THE ASSOCIATION BETWEEN SPONTANEOUS PRETERM BIRTH AND PLACENTAL HISTOLOGY AT HIGH AND LOW-ALTITUDE AREAS OF SOUTHERN SAUDI-ARABIA

Objective: To investigate the association between spontaneous preterm birth and placental histology at high and low altitude. Design: Cros-s ectional randomized prospective study. Setting: Mohayel (500 meters ab ove sea level) and Abha (3,100 meters above sea level), cities in sout hern Saudi Arabia. Subjects: Pregnant Saudi women living permanently a t the areas of study and placentae from spontaneous preterm birth with out an obvious cause. Methods: Paraffin sections of the placenta were stained by periodic acid schiff and hematoxyllin and eosin for identif ication of cytotrophoblastic cells and syncytial knots respectively by the light microscopy. The volume fraction of the fetal capillary lumi na and stromal tissue of the terminal villi was performed by the image analyser. Results: The total percentage of preterm birth was 1.93% at low altitude compared to 4.41% at high altitude (p<0.01). The percent age of preterm births without an apparent cause was 1.3% at low altitu de compared to 3.3% at high altitude (p<0.01). The histology of the te rminal villi of placentae, comparing high with low altitude, showed, r espectively, syncytial knots in 45.4% and 13.1% (p<0.001) and cytotrop hoblastic cells in 52.7% and 28.6% (p<0.001) of the villi. In addition , comparing high to low altitude, there was a significant fall in the fractional volume of their stromal tissue (p<0.001) and an equivalent rise in the fractional volume of their foetal capillary lumina (p<0.00 5). Conclusion: It is concluded that stimulation of syncytial knots fo rmation, persistence of villous cytotrophoblastic cells and hypercapil larization are Since, it is known that placental hypoxia is associated with increased incidence of spontaneous preterm birth, it is suggeste d that high altitude may be involved in the aetiology of spontaneous p reterm birth.