Background: Physiological changes during pregnancy may affect laboratory parameters. Reference values based on samples from non-pregnant women are not necessarily useful for clinical decisions during pregnancy. There is a need to establish reference values during pregnancy in order to recognize pathological conditions. Methods: Eight hundred and one women with expected normal pregnancies were included in the study. Of these, 391 had no complications during pregnancy, delivery, or the early postpartum period. Blood samples were obtained at gestational weeks 13-20, 21-28, 29-34, 35-42, at labor, and 1 and 2 days postpartum. Reference intervals were calculated for 36 tests as recommended by the International Federation of Clinical Chemistry and Laboratory Medicine. Results: Many tests showed such large variations indicating that gestational age-specific reference intervals were necessary. Other tests had different but stable values when compared to non-pregnant women. A minor decrease in albumin levels was observed. This was not only due to pregnancyassociated hemodilution, since other components with the same or a larger molecular diameter did not show a similar decrease. Many tests exhibited a broad distribution around vaginal delivery and in the early postpartum period. Conclusions: Only a few parameters were unaffected during uncomplicated pregnancy, delivery, and the early postpartum period suggesting that implementation of gestational agespecific reference intervals is necessary. Clin Chem Lab Med 2010;48:237-48.

The CA-125 cut-off value (<35 U/mL) used for non-pregnant women can be used for women during pregnancy after gestational week 13 as a supplement to ultrasound evaluation of ovarian cysts. The wide range of CA-125 concentration during normal pregnancies makes it unlikely that small fluctuations in CA-125 can be clinically useful for identifying other conditions. Measuring CA-125 around the time of delivery is not recommended. Gestational age-specific reference intervals during normal pregnancy are not needed.

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