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Low birth weight babies of different gestational age - transcript
From 23rd Annual Society for Maternal-Fetal
Medicine (SMFM) Conference held in San Francisco, California - February
2003
Low Birth Weight Babies of Different Gestational
Age
Tom Garite, MD interviewed by Hans van der Slikke, MD, PhD
Hans van der Slikke, MD, PhD: “It’s February the 7th, and we are at the meeting of the Society for Maternal Fetal Medicine in San Francisco and next to me today is Tom Garite, of the University of California, Irvine. Welcome!”
Tom Garite, MD: “Thank you.”
Hans van der Slikke, MD, PhD: “You did some beautiful research about the implication of the birth weight of pre-term babies and you had quite a number of data from your database. Could you please tell us about how you collected this data?”
Tom Garite, MD: “I work with a company called Paediatrics and Obstetrics, which is a large organisation that manages neonatology and perinatology practices across the United States and, since 1995, that company has been using an electronic medical record which generates progress notes and discharge summaries for neonatology practices in neonatal intensive care units.
Since that time, they’ve generated over 140,000 baby records. I started working with the company in 2001 and have worked with Dr. Reese Clarke, who is a neonatologist and manages the database. Reese and I have been interested in looking at some questions of obstetric interest in that rather robust database, so for this particular study, we included babies who were inborn so as, meaning delivered at the same hospital where they were admitted to the NIC so we would eliminate any bias from who was transferred and who wasn’t and we included babies between 23 and 34 weeks and we ultimately compared normally grown babies with growth-restricted babies.
We ended up, with a database that has just a huge amount of data in it. The database ultimately results from data from 124 neonatal intensive care units and it was for a five-year period from 1997 to 2002.”
Hans van der Slikke, MD, PhD: “And what was your definition of growth retardation?”
Tom Garite, MD: “Well, we used three definitions because we knew that if we used one, there would be somebody who could argue with our definition, so we looked at three different definitions. One was a diagnosis of growth-restriction made by the obstetrician based on ultrasound; the second was a diagnosis of small for gestational age made by the neonatologist on whatever basis he chose; the third was a birth weight for gestational age below the tenth percentile based on birth weight data that had been generated by the same database that’s been previously published, and so we used all three of those diagnoses and then as a fourth category, we used any one of those diagnoses. The remarkable thing is that the data are concordant, no matter which definition you use, for all of the end points that we evaluated, so it really didn’t matter.”
Hans van der Slikke, MD, PhD: “That was surprising.”
Tom Garite, MD: “But it’s good because it keeps everybody from defocusing and worrying about the definition.”
Hans van der Slikke, MD, PhD: “And then the next step?”
Tom Garite, MD: “Well, we were interested in a number of things. One is that to look at the absolute impact of growth restriction on mortality. One of the problems an obstetrician has in making decisions on whether to deliver a baby that may have some jeopardy is, what is the unbalancing risk of leaving the baby in the uterus with the risk of delivering it? I don’t think you can make an intelligent decision unless you know the likelihood of survival if you do deliver the baby at that gestational age and, unfortunately, most people base that on survival for a gestational age, regardless of birth weight. So if you say, okay, a 23-week baby in my hospital has a 50% chance of survival, and that’s worth delivering the baby because it’s in trouble at this age, that’s fine, except if that baby is growth-restricted, the actual survival may only be only 20%.
Or if you’re at 34 weeks or 33 weeks, well, let’s use a better example: if you’re at 28 weeks and the baby is growth-restricted and there’s absent Doppler flow and you’re trying to decide "do I wait for a change in heart rate or do I deliver it now?" Well, knowing the fact that the survival for this baby at 28 weeks with an estimated foetal weight of 600 grams is much different than the survival at 28 weeks. So what we found is that at each gestational age, all the way up to about 31 weeks, was about a threefold worse survival, relative risk of mortality of about threefold, at each gestational age from 23 to 30, 31 weeks if the baby was growth-restricted by any of those definitions.”
Hans van der Slikke, MD, PhD: “I wonder if you also did the stratification if it was below the tenth percentile?”
Tom Garite, MD: “No, we didn’t see how bad that was and certainly the worse the growth restriction, the worse the mortality is going to be. We also wanted to look at morbidity and this was for another reason. There is a general impression in obstetrics that comes from, I think, bad data, that babies who are growth-restricted may, because of stress, whatever that is, perform better than other babies of equivalent gestational age.”
Hans van der Slikke, MD, PhD: “That’s RDS.”
Tom Garite, MD: “That’s RDS, especially. Now I think where that comes from, is what happens you get a 35-week baby and it’s only 1,200 grams and you say, "wow, that baby is doing pretty good for 1,200 grams", but maybe it’s not doing real good for 35 weeks and so the problem is it’s very hard to go to the literature and say, well, what’s the real expected performance, respiratory performance, of a baby who is 1,200 grams at 35 weeks or who is really 35 weeks. So you really need to compare a large cohort of babies at each gestational age increment, I know that.
So we looked at significant morbidity measurements and those are things that have an impact on adverse long-term survival and we looked at retinopathy of pre-maturity, we looked at intraventricular haemorrhage, we looked at being on the respirator at 28 days which has a correlation with chronic lung disease and we looked at necrotising enterocolitis and, again, at each gestational age increment up to that 31 weeks, babies with growth restriction who did survive, were about one-and-a-half to twofold more likely to have any or all of these morbidities, so I would say that this helps to put that myth about improved respiratory function, and all other functions, to rest.”
Hans van der Slikke, MD, PhD: “And just for my understanding, these were all spontaneously born children, as well?”
Tom Garite, MD: “No, I think it’s a good mix of everything and one of the real weaknesses of doing studies from this database, is they’re very limited obstetrically, so we don’t know the reasons for delivery. All we know is the route of delivery, we know whether they received steroids and other than that, we don’t have much data.”
Hans van der Slikke, MD, PhD: “And maybe the condition at birth?”
Tom Garite, MD: “Right, Apgar scores.”
Hans van der Slikke, MD, PhD: “You could argue that the babies, small birth weight babies, have a significant higher risk of being born in a bad condition.”
Tom Garite, MD: “That’s correct.”
Hans van der Slikke, MD, PhD: “Well, so the main thing you showed is that it’s in, well, there are really bad risks, the small ones.”
Tom Garite, MD: “Right, and I think it’s very important for obstetric decision-making to have all the information available that you need to make the right decision and we have a lot of information about how the baby is doing in utero based on Doppler and heart rate, biophysical profile, amniotic fluid volume. So, we know when the baby is in trouble, but to weigh the risk of delivery as opposed to just leaving the baby in utero, you really need to know for that gestational age, for that given weight, what is really the outcome if that baby is delivered.”
Hans van der Slikke, MD, PhD: “And even the next step would be to know how this risk is in your hospital.”
Tom Garite, MD: “Sure, and I think that’s a really good point because maybe that will encourage people instead of just looking at morbidities and mortalities at given gestational ages to break that down into normally and abnormally grown babies.”
Hans van der Slikke, MD, PhD: “I can imagine it’s challenging. Did you have the occasion of comparing different centres?”
Tom Garite, MD: “No, we didn’t do that. No, there are too many pitfalls in trying to do too many sub analyses of these data, you know. We try to remember these are database-driven studies which have real limitations and the more you try to sub analyse this, the more you get into data that’s probably not as meaningful because the power of this particular study is in the numbers, to have a study with 35,000 babies and, you know, 3,000 babies who are growth-restricted is huge because you can’t generate gestational age-specific morbidities and mortalities and once you start breaking them down to every week of gestation, you would get such small numbers and you need such large numbers of babies to do that. If you then further subdivide that by hospital of delivery, whatever, you’re starting to get into such small numbers, even smaller numbers.”
Hans van der Slikke, MD, PhD: “Okay, thank you very much.”
Tom Garite, MD: “It’s my pleasure. Thank you for having me.”
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