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Prolonged Effects of Assisted reproductive technologies on the health of women and their children: a Record Linkage study for England (PEARL)


Study Status

The study team are now analysing the bespoke linked dataset. Watch the space for news about our results!

PEARL News and findings so far…

October 2023 – New results have been published in Human Reproduction, which describe the use and costs of primary care health services and hospital admissions. We report that children born after fertility treatment have higher hospital costs in their first year of life than children born to women who experienced no fertility problems. However, there were differences in the costs associated with GP care or hospital admissions after 12 months of age.

June 2023 – Assoc Prof Claire Carson has presented findings from the PEARL study at the 36th Annual Meeting of the Society for Pediatric Epidemiologic Research, Portland, Oregon, USA. Children born after subfertility were more likely to have an Autism diagnosis than those born to women with no recorded fertility problems, while IVF/ICSI babies had a similar but not statistically significant risk. ADHD was higher in those born after any ART, suggesting an association with treatment not explained by underlying parental subfertility.

What is the PEARL study trying to do?

PEARL is a large study of women and children in England. It will include babies born between 1991 and 2018, and their mothers. The study has three aims, these are:

  1. To find out the effect of fertility problems and fertility treatment on the health and development of ART children to adolescence
  2. To look at the impact of successful fertility treatment on the health and wellbeing of women who underwent treatment
  3. To estimate the additional costs to the NHS (if any) of caring for women and their children after successful fertility treatment

Why are we doing this study?

In general, most children born after the use of fertility treatment (such as IVF) are healthy. However, there is a small increase in the number of children who are born early, have a low birthweight, and who have health or developmental problems. We know less about the health of children born after fertility treatment as they grow up, as long-term follow-up studies are costly and time consuming. As a result, many studies are not big enough to detect small differences between the groups – which is important because the effects of fertility treatment on health may be subtle. We also need more evidence about the long term health of women who have had fertility treatment.

Who is doing this study?

PEARL is led by Dr Claire Carson, a Senior Researcher based at the National Perinatal Epidemiology in the Nuffield Department of Population Health at the University of Oxford. The study team includes Prof Jenny Kurinczuk, Prof Maria Quigley, Dr Oliver Rivero-Arias, Dr Clare Bankhead and Dr Sarah Lay-Flurrie.

How will we do the study?

PEARL will include about 270,000 mothers and their children. The information we use will come from over 20 years of existing health records. There are three different sources:

  • Records of fertility treatments held by the Human Fertilisation and Embryology Authority (for more details about the HFEA data see Box 1)
  • Health records from GP practices in England held by the Clinical Practice Research Datalink (for more details about the CPRD data see Box 2)
  • Records of any hospital care (for details of hospital data see Box 2)

The information from these three sources will be linked together by NHS-Digital who are experts in record linkage and work under strict data security regulations. After the information has been linked together, all the personal identifiable information such as names, NHS number and date of birth, will be removed. The information sent to the PEARL study team at the University of Oxford will not contain any of these personal identifiers and so it will not be possible to identify the individuals woman or child whose information is included. We will use this data to find out about the health of women and their children, and to see if there is any difference between those who had fertility treatment and those who didn't.

How do you know if you have been included in this study?

If you are a woman who has contributed data to the CPRD and you have had a baby between 1991 and 2018 could be included in this study. If you have had a baby after fertility treatment in the UK since 1991 your fertility records may also be used in this study (unless you specifically asked for them not to be). The research team cannot tell you if your information is being used for this research, as we do not have any names to allow us to identify individuals. Further information about opting out of research is outlined below.

Will you be able to choose whether to take part in the study? Can you decide if your child will be included?

It is not possible to ask all the people whose information will be included in this study if they want to take part (over 170,000 children have been born to people on the HFEA register since 1991). However, to use these data we need to have special permission to access and link data without consent. See Box 3 for more details about the use of your data in research.

Can you opt out? Can you choose to opt out of your child being included in PEARL?

If you are included in the PEARL dataset because your information is held on the HFEA register of fertility treatment then you can opt out of this study for the next six months (opt out ends 1st March 2021). If you have had fertility treatment in the UK and you do not want HFEA Register data for you or your child to be included in PEARL you will need to contact the clinic where you had treatment and request that they change your consent to research. More details for opting out of HFEA data use can be found in Box 3.

If you are included in the PEARL dataset because you are contributing for information to the CPRD via your GP practice you will not be able to opt out of PEARL once the data has been released to the research team. More information about contributing your data to the CPRD, including how to opt out of future studies should you wish to, can be found in Box 3.

One strength of this study is that it includes very large numbers of mothers and babies, and that it has long-term follow up data on these people. Before September 2009 the HFEA did not ask people whether they would consent to data linkage. It is not possible to go back to all the individuals who had fertility treatment between 1991 and September 2009 and ask for their consent now, but we need to use all the information on children born since 1991 to give us a complete picture and properly answer important research questions. The special permission (see Box 4) we have to use the data without consent is only given because the research we are doing can provide important information that would be very hard to get in any other way.

What will we do with your data?

First, different data sources will be linked together to create one large 'dataset' that includes all the information we need to conduct our research: Information from the HFEA register (about fertility treatment) will be sent to NHS-Digital, who are specialists in record linkage. They will use the names, dates of birth and other personal identifiers to add NHS number to all the records on the register. Then they will use NHS number to link this data to the NHS number of the people who contribute data to the CPRD, this will allow NHS-Digital to create a 'bridging file' which can be used to join the datasets together. NHS-Digital will not release any personal identifiable information to the research team, CPRD or HFEA. The bridging file will be used to create a special linked dataset for the study, combining HFEA register data and information from the CPRD, which will not contain any personal identifiable information. This linked data will be securely transferred to the research team at the University of Oxford. We will store the information securely and ensure that only the research team have access to the data.

Then, we will use this linked data (without any personal identifiers such as name, date of birth or NHS number) to conduct statistical analyses to help answer the study research questions. We hope that this will help us to find out more about children's health after fertility treatment, the wellbeing of women and whether there are any longer term costs to the NHS associated with fertility treatment.

Will we share your data?

No, due to the strict rules under which the PEARL study team have access to these data we cannot share the dataset with other researchers or other third parties. The PEARL dataset will not be shared, and will be stored and processed by the joint data controllers and processors (CPRD, HFEA and University of Oxford, and NHS-Digital, who will link the data) only.

How long will we keep your data for?

The PEARL dataset will be preserved until 2027, so that it is available for 5 years after the end of the study for the purposes of checking our analyses and publishing findings. It will continue to be stored electronically on secure servers at the University of Oxford until 2027.

What are your rights under GDPR (General Data Protection Regulations) with respect to the data in the PEARL study dataset?

The minimum personally-identifiable information possible will be used during the linkage process, and the dataset provided to the research team will not include details that allow individuals to be identified. Your rights to access, change or move your information are limited, as the dataset does not contain names, dates of birth or other personal identifiers so the research team cannot tell whether you are included.

What will happen to the results of PEARL?

The results of the study will be published in scientific conferences. There will be links to our publications here on the PEARL website, where we will also publish a summary of our results.

The results will also be made available to professionals and organisations who treat women with fertility problems, and who provide health services for women and children. For example, the results will provide information about:

  • What type of health problems or difficulties children born after fertility treatment might have as they grow up or indeed confirm that they do not have any particular problems.
  • Whether or not women who have had fertility treatment are more likely to experience depression or anxiety.

The results on the longer term costs of fertility treatment will be useful for the organisations who plan and provide fertility and health services – helping to ensure that women and children who need additional support receive it.

Who is responsible for the PEARL study dataset?

The PEARL dataset, which is a new bespoke dataset created only for this study, is the joint responsibility of the original data holders (Clinical Practice Research Datalink and Human Fertilisation and Embryology Authority), and the University of Oxford (who proposed the study and will conduct the research) – they are considered 'Joint Data Controllers'. The data will be stored securely at the University of Oxford. Study security measures are kept under review and refer to University Security Policies to keep up to date with current best practice. Please read Oxford University's data protection policy.

Who is funding this study?

The study is funded by the UK Medical Research Council as part of fellowship to Dr Claire Carson.

If you have questions about your fertility treatment or health, who can you contact?

If you have had fertility treatment, and you have questions about your health or that of your child, you can contact:

  • Your GP
  • The clinic where you received treatment
  • Fertility Network UK, a charity supporting those who experience infertility and fertility treatment. Their support number is: 0121 323 5025. View the Fertility Network UK website for more useful information.

If you want to know more about PEARL, who can you contact?

Please contact Dr Claire Carson, who leads this project. You can email her at or telephone (01865) 289755.

If you have a complaint, who can you contact?

If you wish to raise a complaint on how your personal data have been handled, you can contact the Data Protection Officers for the groups that look after and use your personal data as part of this research. These are:

Human Fertilisation and Embryology Authority (HFEA) – The Data Protection Officer for HFEA is Mr David Thomson. He can be contacted on: 020 7269 1900, or by email on:

Clinical Practice Research Datalink (CPRD) – The CPRD are part of the Medicines and Healthcare products Regulatory Agency, and their Data Protection Officer can be emailed at:, or you can write to them at: Data Protection Officer, MHRA, 10 South Colonnade, London, E14 4PU

The University of Oxford will not receive your personal identifiable data, as the final linked dataset will have this information removed. However, if you wish to speak to the University about the study please contact the study lead Dr Claire Carson on (01865) 289755 or email Alternatively, you may contact the University of Oxford Clinical Trials and Research Governance office on (01865) 572224 or by email:

If you are not satisfied with our response or believe we are processing your personal data in a way that is not lawful you can complain to the Information Commissioner's Office (ICO).

Box 1: Fertility data held by the HFEA

The information about fertility treatment comes from the Human Fertilisation and Embryology Authority who have kept a register of all fertility treatment in the UK since 1991. This contains details of the patients treated, their diagnoses, the type of treatment that they have received, pregnancies and births. Further information on the data that the HFEA hold, and how it is used and safeguarded can be found on the HFEA website.

Box 2: Data about health held by the CPRD

The main dataset comes from Clinical Practice Research Datalink (CPRD) GOLD dataset. General Practices (doctors' surgeries) have been selected across the UK, and within these practices information collected by the GP is available for research. The CPRD GOLD started in 1987 and now covers around 8% of the UK population. The information that is collected includes details of consultations, diagnoses, referrals, prescriptions and immunisations. Information about hospital admissions is also available for the people who are included in the CPRD GOLD dataset. Further details on the data that the CPRD hold, and how it is used can be found on the CPRD website.

The research team at the University of Oxford will not have access to your personal identifiable information, such as name, date of birth or NHS number. This means that we cannot identify individuals in the dataset. As such, we cannot tell you if your information is included, and we cannot send your information, amend or remove your information. However, if your data is included on the HFEA register there is an 'opt-out window' until 1st March 2021, which means you can contact the clinic where you had treatment and ask to change your consent to research. If your clinic has ceased operations since your treatment, you can contact the HFEA you wish to be removed from future research using your HFEA data, or data collected by the GP practice you can do so. Instructions are below:

Consent for the HFEA fertility data - Since September 2009, the HFEA have asked patients for consent to allow their HFEA data to be used in studies like this one, and after September 2009 only those people who gave their consent will be included in the PEARL study. Prior to September 2009, people undergoing fertility treatment were not asked if their data could be used in research, so we need special permission from the HFEA and the Confidentiality Advisory Group (part of the NHS Health Research Authority) to use the information in the HFEA register collected before September 2009 in our study (see Box 4) for further information about the legal basis for data use). If you have had fertility treatment and want to find out more about how the HFEA use your data, including how to contact them and opt out of this or future studies, please visit the HFEA website. There is a six month window to opt out of the PEARL study, which ends 1st March 2021, after which the dataset cannot be changed.

Consent for the health data – CPRD are legally allowed to access anonymised patient data. They offer patients the right to opt out from the use of their anonymised data, if they wish. GP practices that are part of the CPRD data system can mark your data as 'not to be used', even in an anonymised form, for CPRD research projects. Over the last 9 years very, very few patients decide not to let their anonymised data be used for what are very important public health reasons - improved, effective and safe treatments. If you are included in the CPRD data when it is released to the research team you will not be able to opt out of the PEARL study. However, if you want to opt out of providing data via the CPRD you can do so by speaking to your GP practice.

Additional opt-out from NHS-Digital - Anyone who has contacted their GP and stated that no identifiable data about them should leave the GP practice (type 1 objection) or have indicated that they want to opt out of identifiable information about them leaving NHS-Digital for purposes beyond direct care (type 2 objection) are excluded from data released by NHS-Digital. If you want to opt out of data release, you can do so by speaking to your GP practice.

1. Under Section 251 of the NHS Act 2006, we have permission to conduct this study without consent

We have special permission to conduct the PEARL study without study-specific consent (i.e. link, transfer, process and analyse the data) from the Confidential Advisory Group. This permission is given under Section 251 of the National Health Service Act 2006 and its current regulations, the Health Service (Control of Patient Information Regulations 2002) (CAG reference number: 16/CAG/0053).

2. Under the HFE Act (1990, amended 2008) we have permission to transfer, process and use the fertility register data for this study

We have permission from the HFEA's Register Research Panel to conduct this research. This means that release and flow of personal identifiable information from HFEA register to NHS-Digital is made under Regulation 3 of Human Fertilisation and Embryology (Disclosure of Information for Research purposes) Regulations (2010) (which were made under Section 33D, Human Fertilisation and Embryology Act, 2010, amended 2008). The processing of HFEA personal identifiable information by NHS-Digital to add NHS number is considered an outsourced function of the HFEA, so that the legal basis is Section 8D (1990 HFE Act, amended 2008).

3. Informed consent for HFEA register data collected after 2009

For data collected by the HFEA and recorded in the register after the introduction of consent in 2009, only those individuals who gave signed consent will be included in this study. For individuals who were not asked for consent (i.e. they had treatment prior to the introduction of consent in 2009), the legal basis is outlined in 1) and 2) above.

4. Data storage, processing and use complies with the General Data Protection Regulation

The legal basis for the processing and storage of personal data for PEARL is that it is 'a task in the public interest' (article 6(e)) and that sensitive personal data is necessary for archiving purposes in the public interest, scientific or historical research purposes or statistical purposes (article 9 (2) (j), based on Article 89(1)). This is particularly pertinent to the use of personal identifiers for the linkage by NHS-Digital. The dataset released to the research team is 'pseudonymised', meaning that we have no access to personal/sensitive personal data such as name, date of birth or NHS number.

Updated: Tuesday, 12 December 2023 15:39 (v44)


Principal Investigator

Claire Carson
Senior Researcher in Epidemiology University of Oxford