In utero meconium passage in fetuses and newborns with myelomeningocele

The authors retrospectively investigated whether midgestational fetal myelomeningocele (fMMC) repair alters intrauterine meconium exposure.

Prior to the National Institutes of Health Management of Myelomeningocele Study, 54 fetuses underwent fMMC repair at the authors' institution. Forty-six fMMC sacs were available for pathological examination and 53 MMC sacs from postnatally repaired MMCs (pMMCs) were available for comparison. The presence and distribution of meconium were blindly evaluated using a grading system defined as follows: absent (no meconium present), mild (<10 meconium-positive histiocytes [MPHs]/hpf), moderate (10-25 MPHs/hpf), and severe (>25 MPHs/hpf). Hall's bile stain was used to confirm meconium and Prussian blue and Fontana Masson stains to exclude hemosiderin and melanin, respectively.

Compared to pMMCs (79%), meconium histiocytosis was less prevalent in fMMC sacs (57%; p=0.017). Meconium staining was completely absent in 43% of the fMMC sacs. Mild meconium histiocytosis was found in 35% fMMC and 61% pMMC sacs (p=0.035). There was no statistical difference between groups with moderate and severe meconium histiocytosis.

Meconium passage in MMCs can occur early in fetal life. Fetal MMC repair may reduce the duration of meconium exposure, thereby potentially limiting the toxic injury to the vulnerable neural elements.