Placental weight and placental weight to birthweight ratio in relation to Apgar score at birth: a population study of 522 360 singleton pregnancies

Abstract

Objective: To study whether placental weight or placental weight to birthweight ratio are associated with Apgar score in the newborn 5 min after birth.

Design: Population-based registry study.

Setting: The Medical Birth Registry of Norway.

Population: All singleton live births during the period 1999-2008, a total of 522 360 births.

Methods: The placental weight to birthweight ratios were divided into quartiles within 2-week intervals of gestational age at birth, hence 25% of the pregnancies were within each group. We studied the proportion of pregnancies in the highest quartile of placental weight and placental weight to birthweight ratio according to Apgar score 5 min after birth, and estimated the odds ratio for Apgar score ≤7 if the placental weight to birthweight ratio was in the highest quartile, and used the lowest quartile as reference.

Main outcome measure: Apgar score in the newborn 5 min after birth.

Results: In births after pregnancy week 29, and at every 2-week gestational age interval, the mean placental weight and placental weight to birthweight ratio were higher in newborn with Apgar score ≤7 than in infants with Apgar >7. The crude odds ratio of Apgar score ≤7 was 1.65 (95% CI 1.57-1.74), comparing the highest to the lowest quartile of placental weight to birthweight ratio. Adjustments for gestational age, birthweight, infant sex, maternal age, preeclampsia, diabetes and congenital malformations did not alter the odds ratio significantly.

Conclusions: Placental weight and placental weight to birthweight ratio were higher in pregnancies with infant Apgar score ≤7 compared with Apgar score >7.

Keywords: Apgar score; Placental weight; birthweight; gestational age; population study.