Hematological Status, Blood Rh


Hemoglobin and hematocrit

Abnormal maternal hematological status, defined as both low and high hemoglobin (Hgb) hematocrit (Hct) values, may potentially be associated with adverse pregnancy outcomes for the infant as well as the mother. The initial test should be done as early as possible in the pregnancy.

The normal range of hemoglobin value in the nonpregnant healthy adult female is 14 " 2 g/dL However, a large majority of women in the reproductive age have hemoglobins in the lower end of this range (12 to 13 g/dL). During pregnancy, the hematocrit and hemoglobin concentration begins to fall during the first trimester as the plasma volume expands more rapidly than the red cell mass.

Most of the plasma volume increase occurs before the third trimester, but the red cell mass steadily increases until term, resulting in a continued rise of hemoglobin in the third trimester. In normal pregnancy, therefore, most women experience a lowering of hemoglobin and hematocrit in the second trimester and a rise in the third. Early in the third trimester, at 26 to 28 weeks, the hemoglobin and hematocrit level should be measured again. This test should again be repeated at 32 - 36 weeks gestation. The extent to which a decrease in hemoglobin can occur and still be considered physiologic is unclear, and, therefore, it is difficult to define anemia in pregnancy.

However, in various epidemiologic studies the lower limit for hemoglobin concentration has ranged from 10 to 12 g/dL. The value of 10 g/dL is often considered as approximating the demarcation between physiologic fall of hemoglobin and the presence of true anemia. In the postpartum phase and in women's health visits, hemoglobin and hematocrit should be performed as indicated by history and physical examination.

Blood Rh, Rh negative titer, antibody screen

The Rh antigen was identified by Landsteiner and Weiner in 1940. Rho(D) immune globulin (RhoGam) was introduced in the United States in 1963 for the prevention of Rh sensitization in women with Rh-negative blood. These developments have significantly improved the outcomes of pregnancy for Rh-negative women and their infants.

Rh(D) isoimmunization is one of the most common forms of blood group incompatibility between mother and fetus. It can cause extensive destruction of fetal red blood cells leading to significant morbidity and mortality in the fetus and newborn infant. Prior to the advent of effective prophylaxis, between 0.5 percent and 1.0 percent of all pregnant women were Rh(D) isoimmunized

Rh(D)-positive infants born of Rh(D)-negative mothers who have been sensitized to the red cell antigen during a prior pregnancy or via blood transfusion are at risk for red cell destruction in utero.

This hemolytic process occurs when anti-Rh(D) immunoglobulins cross the placenta from the maternal to the fetal circulation. The circulating antibodies attach to fetal Rh(D)-positive red cell membranes and initiate the hemolytic process. This process increases bilirubin production in infants, which can potentially produce permanent brain damage. More importantly, severe hemolytic anemia can cause tissue hypoxia, heart failure, and gross anasarca of the fetus, a condition often referred to as hydrops fetalis.

Current recommendations state that all pregnant women should be screened for Rh blood type and Rh(D) antibodies, and many authorities suggest screening for atypical antibodies known to cause hemolytic anemia of the newborn. Screening at the first prenatal visit will identify the 15 percent of Caucasians and four percent to eight percent of Black women at risk for Rh(D) isoimmunization as well as the 1.6 percent of pregnant women sensitized to atypical red cell antigens. Those at risk for Rh(D) sensitization are again screened for anti-Rh(D) antibody at varying intervals during pregnancy. Once a sensitized woman has a significant titer against red cell Rh(D) or an atypical red cell antigen, management focuses on identification of fetal anemia and its consequences.

An unsensitized, Rh-negative patient should have another antibody test at approximately 28 weeks of gestation. If the patient is still unsensitized, she should receive Rho(D) immune globulin prophylactically. In addition, any unsensitized, Rh-negative patient who has an ectopic gestation, undergoes abortion (either spontaneous or induced), or has a condition associated with maternal-fetal hemorrhage (e.g., abruptio placentae) should receive Rho(D) immune globulin unless the father is Rh negative.