IVF Birth Weights Show Steady Increase Over Three Decades Interview with:
Prof. Daniel R Brison PhD, FRCPath
Scientific Director
Department of Reproductive Medicine
Manchester University NHS Foundation Trust
Old St. Mary’s Hospital
Manchester U.K and

Catherine M Castillo PhD
Maternal & Fetal Health Research Centre
Division of Developmental Biology and Medicine
School of Medical Sciences, Faculty of Biology, Medicine and Health
The University of Manchester What is the background for this study? What are the main findings?

Response: IVF conceived children have been known to have poorer birth outcomes when compared to spontaneously conceived children. Even when excluding twins and triplets, which result from more complicated pregnancies, IVF singletons have an increased risk of low birth weight and being born small for “dates” (length of gestation).  This is important as studies carried out in non-IVF children show that low birth weight is associated with slightly higher risk of disease in later life.

We knew from the literature that birth outcomes differed within the IVF population depending on the type of treatment used; for example, singletons conceived from frozen/thawed embryos are born with higher average birth weights when compared to their fresh embryo conceived counterparts. Our research team wanted to investigate whether IVF practices and technologies per se (which have advanced quite rapidly over the years since 1978 when the first IVF baby was conceived) were associated with differences in singleton birth weight.

In attempting to quantify historical changes in laboratory practice going back as far as we could, we discovered that our outcome of interest – birth weight – had indeed increased notably throughout the time period covered by the available data. Besides observing an increase in birth weight of almost 180g over the study period (when accounting for child gender, gestational age and maternal parity), we also observed that frozen embryo transfer was associated with higher birth weight, and spontaneous fetal reduction and longer duration of infertility were associated with lower average birth weight. What should readers take away from your report?

Response: Although we couldn’t pinpoint any causal relationships between specific IVF practices and birth weight, we were able to observe that IVF singleton birth weight has increased steadily over a number of years; a change that has occurred alongside the rapid evolution of technologies in the IVF laboratory – only some of which we were able to include the current study such as culture media composition, incubators, and other aspects of modern embryo culture systems. This is reassuring, as it suggests that while the older generation of IVF children may experience a slightly higher chance of problems associated with low birthweight, the newer generation being born now are less likely to.  Interesting, children conceived without IVF in the UK during the same period do not show any increase in birthweight, so this seems to be specific to IVF-conceived babies. What recommendations do you have for future research as a result of this work? 

Response: Multi-centre studies that capture more variation in IVF practices and laboratory technologies are needed; these should also combine detailed IVF-specific data with detailed information about the couples going through IVF in order to account for potential parent-related confounders.   We would also like to see more centres which have records going back 20 or 30 years doing their own studies of this type, to enable us to understand whether this is a widespread change, or something specific to just our centre.  We would also like to see fertility regulators collecting more data on important clinical and laboratory variables to allow national studies of this type. Is there anything else you would like to add?

Response: We would like to highlight that this work, on the growth and health of UK IVF children, was funded entirely by grants from the European Union, and not from UK grant bodies.  This is in part because this type of research requires international collaboration as well as funding.

We have no commercial disclosures to report.


Catherine M Castillo, Gregory Horne, Cheryl T Fitzgerald, Edward D Johnstone, Daniel R Brison, Stephen A Roberts; The impact of IVF on birthweight from 1991 to 2015: a cross-sectional study, Human Reproduction 

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Last Updated on March 19, 2019 by Marie Benz MD FAAD