Placental ratio and fetal growth pattern

Placental hypertrophy and reduced fetal growth have been postulated to be an adaptation to maintain placental function in pregnant women with complications such as malnutrition. If this is true, a pregnancy with impaired fetal growth, resulting in a small for gestational age (SGA) infant, should have an increased placental weight to birthweight ratio (placental ratio) compared to those with appropriate for gestational age (AGA) or large for gestational age (LGA) infants.

To determine the relationship between placental ratio and fetal growth pattern.

Labour and delivery data of 1000 deliveries in the Department of Obstetrics & Gynecology, Siriraj Hospital from January 2001 to June 2001 were retrospectively studied to compare the placental ratios among pregnancies with SGA, appropriate for gestational age (AGA) and large for gestational age (LGA) infants.

From 96 SGA, 804 AGA and 100 LGA cases, a higher placental ratio was found in the SGA group compared to AGA (0.2074 and 0.1985 respectively, p = 0.013). However, actual placental hypertrophy was not found as demonstrated by a lower placental weight in SGA compared with AGA pregnancies of the same birthweight range. There was no significant difference in placental ratio between the LGA and AGA group, the ratios being 0.2020 and 0.1985 respectively (p = 0.260). Although a positive correlation between placental weight and birthweight was observed in the AGA and LGA groups, it was not demonstrated in the SGA infants. This might influence the placental ratio in the SGA group.

SGA pregnancies are associated with an increased placental ratio which appears not to be due to placental hypertrophy. As reduced birthweight has been shown to be correlated to diseases in adult life, whether this association between SGA and an increased placental ratio will have an implication in future obstetric care and prediction of diseases in adult life remains to be elucidated.