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Effects of assisted reproductive technology (ART) on long-term birth weight trends: a national cohort study

Chief investigator: Stephen Roberts
Research establishment: University of Manchester
Year of approval: 2020

Lay summary

This research is being conducted to potentially help with improving IVF procedures for better child health outcomes, growth and adult health of Assisted Reproductive Technology (ART) babies. Prior research established that IVF has an impact on birthweight, and that low birthweight has an effect on future health outcomes. A single-centre study reported that birthweight of ART-conceived babies had increased over time. This project therefore aims to explore the impact of IVF procedures on the birthweight trends for a nationally representative group of ART babies using HFEA data of treatments undertaken between 1991 and 2018 and compare these changes to those observed in a nationally representative group of naturally conceived babies born in a relative period of time.

The project also aims to explore some methodological issues associated with the HFEA data (which is commonly used in fertility research) and help inform future ART researchers on how best they can use the HFEA data in order to achieve improved and productive research outcomes. Patients are asked whether they are willing to disclose their personal data for research purposes and only personal data of the patients who gave their consent can be provided to researchers. A particular concern this study will investigate is that a low rate of consent for disclosure will lead to incomplete datasets for any research requiring more than minimal data and potentially serious bias in any conclusions.

A subsidiary project will look at the impact of pre-implantation genetic screening (PGT) on treatment outcomes and birthweight.

Public benefit statement

The study aims to clarify the trends in birthweight over time and ascertain whether the growth of babies still differs from that of naturally-conceived babies and the impact of embryo freezing. The differences in birthweight are small and most ART babies are as healthy as naturally-conceived babies, but there is the potential for longer-term health issues if babies grow differently before birth.

Demonstrating the extent of the non-consent and its impact on the availability of data for research projects and the subsequent estimates of treatment outcomes is expected to lead to an understanding of the biases and better analyses of the data. Raising awareness of the issues is likely to lead to an increase in awareness of the value of consent amongst clinicians and patients and a consequent increase in consent rate.

The use of PGT as a treatment add-on is controversial as the effect of the add-on is often inadequately calculated, leading to incorrect estimates (including that derived from the HFEA register). A careful analysis is expected to show that the real-world data does reflect the results of clinical trials which show no benefit of PGT in treatment success rates and also shed light on any benefits there may be in reducing miscarriage.

Review date: 7 May 2026