Chap 2 Obs: Prenatal Laboratory Testing

First Trimester Laboratory Tests

Hemoglobin and hematocrit
Normal pregnancy range is 10-12 g/dl. This is less than range of non-pregnant woman because of greater plasma volume increase than RBC hence dilution anemia.

MCV
In pregnancy, most reliable predicate of anemia

Others

• Platelet count
• Leukocyte count
• Rubella IgG count
• Hep B surface antigen
• Direct and Indirect comb test
• Syphilis
• HIV (HIV is recommended for all pregnant woman, but requires specific consent). The most common risk factor for HIV in woman is contact with IV drug abuser

Second Trimester Laboratory tests

Materal Serum Alpha-Fetoprotein (MS-AFP)

This is major glycoprotein of embryo. The concentration peaks at 12 week in fetus and 30th week in maternal serum.

Elevated MS-AFP

• A positive value of >2.5 MoM
• Most common cause is dating error
• Most common pathological cause is Neural tube defect

Low MS-AFP

• A positive value of <0.85 MoM
• Most common cause is dating error
• Most common pathological cause is Down Syndrome

Triple Marker Screen

• It includes MS-AFP, estriol and hCG. 
• In Down Syndrome MS-AFP and estriol are decrease, but hCG is increase
• In Edward Syndrome (trisomy 18) all are decrease

Third Trimester laboratory tests

Diabetic Testings
normal value is less than 140 mg/dl

CBC
A cbc should be performed between 24 and 28th week gestation in all woman
A hemoglobin less <10g/dl is considered anemia

Atypical Antibody Screen
look for Rh factor