The influence of maternal hematocrit on placental development from the first to the second trimesters of pregnancy

OBJECTIVES: To study the influence of maternal hematocrit (Ht) and hemoglobin (Hb) levels on placental size and growth in the first and mid-second trimesters of pregnancy.

SUBJECTS/METHODS: This was a prospective study performed at the fetal medicine unit of a university hospital. One hundred and eighty-one women with a singleton pregnancy were recruited at 11-14 weeks' gestation. For each case three scans of the placenta were performed, the first at recruitment and the following two at 3-week intervals. The volume of the placenta was measured at each visit using a three-dimensional ultrasound scanner. The maternal Hb and Ht were measured within 2 weeks of the first scan.

RESULTS: The placental growth during the second trimester was inversely related to the Ht levels (r = -0.29, P = 0.001). It was also related to the Hb level (r = -0.20, P = 0.021). An increase of 0.1 units of Ht was associated with 38% less growth of the placenta (95% confidence interval: 18-54% less growth).

DISCUSSION: This study demonstrates the effects of maternal environment on placental growth. Our data suggest that the levels of Ht appear to affect the placental growth during the second trimester. Further studies on the factors that regulate placental growth are needed to elucidate the pathophysiology of these interactions and their effect on pregnancy outcome.