Clinical review: Special populations - critical illness and pregnancy

Pregnancy is a normal physiologic process that is defined by the presence of the utero-placental complex. Physiologic changes associated with pregnancy may result in strain on organ systems with limited reserve and result in deterioration of pre-existing medical conditions (Table 1). In addition, a number of systemic disorders result from pathologies of the maternal-fetal interface. The pregnant patient may be admitted to intensive care because of diseases that occur only in pregnancy (Table 2), diseases that are worsened by pregnancy resulting in critical illness, diseases for which the pregnant patient is at elevated risk, and diseases co-incidental to pregnancy. This review will concentrate on pregnancy-induced diseases.Major obstetric hemorrhage is the leading cause of maternal mortality worldwide and is the most frequent indication for ICU admission [1-3]. It may occur antepartum or postpartum.Antepartum hemorrhage occurs in 1 in 20 pregnant women; in the majority of cases, there is no risk to the mother or fetus. Causes include abruptio placentae, placenta previa, placenta accreta/increta/percreta, and uterine rupture. Abruptio placentae (placental abruption) involves separation of the placenta from the decidua basalis prior to delivery. The patient may present with pain, vaginal bleeding, uterine tenderness, and increased uterine activity. Fetal heart rate abnormalities may be encountered. Depending on the location of bleeding, considerable blood loss may occur prior to diagnosis. Significant hemorrhage is associated with coagulopathy. Placenta previa involves implantation of the placenta in the lower part of the uterus and often is associated with a previous Cesarean section (CS) scar. Placenta accreta is an abnormally adherent placenta that implants in the uterine wall, usually in scar tissue following previous CS. With increasing severity there is placenta increta - invasion of the myometrium and placenta percreta - in which the placenta invades the extra-