Objective: This study aims to determine if nucleated red blood cells are elevated in pregnancies that continue beyond 289 days of gestation.
Study design: Cord blood was prospectively collected from term and post-term singleton gestations from August 1 to December 31, 1998. Umbilical artery nucleated red blood cells were counted per 100 white blood cells. The comparison was made between pregnancies ending at 261-289 days (37.1-41.2 weeks) of gestation and those ending after 289 days (> or = 41.3 weeks) of gestation.
Results: Cord blood from 304 cases was obtained and evaluated for nucleated red blood cells per 100 white blood cells. The mean value of nucleated red blood cells per 100 white blood cells in the post-term neonate group was significantly higher than in the term neonate group (median 6.5, range 0-24 vs. median 3.7, range 0-14; p < 0.05). The values did not vary by fetal presentation, mode or duration of delivery. Neonatal outcome was comparable between both study groups.
Conclusion: In post-term gestation after 289 days nucleated red blood cells in cord blood are significantly increased. These results point towards a different fetal oxygenation in post-term pregnancies beyond 289 days of gestation and support the current practice of very close testing of fetal well-being under those circumstances.