Temporary elevated insulin-like growth factor I during lactation

The measuring of hormones during lactation can result in interpretation difficulties. A 30-year-old woman presented with suspected jaw overgrowth and increased insulin-like growth factor I (IGF-I) (52 nmol/L; reference range 10-40 nmol/L). No other signs of acromegaly were found. She was breastfeeding eight times per day, and when she decreased her breastfeeding to three times per day, IGF-I decreased (41 nmol/L). After the cessation of lactation, IGF-I was normalised (22 nmol/L). No confounding factors which could affect the IGF-I levels, such as nutritional or metabolic factors, were found. Her menstrual cycle was regular all the time. Magnetic resonance imaging of the pituitary gland showed a probably unrelated microadenoma. All other pituitary hormones were normal, indicating that the microadenoma was non-functional. In conclusion, this unique case suggests an association between the frequency of lactation and IGF-I levels, and demonstrates the difficulties encountered when measuring hormones during breastfeeding.