Human eggs that contain too many or too few chromosomes can lead to miscarriage, IVF failure and conditions such as Down’s syndrome. Now, researchers have found that giving the eggs a single injection can substantially reduce the problem. The approach could eventually boost the chances of success for older women undergoing IVF.

“It really seems like a big deal,” says at Nilo Frantz Reproductive Medicine in Porto Alegre, Brazil, who wasn’t involved in the new research. “To my knowledge, this is the first [therapy] to show such clinical potential for correcting this major cause of IVF failure.”

During a process called meiosis, egg and sperm cells eject exactly half of their genetic material. This means that when egg and sperm combine during fertilisation, they form an embryo with a complete genome. Sometimes, however, a sperm or egg cell has slightly more or slightly less than the half genome it should contain. This is a condition known as aneuploidy.

Aneuploidy affects about in the early 30s and becomes more common with age. “Already in the late 30s, more than 65 per cent of all eggs are aneuploid,” at Ovo Labs, a biotechnology company in Germany, told the audience at the conference in London on 6 July.

Clinicians sometimes screen IVF embryos for aneuploidy when treating couples at greater risk of miscarriage or IVF failure. , conditions caused by the genetic error – which include Down’s syndrome – are only detected via blood tests and ultrasound scans taken during the first trimester of pregnancy. Until now, there have been no ways to reduce the risk of aneuploidy occurring in the first place, says Zielinska.

Now, Zielinska and her colleagues have found that the level of a protein called shugoshin-1 is substantially lower in older mouse and human eggs than in younger ones. Shugoshin-1 helps with a stage of meiosis in which two copies of each chromosome line up along the middle of an immature egg cell. The protein maintains the molecular glue that holds each pair together.

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Upon fertilisation, the two copies of the chromosomes separate and move to opposite sides of the cell. One end ultimately forms the mature egg cell, and the other end is discarded.

But in older eggs, the glue holding the chromosome pairs together degrades, which can cause the two copies of each chromosome to separate before fertilisation. When this happens, the chromosomes spread unevenly throughout the cell – which means the resulting egg may be aneuploid.

To explore whether replenishing shugoshin-1 could prevent aneuploidy by helping to hold chromosome pairs together, the team collected 111 spare, immature eggs from more than 30 women aged between 22 and 43 who were banking eggs or undergoing IVF.

The team injected the genetic code for shugoshin-1, in the form of mRNA, into one or more of each donor’s eggs, and left other eggs from the same donor untreated.

A few hours later, chromosomes had prematurely separated in 53 per cent of the untreated eggs, whereas this figure was nearly half – 29 per cent – in the treated ones. In eggs from nine donors who were aged over 35, aneuploidy rates were 65 per cent, on average, in untreated eggs. But in treated eggs, the average figure was just 44 per cent. This reduction wasn’t statistically significant, although this is probably because of the study’s small sample size, according to the researchers.

Common IVF test misses some genetic abnormalities in embryos

Human embryos formed with in vitro fertilisation can develop genetic abnormalities in the time between genetic testing and implantation – though this may not affect their viability

Further experiments showed the approach could prevent aneuploidy in mouse eggs, which were then successfully fertilised to produce healthy offspring.

No side effects were seen in the mouse or human studies. “We’ve achieved live births in mice, so, from that perspective, we’re confident that this approach is not interfering in the mouse model with any steps of embryo development, and it doesn’t interfere with pup health and pregnancy health,” Zielinska told the conference audience.

The researchers are now working towards testing the effects of shugoshin-1 in people. This would involve tweaking standard IVF to use immature eggs rather than mature ones, but this change would be fairly easy to implement, says Zielinska.

She hopes the therapy, which the team calls EmbryoProtect, will provide an affordable way to improve IVF for older women. “We anticipate that the treatment will cost a fraction of the cost of a full IVF cycle,” says Zielinska. “By meaningfully improving IVF success rates, especially for women over 35 where baseline success is low, we hope that fewer attempts will be needed to conceive.”

On Monday, the US government announced two initiatives related to autism. It will update labelling on the common painkiller paracetamol, also called acetaminophen, warning use during pregnancy may increase the risk of autism and ADHD in children. It will also approve a drug called leucovorin for use in some children with autism spectrum disorder (ASD). Neither of these moves is based on robust scientific findings, and they are likely to have minimal effect on autism rates in the US.

The announcement comes after the country’s highest ranking public health official, Robert F Kennedy Jr, pledged in April to identify the causes of autism by the end of September. US President Donald Trump touted the initiatives as “historic steps to confront the crisis of autism” during a press conference.

This framing reveals either a misunderstanding or a misrepresentation of what we know about autism. There is no crisis – rates of autism began to increase rapidly in the 1980s as diagnostic criteria for the condition expanded. Over the past few decades, a higher level of awareness and recognition of the symptoms of autism has also contributed to an increase in autism diagnoses.

As for the cause of the condition, there is little evidence suggesting paracetamol is to blame. It is true multiple studies have suggested paracetamol use in pregnancy may increase the risk of autism in children. A of 46 studies found 27 of them identified a significant association between using paracetamol in pregnancy and children having a higher risk of neurodevelopmental conditions such as autism. But just because there is a relationship doesn’t mean paracetamol causes autism – other factors could be at play.

And there are conflicting findings from other studies. For example, a of nearly 2.5 million children found a slightly higher risk of autism in those exposed to paracetamol during pregnancy, but after comparing children exposed to the painkiller with those of their unexposed siblings, the effect disappeared. “It was the family history that mattered and not the use of paracetamol,” said at University College London in a press statement. “Research has shown that any apparent marginal increase [in autism] as a result of paracetamol in pregnancy tends to disappear when the analyses take into account the factors that matter the most”, such as genetics, which decades of research has indicated is a primary contributor to the condition.

During the press conference, Trump said pregnant women shouldn’t take paracetamol for pain or fever during pregnancy unless they “can’t tough it out”, and they “should talk to their doctors for more information”. However, the US Food and Drug Administration (FDA) acknowledged in a  a causal relationship between paracetamol and autism hasn’t been established and said in a paracetamol remains the safest widely available painkiller for use during pregnancy. “[It] is the only over-the-counter drug approved for use to treat fevers during pregnancy, and high fevers in pregnant women can pose a risk to their children,” the agency said. Fever during pregnancy has been linked to pre-term birth and in the fetus.

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The FDA also announced it will for people with cerebral folate deficiency, a condition that impairs uptake of vitamin B9 in the brain. Some research indicates upwards of of autistic people may also have this condition, which results in similar symptoms, including communication and sensory processing issues.

Leucovorin, a form of vitamin B9, is already available for treating deficiencies of this vitamin as well as side effects from certain cancer medications. Early evidence suggests it might improve some severe autism symptoms, too. For instance, a treated 23 autistic children with language impairments using two doses of leucovorin daily while a separate group of 25 children received a placebo. After 12 weeks, 65 per cent of children receiving leucovorin saw a clinically meaningful improvement in verbal communication compared with 24 per cent of those in the control group.

But so far, all of the studies on leucovorin and autism have been small, and most indicate only modest improvements. A larger clinical trial is underway, the . “Any evidence available at this point is exceptionally tentative and would not be considered robust,” said at Durham University in the UK in a press statement. “Whilst medications may help with very specific aspects [of autism], there is no medication or treatment that actively cures or erases autism.”

Following the announcement, the US Department of Health & Human Services clarified in a statement that “while promising, it is important to note that leucovorin is not a cure for ASD and may only lead to improvements in speech-related deficits for a subset of children with ASD”.

Kennedy, with Trump’s backing, has made tackling the “autism epidemic” a pillar of US public health policy. They both portrayed these policy changes as remarkable progress made in a short period of time. But the science suggests neither avoiding paracetamol in pregnancy nor taking leucovorin will significantly affect autism as Trump and Kennedy have claimed. Instead, the most likely outcome of these initiatives is they will sow confusion around how and when to safely treat pain or fever during pregnancy.