Objective: To develop guidelines for recognizing stages of fetal skin development to allow objective assessment of gestational age.
Methods: Three hundred seventy-nine human fetuses with known gestational ages of 12-30 weeks were examined at autopsy. Skin samples were taken from the abdomen. Two hundred fifty samples constituted a reference to establish histologic criteria from the development of skin appendages, hair, and apocrine and eccrine glands. One hundred twenty-nine additional skin samples were evaluated as a test set by the same investigators without knowledge of the condition of pregnancy or gestational age.
Results: The assessment of 250 skin samples allowed a description of those features that are suddenly discernible and can be used to determine gestational age as having reached or passed weeks 14, 16, 18, 20, 23, 25, and 29 or 30 (after the last menstrual period). Two examiners assessed these histologic features in a random and masked manner in the 129 skin samples of the test set. A 97% agreement with the actual gestational age of the fetus was achieved.
Conclusion: Skin development is a continuous process, but some discrete patterns are strongly related to fetal age, are easy to recognize, and are insensitive to artifacts. In our institution, they have become indispensable in evaluating fetal and neonatal pathology.