Intrauterine Growth Restriction and Placental Location

Abstract

The site of the placenta within the uterus is likely to be an important factor in placental blood flow and consequently in the outcome of pregnancy. Placental location has been implicated in preterm birth, fetal malposition and malpresentation, and the risk of preeclampsia, but its association with fetal growth is not clear. This retrospective case-control study examined the relationship between placental location at mid-trimester and intrauterine growth restriction (IUGR), defined as a sonographically estimated fetal weight below the 10th percentile for gestational age using population-specific fetal growth curves. Participants were 67 women with well-dated singleton pregnancies who had IUGR and 205 who did not. Sonography was carried out at 16 to 20 weeks' gestation, and the relationship between IUGR and placental site was determined by multivariable logistic regression analysis. Black mothers made up a higher proportion of IUGR cases, but there were no group differences in maternal age, gravidity, parity, body mass index, or gestational age at the time of study. Anterior and posterior placental sites were most frequent in both IUGR cases and non-IUGR controls. After adjusting for potential confounding factors (including race, chronic hypertension, and hypertensive disorders of pregnancy), IUGR pregnancies were almost 4-fold more likely to have lateral rather than anterior or posterior placentation. The odds ratio was 3.8, with a 95% confidence interval of 1.3 to 11.2. Mean birth weight was about 2 kg lower in the IUGR cases than in non-IUGR control pregnancies. IUGR pregnancies had more antepartum and intrapartum complications, including antepartum steroid treatment, premature delivery, and cesarean delivery. In addition, neonates in the IUGR group were likelier to have 1- and 5-minute Apgar scores less than 5 and more often were admitted to the neonatal intensive care unit. More IUGR pregnancies ended in intrauterine fetal death, although the difference was not statistically significant. Significantly more IUGR infants died while hospitalized (4.5% vs. 0.5%). These findings, along with nonuniform distribution of blood flow to the uterus, suggest that placental location may be a major determinant of placental blood flow.