Biomathematics & Statistics Scotland
Extreme birth weights, whether high or low, tend to be associated with pregnancy complications and subsequent health problems for the baby. It is therefore important to be able to identify women at risk at an early gestational age. We have collaborated with the Rowett Institute of Nutrition and Health on analyses of the Aberdeen Maternity and Neonatal Databank, with a particular focus on the risk of pregnancy complications and their links with maternal weight and placental characteristics. The data showed that an increase in body mass index (BMI) between pregnancies is associated with an increased risk of complications in the second or later pregnancies, independently of the initial or final BMI, and that a key factor in these relationships is the placenta size. Knowledge of the distribution of placental weight at different gestational ages is important to identify extreme values, and to see if these are due to complications in the pregnancy. We derived and published a new set of centile curves to help identify low and high values for different gestational ages. These curves were estimated by fitting nonparametric smooth functions to the mean, variance and skewness of the observed distribution of placental weights at different gestational ages. It was found that placental weights during a first pregnancy tend to be lower than in later pregnancies, and that this had a greater effect than the gender of the baby. We also examined the centiles of the distribution of the fetal to placental weight ratio, and found that in this case parity did not have a significant effect.
The 3rd, 50th and 97th percentile
curves showing the development
of placental weight with
gestational age, for first (dashed
lines) and later (solid lines)
pregnancies leading to the birth of
baby girls.
Further details from: Graham Horgan
Article date 2013
