|Professor Louise Kenny standing by the Pea Pod|
As obesity levels in Ireland rise, assessing neonatal body composition with the sophisticated Pea Pod instrument could have a major impact on the health of the nation, writes Eimear Vize
We are what we eat, and that old adage rings true even before we are born. Numerous studies have already confirmed that babies born to overweight and obese women have a higher risk of birth defects and even death. Irish doctors are now exploring how the weight and diet of a mum-to-be influence their unborn babies, from the infant’s weight and physical condition at birth, to the long-term health impact.
This investigation of thousands of babies and their mums is being made possible through two major research efforts underway at the Cork University Maternity Hospital (CUMH) and University College Cork (UCC) - the SCOPE study, which records important information about mothers from early pregnancy, and the BASELINE study, in which these infants are monitored as they grow and develop.
“Since these studies began in 2008, we now have data on more than 2,000 babies in Cork who were born to 2,000 first-time pregnant mums,” says Prof Louise Kenny, principle investigator of the Health Research Board funded SCOPE study, Professor of Obstetrics at UCC and consultant obstetrician and gynaecologist at CUMH.
“We have very detailed information about the mums including their weight, body mass index and skin fold thicknesses, and we’re tracking their babies from 15 weeks gestation and birth, through to the age of five, and hopefully on into adulthood.
“We’re looking at how early life influences, such as in utero experiences, and how they are fed immediately after delivery, affect their future health and wellbeing.”
A key tool in this endeavour is the charmingly named Pea Pod – the world’s only air displacement plethysmography (ADP) system to determine body composition (fat and fat-free mass) in infants between birth and up to six months of age.
Essentially a scaled down version of the adult-sized Bod Pod, this sophisticated instrument is used to measure and monitor changes in body fat stores of infants. The Pea Pod measurement takes about two minutes to complete and provides information can be used to better define the nutritional requirements needed to support healthy growth, as well as possibly providing early identification of children at risk for obesity.
Cork University Maternity Hospital was the first in the country to take delivery of the Pea Pod system in 2009, as part of the SCOPE study. A second device was installed soon after at the Coombe Women and Infants University Hospital in Dublin.
“Air displacement plethysmography is the technique of measuring body fat, as opposed to total bodyweight. This technology been around for over a decade but was used only for adult patients, called the Bod Pod. It basically assesses not just how heavy a patient is but how much fat they have on board. Weight is quite a crude way of looking at someone’s general health and wellbeing because you can be heavy but tall and quite lean, and obviously that’s not the same as being short and mainly covered in fat,” Prof Kenny remarks.
“So the Pea Pod is a mini version of the Bod Pod, and it’s used for assessing neonatal body composition. It can be used in newborns up to about two to three months of age, certainly no further than six months. After that they start getting a little too big to fit in.”
Researchers in Cork have thus far completed the world’s largest series of baby measurements in the Pea Pod. At one point, they were assessing up to five babies a day.
“Well over 1000 babies have been measured in the pod, and of those infants, most have been measured twice so we’ve actually done well over 2,000 measurements. As we are the first group to have assessed that many babies, we’re building up a good general idea of what body composition is in newborns. For example, in our Pediatrics paper*, The BASELINE team, funded the National Children's Research Centre and led by Dr Deirdre Murray, found that girl babies are a little bit fatter than boys, and that fat is very much dependent on gestational age. Put simply, the longer you are left inside perhaps not surprisingly the more fat you have. And this is information that is new.”
While female infants had a greater percentage of body fat than male infants at each gestational age, the researchers found that male infants had actually heavier at birth than their female counterparts, meaning that this increase in weight in male infants was due to increased fat-free mass.
Utilising the results from their study of the first four days of life of almost 800 infants, the Cork team created a centile chart for body fat percentage in male and female infants that will assist doctors and researchers in the interpretation of measured neonatal body fat percentage.
“Epidemiologic studies have demonstrated reduced glucose tolerance and increased obesity, cardiovascular disease, dyslipidemia, and obstructive airway disease in adults who were exposed to inadequate nutrition in utero. This foetal programming for adult disease begins in utero, and estimation of percentage body fat at birth may have a role in identifying infants at risk,” the authors suggest.
Overweight and obesity is a serious problem in Ireland affecting between 18% and 27% of Irish children. In fact, Ireland currently ranks second highest in obesity rates in the European Union. Minister for Health James Reilly says he is determined to introduce strong measures to tackle childhood obesity, telling the Dail recently: “If we do not address it, we may end up the first generation to bury the generation behind it.”
As a result, the prevention and treatment of obesity has become a top research priority and the Pea Pod body composition tracking system is a critical tool in this endeavour.
The air displacement plethysmography (ADP) used by the Pea Pod unit is similar in principle to hydrostatic (or "underwater") weighing but uses air instead of water to measure body volume, based on the physical relationship between pressure and volume. Obviously, air is more convenient, safe and comfortable than water, particularly when assessing infants.
Once body volume is determined, the principles of body density, or densitometry, are used to calculate body composition. In densitometry, the more dense a body is, the lower the percentage of body fat; the less dense a body is, the higher the percentage of body fat.
By all accounts, the Pea Pod is a non-invasive and comfortable environment for infants. The baby is placed in the PEA POD test chamber tray and enters a warm, pressure-controlled chamber the size of a crib for a two-minute volume measurement. During the entire period the infant is clearly visible through the unit window. The test results are then computed, displayed and printed.
Research using the Pea Pod at the Coombe Women and Infants University Hospital in Dublin confirmed that neonates of mothers with a normal BMI have significantly less body fat than neonates of overweight and obese mothers. However, there was a wide range in body fat percentages for infants of both maternal BMI groups, which was not fully explained by the parameters of birth weight and neonatal abdominal circumference alone. The Coombe research team are currently investigating other maternal factors that may determine neonatal body fat percentages.
Meanwhile, researchers in Cork are examining how body composition, or fat, changes in early childhood.
“With regard to childhood obesity, obesity in adolescence and obesity in adult life, there is a lot of evidence now that the seeds are sewn in the early days of life, even in the womb, but certainly in the first few months of life,” says Prof Kenny.
“We’re using the Pea Pod to measure the babies as soon as they are born to see how much of their body composition is proportionally fat, and how that affects their health and growth and wellbeing as they develop. These babies are part of a large birth cohort that we’re following until they are five and hopefully into adulthood,” explains Prof Kenny.
There are a number of birth cohort studies worldwide, but few, if any of them will have such detailed information about the babies from before they are even born, right back to the first weeks of pregnancy.
Prof Kenny is also peripherally involved in another study that is examining how body fat composition changes in premature infants depending on the feeding regime they are put on.
“The Pea Pod is an important academic instrument. It is used primarily for research purposes at the moment but I can see a time then the Pea Pod might be of clinical use. For example, if we knew that a particular baby was of a certain birth weight but had a higher fat composition that would be a red flag and may call for earlier intervention to prevent childhood obesity.”
*Hawkes C, Hourihane J, Kenny L et al. Gender- and Gestational Age–Specific Body Fat Percentage at Birth. Pediatrics 2011; 128(3): e645-e651