The Effect of Antenatal Corticosteroids on the Fetal Thymus - a Possible Role in Fetal Immune

Women with a singleton pregnancy in the twenty-forth to thirty-fourth week of gestation who are at risk for preterm labour, requiring the administration of Betamethasone twelve milligrams intramuscularly every twenty-four hours for two doses will be included in this study along with an equal number of gestational-age matched controls not at risk for preterm delivery and therefore not requiring the administration of Betamethasone. A 2-D ultrasound assessment of the fetal thymus size with measurements of the maximum transverse diameter and thymus perimeter in the three-vessel view will be performed as a baseline measurement within 36 hours of the administration of the first dose of corticosteroids. For each patient enrolled, a gestational-age matched control will have a similar ultrasound assessment. These measurements will be repeated 2 weeks after the first baseline ultrasound, and then only patients who received corticosteroids will have subsequent ultrasound measurements every 2 weeks until delivery.