There has been a rise in the number of mistakes at UK fertility centres, with the wrong donor sperm resulting in a pregnancy in one case, a report says.

The mix-up happened at Simply Fertility in Chelmsford and led to a couple conceiving a child via a sperm donor they had not wanted, according to a report by the Human Fertilisation and Embryology Authority (HFEA).

The couple originally underwent fertility treatment in 2016 at the clinic using sperm from one donor but this was unsuccessful.

A second cycle using a different sperm donor worked and resulted in the birth of a child.

The couple then went back to the clinic in 2018 and asked to use the sperm again from the donor in the second cycle in order to give their child a full genetic sibling.

But because of a mix up with paperwork, sperm from the first unsuccessful treatment was used. The mistake was only realised after the embryo had been transferred to the woman.

The HFEA report said the senior management team at the centre was informed immediately, and the couple were invited to the centre where the error was explained, and an apology provided alongside the offer of further support.

The couple reported a positive pregnancy test and said they intended to continue with the pregnancy.

The clinic has since taken action to ensure such a mistake does not happen again.

A statement from the clinic said: “Simply Fertility has maintained an exceptionally high standard of service since it opened in 2013.

“Unfortunately, adverse incidents do sometimes occur. As a part of our investigation into this matter, we have identified how the mistake arose and we have put in place measures to ensure this does not happen again.

“We cannot discuss the details of the matter due to patient confidentiality but we have of course apologised sincerely for the distress caused to those concerned.”

The incident is detailed in a separate study published on Thursday from the HFEA which showed that mistakes are rare – affecting less than 1% of fertility treatment cycles – but have risen 6% over the last year and 18% in three years.

An increasing proportion of mistakes are serious, causing severe or moderate harm to patients.

Some of the increase is down to fertility clinics improving reporting of their errors, the HFEA said.

The data shows that, in 2018/19, there were 606 incidents, of which two were the most serious, grade A, and 294 were grade B.

The 606 is up 6% from 571 incidents the year before and an 18% rise from 514 in 2015/16.

Grade A incidents involve severe harm to one person, such as death or being implanted with the wrong embryo, or they involve major harm to many people, such as a frozen storage unit containing the embryos of many patients failing.

Grade B incidents involve serious harm to one person, such as the loss or damage of embryos, or moderate harm to many people, such as sensitive personal data about more than one patient being sent to the wrong recipient.

Some 56% of all grade A and B incidents reported to the HFEA are when something has clinically gone wrong.

In one grade A incident, the incorrect gas cylinder was delivered and connected, which damaged the embryos of several patients.

The HFEA said that, overall, it believes fertility treatment is becoming safer, with the quality of care improving across UK clinics.

Around 80% of clinics were issued with a full licence, confirming that most are meeting expected standards and performing well, it said.

The overall number of non-compliances per inspection has decreased each year since 2015/16 and over half of clinics had fewer areas of concern compared with their previous inspection.

Multiple births, the single biggest health risk from IVF, are also at an all-time low of 10%.

Overall, there were 351 non-compliances in 2018/19, down from 457 in 2015/16.

However, the HFEA said there was some room for improvement, with more non-compliances relating to medicines management being classed as major and critical.

There were 37 non-compliances in this area in 2018/19, of which six were critical and 24 were major, up from a total of 25 the year before.

On infection control, there were 25 in 2018/19, up from 15, and there were 11 non-compliances for legal parenthood, up from six.

Legal parenthood consent is essential to enable the patient’s partner to become the legal parent of any children.

Sally Cheshire, chairwoman of the HFEA, said: “I’m pleased that this report indicates continued good performance across the UK fertility sector.

“Significant improvements in some of the key areas we’ve highlighted previously with clinics are especially reassuring, proving that working together with clinics and the professional bodies is having a positive impact for patients.

“It’s good news that clinics have reduced the number of minor incidents, but we’re concerned that any incident is one too many.

“We will continue to ensure that the whole sector learns from any clinic incident, however minor, to understand what went wrong and, crucially, that steps are taken to ensure it does not happen again.”

Gwenda Burns, head of operations at Fertility Network, welcomed the report but said there was “room for improvement in these statistics”.