The Childbearing Years: A Teachable Moment for Weight Control?

Published on 6 February 2014 in Food, health and wellbeing

Introduction

Both pre-pregnancy maternal underweight and obesity are associated with a myriad of adverse pregnancy outcomes for both mother and child, which impact their immediate health and wellbeing, and draw substantially on limited NHS resources.

Women who are underweight at conception (1 in 20 pregnancies) are at risk of premature delivery and low birth weight while at the other end of the BMI spectrum, maternal obesity (1 in 5 pregnancies) is commonly associated with a plethora of risks that generally increase with degree of overweight. These include hypertensive disorders such as pre-eclampsia, gestational diabetes, stillbirth, operative delivery, large for gestational age and preterm birth.

Avoiding the consequences of these BMI extremes by encouraging women to achieve a healthy BMI prior to their first pregnancy is a laudable goal but it is important to recognise that many of these pregnancies are largely unplanned. This is particularly true for younger and socially deprived women who predominate in the underweight and obese BMI categories, respectively.

The inter-pregnancy period may be a “teachable moment” when women are more receptive to guidance to achieve or maintain a healthy weight and thereby optimise pregnancy outcome in their second and subsequent pregnancies. However it is imperative that this guidance is evidence based and applicable to all women across the BMI range. Accordingly we have recently investigated the relationship between inter-pregnancy BMI change (both weight loss and weight gain) and the risk of experiencing pregnancy complications in the second pregnancy.

Key Points

• Underweight and obese women are most likely to deliver babies prematurely and at the birth weight extremes.
• Both young underweight and obese women of any age have high rates of unplanned first pregnancy.
• The concept of “getting in shape” prior to first pregnancy is a commendable objective but in reality modification of other behaviours known to influence pregnancy outcome (eg. smoking, drinking) rarely occurs before conception is confirmed.
• The inter-pregnancy period may be a teachable moment for diet and exercise interventions aimed at optimising maternal weight control and minimising complications in subsequent pregnancies.
• Establishing the relationship between inter-pregnancy weight change and pregnancy complication risk is an important first step for informing weight control strategies.

Research Undertaken

Using data contained within the Aberdeen Maternity and Neonatal Databank (AMND), the association between inter-pregnancy weight change and the primary risk of adverse pregnancy outcomes in the second pregnancy was investigated in 12,740 women with first-ever and second consecutive deliveries at Aberdeen Maternity Hospital. Height and weight were measured at the first hospital booking appointment for both pregnancies and adjusted to a standard week of gestation for all women.

Compared with women who were weight stable, weight loss (>1 BMI unit) between pregnancies was associated with a 46% higher risk of spontaneous preterm delivery and a 65% greater risk of small for gestational age (SGA) birth. In direct contrast, weight gain between pregnancies (>3 BMI units) increased the risk of pre-eclampsia, gestational hypertension, emergency caesarean section and large for gestational age (LGA) birth at the second pregnancy by 85, 82, 78 and 70%, respectively. The relationship between weight gain and pre-eclampsia risk was only evident in women who were overweight at first pregnancy (BMI >25 units), while that between weight loss and preterm delivery was confined to women with a healthy weight at first pregnancy (BMI <25 units). In contrast, the association between weight loss and SGA was independent of first pregnancy BMI suggesting that any downward movement in maternal BMI is likely to increase the risk of low birth weight.

The public health implications of these findings are considerable. The natural assumption is that women who were obese at the start of the first pregnancy are more vulnerable to excessive weight gain during that pregnancy and in the subsequent postpartum period. While this was true for approximately 25% of our study population, a considerable number of initially overweight and obese women (18 and 20%, respectively) lost weight between pregnancies thus theoretically negating the risk of many of the maternal and perinatal complications associated with weight gain but increasing their risk of low birth weight. While the consequences of large inter-pregnancy weight gains are arguably more serious for a woman’s long term health our results suggest that a degree of caution is required if health professionals promote weight loss at this time. This is particularly important as the effectiveness of dietary and lifestyle intervention strategies aimed at improving pregnancy outcome among both normal and obese women remain largely unproven.

The  AMND records placental weight at delivery and our analysis additionally revealed that weight loss between pregnancies increased the risk of having a small placenta (<10^th Centile after adjustment for gender, gestational age and parity) while weight gain increased the odds of having a large placenta (>90^th Centile) at the second delivery. The implication is that changes in maternal nutritional status between successive pregnancies impact maternal nutrient reserves at the start of the second pregnancy and hence the placental growth trajectory. As placental size, blood flow and nutrient transport functions primarily determine the growth trajectory of the fetus, alterations in placental growth may in turn be on the causative pathway to some of the pregnancy complications reported here.

Policy Implications

Author

Dr Jacqueline Wallace Jacqueline.Wallace@abdn.ac.uk

Topics

Food, health and wellbeing

Comments or Questions