Repeated hematocrit measurements in low-risk pregnant women.

OBJECTIVE

To determine the incidence of anemia in the third trimester among women with normal hematocrits early in pregnancy.

STUDY DESIGN

Low-risk women seeking prenatal care were identified. Patients with a hematocrit >33% in the first or second trimester and a hematocrit drawn in the third trimester were included. Rates of anemia; hematocrit <33%; and severe anemia, hematocrit < 30%; were determined. The primary outcome was the development of anemia in the third trimester.

RESULTS

A total of 1,604 women met inclusion criteria; 16.2% of women became anemic, and 4.5% became severely anemic in the third trimester. Using a starting hematocrit value of 39% as a cutoff, only 66% of women would need to be rescreened in the third trimester in order to detect 78.5% of anemias (sensitivity 78.5%, specificity 39.7%, negative predictive value 90.5%).

CONCLUSION

The percent of women with normal hematocrits in the first trimester who become anemic in the third trimester is 16.2. Hematocrit screening in the third trimester may be unnecessary for low-risk women with starting hematocrits > 39%.