VASA PREVIA   Vasa previa  describes the passage of fetal blood vessels overthe internal os below the presenting part of the fetus.  It canoccur with a  velamentous insertion,  in which the fetal blood vessels insert into the membranes between the amnion and chorion instead of into the placenta and are not protected by Wharton jelly (Fig. 21.4), or when there is a succenturiate lobe across the os from the main pla-centa. Vasa previa occurs in 1 in 2500 pregnancies. Rupture of a fetal vessel occurs rarely in pregnancy, but the risk is greatest with vasa previa. Rupture of a vessel can quickly lead to fetal death, as fetal blood volume is so small. Fetal mortality approaches 60% if rupture is not detected before delivery. When performing artificial rupture of membranes, it is important to ensure that no pulsating vessels are present which may represent a vasa previa.   An  Apt test  can help distinguish fetal blood from maternal blood.  ...

  UTERINE RUPTURE   Most cases of uterine rupture occur in the site of a prior cesarean delivery.    Uteran rupture  describes a spontaneous  complete transection of the uterus from endometrium to serosa. If the peritoneum remains intact, it is referred to as a  partial rupture  or  uterine dehiscence.  With complete rupture and fetal expulsion into the abdo-men, mortality ranges from 50% to 75%. Fetal survival depends in large part on whether the placenta remains attached to the uterine wall. Cesarean delivery is imperative to ensure neonatal survival and decrease maternal morbidity