Pregnancy and laboratory studies: a reference table for clinicians

To establish normal reference ranges during pregnancy for common laboratory analytes.

We conducted a comprehensive electronic database review using PUBMED and MEDLINE databases. We also reviewed textbooks of maternal laboratory studies during uncomplicated pregnancy.

We searched the databases for studies investigating various laboratory analytes at various times during pregnancy. All abstracts were examined by two investigators and, if they were found relevant, the full text of the article was reviewed. Articles were included if the analyte studied was measured in pregnant women without major medical problems or confounding conditions and if the laboratory marker was measured and reported for a specified gestational age.

For each laboratory marker, data were extracted from as many references as possible, and these data were combined to establish normal reference ranges in pregnancy. When possible, the 2.5 and 97.5 percentiles were reported as the normal range. In some of the reference articles, however, the reported range was based on the minimum and maximum value of the laboratory constituent. In those cases, the minimum to maximum range was used and combined with the 2.5 and 97.5 percentile range. We found that there is a substantial difference in normal values in some laboratory markers in the pregnant state when compared with the nonpregnant state.

It is important to consider normal reference ranges specific to pregnancy when interpreting some laboratory results that may be altered by the normal changes of pregnancy.