Placental ratio and anemia in third-trimester pregnancy

To perform a prospective, observational study in a tertiary center to determine whether anemia (hemoglobin level < 10 g/dL) developing in the third trimester was associated with an increased placental weight/birth weight ratio (placental ratio) and whether the placental ratio correlated with the hemoglobin level at different periods and with other factors, such as gestational age and parity.

A total of 476 nonanemic women with low-risk singleton pregnancies were recruited at their 28-30-week antenatal visit over a three-month period. Excluded from the final analysis were 20 women who delivered elsewhere and 19 found to be carriers of thalassemia traits due to their low mean cell volume. All women received standard obstetric care, and ferrous sulphate was prescribed for those who developed anemia.

Anemia developed in 45 (10.3%) of the remaining 437 women. This group had significantly decreased red cell indices, gestational age (38.3 +/- 2.0 vs. 39.2 +/- 1.3 weeks, P = .004) and birth weight (3,082 +/- 416 vs. 3,220 +/- 411 g, P = .035) but no difference in placental weight (609 +/- 102 vs. 594 +/- 108 g), so the placental ratio was increased as compared with that in the control group (0.196 +/- 0.026 vs. 0.185 +/- 0.026, P = .002). Multiple regression analysis confirmed that the placental ratio correlated only with the last hemoglobin level (P = .041).

Our results indicate that placental size increased relative to infant size in pregnancies complicated by anemia, but whether this phenomenon reflected actual placental hypertrophy or failure of fetal growth to keep up with placental growth remains to be determined.