THIRD-TRIMESTER LABORATORY TESTS
A 33-year-old woman (G4 P3) is at 25 weeks’ gestation. Her height is 63 inches and she weighs 250 pounds. She has gained 30 pounds thus far this pregnancy. With her last pregnancy she gained 60 pounds, was diagnosed with gestational diabetes, and delivered a 4,300-g female neonate by cesarean section. She wants to know whether she has diabetes with this pregnancy.
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Chapter 5 l Prenatal Laboratory Testing
Diabetic Testing
H 50-g oral glucose tolerance test (OGTT )
This screening test is administered to all pregnant women between 24 and 28 weeks’ gestation. No fasting state is needed. A 50-g glucose load is given, and serum glucose is measured 1 h later. A normal value is <140 mg/dL. Fifteen percent of pregnant women will have an abnormal screen-ing test, which is >140 mg/dL. Management is a 3-h 100-g OGTT.
H 100-g OGTT
This is the definitive test for glucose intolerance in pregnancy. Fifteen percent of women with an abnormal screening test will be found to have gestational diabetes mellitus. After an overnight fast, a fasting blood sugar (FBS) is drawn. An FBS >125 mg/dL indicates overt diabetes mellitus, and no further testing is performed. If the FBS is <126 mg/dL, administer a 100-g glucose load, followed by glucose levels at 1, 2, and 3 h. Normal values are FBS <95 mg/dL, 1 h <180 mg/dL, 2 h <155 mg/dL, and 3 h <140 mg/dL. Gestational diabetes is diagnosed if ≥2 values are abnormal. Impaired glucose intolerance is diagnosed if only 1 value is abnormal.
Complete Blood Count (CBC)
Anemia
A CBC should be performed between 24 and 28 weeks’ gestation in all women. With the increasing diversion of iron to the fetus in the second and third trimester, iron deficiency, which was not present early in pregnancy, may develop. This is particularly so in the woman who is not taking iron supplementation. A hemoglobin <10 g/dL is considered anemia. The most common cause is iron deficiency, which occurs only after bone marrow iron stores are completely depleted.
Platelet count
Reassessment of pregnancy-induced thrombocytopenia can be also be done with the CBC.
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Atypical Antibody Screen
Before giving prophylactic RhoGAM to an Rh-negative woman, an indirect Coombs test is performed at 28 weeks. This is obtained to ensure she has not become isoimmunized since her previous negative AAT earlier in pregnancy. Two-tenths of a percent of Rh-negative women will become isoimmunized from spontaneous feto-maternal bleeding before 28 weeks. If it is discovered that the patient already has anti-D antibodies, administration of RhoGAM is futile.
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| S2 OB-GYN.indb 46 | 7/8/13 6:35 PM | |||
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| Late Pregnancy Bleeding | 6 | |
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