Baby girls exposed to paracetamol in the womb had 40% smaller ovaries. The study cannot say the drug caused it.

The stories

9 stories on this beat today.

Every story told the same way: what happened, who is involved, why it matters, how it works, the truth and the good news.

1. 01

   Baby girls exposed to paracetamol in the womb had 40% smaller ovaries. The study cannot say the drug caused it.

   40%

   smaller ovaries, on average, in three-month-old girls exposed to paracetamol in the womb

   Their wombs were 13% smaller and they had 23% fewer egg sacs. [1][2]

   302

   baby girls examined, born to 685 women followed from early pregnancy

   143 of the girls had not been exposed to the drug at all. [1][2]

   4,000mg

   the daily maximum dose, which no mother in the study went over

   Higher doses still went with bigger differences in the girls. [2]

   What happened

   • Researchers in Denmark examined 302 baby girls at about three months old.
   • Their mothers' use of paracetamol, the painkiller sold as Tylenol in the US, had been tracked through pregnancy. [1][2]
   • Paracetamol is the drug pregnant women take most often. [1]
   • Girls exposed in the womb had, on average, 40% smaller ovaries, 23% fewer follicles (the sacs that hold immature eggs) and 13% smaller wombs. [1][2]
   • Girls first exposed before week 17 of pregnancy also had less anti-Mullerian hormone, a hormone that signals how many eggs the ovaries hold and how good they are. [1]
   • Higher doses went with bigger differences, and no mother took more than the daily maximum of 4,000mg. [2]
   • Most of the mothers took it for headaches or muscle and joint pain, not for fever. [1][2]
   • In a second group of 1,210 girls born in Copenhagen between 1997 and 2002, exposure in the womb went with smaller ovaries in adolescence. [2]
   • The same group had smaller wombs at puberty. [1]
   • A girl is born with all the eggs she will ever have, so her egg supply is set before birth. [1]
   • Baby boys whose mothers took paracetamol had smaller testes on average, in a second paper accepted but not yet published. [2]
   • The study cannot prove the drug caused any of this.
   • The illness that led a mother to take it, or chance, could explain the link. [2]
   • Nobody can yet say whether these girls will have lower fertility or reach menopause earlier.
   • Finding out needs many years of follow-up. [1][2]
   • Guidelines still recommend paracetamol for pain and fever in pregnancy.
   • The study's leader says a high fever or severe pain left untreated carries its own risks. [1][2]

   Who is involved

   • Margit Bistrup Fischer a researcher at Copenhagen University Hospital-Rigshospitalet in Denmark; she led the study
   • Severine Mazaud-Guittot a researcher at INSERM, France's national health research institute; she says caution is wise, especially early in pregnancy
   • Dimitrios Siassakos a pregnancy specialist at University College London; he says the paper would not change his advice
   • Brian Lee a researcher at the University of Pennsylvania; he warns that sicker mothers, not the drug, may explain the link
   • Christian De Geyter a specialist in reproductive medicine at University Hospital Basel in Switzerland; he wrote that advice on the drug in pregnancy should be looked at again

   How it unfolded

   1. 1997-2002 1,210 girls are born in Copenhagen, and are later followed into their teens. [2]
   2. 2022 Research co-written by a French scientist shows paracetamol harms the growth of human ovary tissue kept in the lab. [2]
   3. 2025 Another study shows paracetamol affects the growth of human embryo cells. [2]
   4. 9 Sep 2026 The study of 302 baby girls is published in the journal Human Reproduction Open. [1]
   5. Not yet out A second paper, on the boys, has been accepted by the same journal. [2]

   Why it matters

   The next evidence is the paper on the boys, and whether anyone follows these girls to the age when their fertility can actually be measured. [2]

   The truth

   • What is really going on A Danish study found that baby girls exposed to paracetamol in the womb had smaller ovaries, and it cannot show the drug caused it. [1][2]The test that could show it would mean giving pregnant women the drug by chance, which the study's leader says would be unethical, so experts reading the same numbers disagree about whether advice to pregnant women should change. [2]
   • Why it works on people A figure like 40% smaller ovaries sounds like a verdict on a girl's future, but it was measured in babies at three months, and nobody can yet say what it means for fertility. [1][2]
   • Who pays Pregnant women in pain — Most other painkillers are not recommended in pregnancy because they can harm the baby, so they are left weighing one drug against mixed expert advice. [2]
   • Nobody knows yet

     Whether paracetamol caused the smaller ovaries at all.

     Mothers who take it may be sicker, have infections, eat differently or differ in their genes, and the team could not rule all of that out. [2] A trial that hands the drug out by chance would be unethical in pregnancy. [2]

   • Nobody knows yet

     Whether the girls will have lower fertility or an earlier menopause.

     The girls were measured at three months, and finding out needs follow-up into adult life, which the study's leader says is hard to do. [1][2]

   • Nobody knows yet

     Whether the result is partly chance.

     A UCL specialist says the team ran many analyses, which raises the odds of a chance finding. [2] The study's leader replies that correcting for that could hide a real effect. [2]

   • Nobody knows yet

     What the paper on the boys shows in detail.

     It has been accepted by the journal but not published, so only the headline finding of smaller testes is public. [2]

1. 02

   Cash from birth changed a DNA ageing test

   What happened

   • A US trial called Baby's First Years gave mothers on low incomes either $333 or $20 a month, decided by chance, starting shortly after their baby was born. [3]
   • The larger gift added about $4,000 a year, roughly 18% of family income. [3]
   • At age four, children in the $333 group scored slower on DunedinPACE, a DNA test on saliva that estimates how fast the body is ageing. [3]
   • The difference was small, and the mothers' own tests did not change. [3]

   Why it matters

   Because the gifts were handed out by chance, the difference comes from the money and not from other things that go with being poor. [3]

   The payments ended after each child's sixth birthday, and nobody knows yet whether the difference lasts or affects health. [3]

   How it works

   Why the same exposure can change a baby and leave the mother unchanged

   A body that is still being built can be changed by what reaches it, while a grown body has mostly finished building.

   The twist

   What reaches a mother can matter more for her child, because the child's body is still being built while hers is already finished.

   Step by step

   1. 1 A baby's organs are built in stages, many of them before birth
   2. 2 Whatever reaches an organ while it is forming can change how it forms
   3. 3 Some of what is built then is never added to later, like a girl's supply of eggs
   4. 4 A grown body finished those stages long ago
   5. 5 So one exposure can leave a mark on a child and little on the mother

   The same force, elsewhere today

   Where this chain is also running, in today's other stories.

   • Cash from birth changed a DNA ageing test

     Money paid to the mothers changed the four-year-olds' DNA test and not the mothers' own. The researchers call the first five years of life an especially sensitive time.

   • Sons make births harder in many mammals

     The idea is that a mother sends more energy to a son while he is forming in the womb, so he is born bigger.

   Where you've seen this

   Learning a language

   a child who hears it early picks up its sounds, while an adult who learns it later usually keeps an accent

   Wet concrete

   a stone pressed in while it is setting stays there for good, and the same stone on hard concrete just sits on top

   Tree rings

   a dry year makes a thin ring as the wood grows, and that ring stays for the rest of the tree's life

   The catch

   Timing only matters if the exposure does something: the Danish study cannot show paracetamol caused the change, and the cash trial does not yet know whether its difference lasts.

   And the whole of it

   Pregnant women, the doctors who write guidelines and the people deciding whether to give money to poor families all make choices that show up in a child's body years later. None of them can see those results on the day they choose.

   The truth

   • Who gains Children in low-income US families given $333 a month — At age four they scored slower on a DNA test of how fast the body is ageing than children whose families got $20. [3]
   • Nobody knows yet

     Whether the children's slower DNA ageing test lasts, or means better health.

     The payments ended after each child's sixth birthday, and the test was taken at age four, before any health effects could show. [3]

   Good news

   • In a US trial, children in low-income families given $333 a month from birth scored slower at age four on a DNA test of how fast the body is ageing than children whose families got $20.

1. 03

   Secret deals may shrink promised Medicare savings

   What happened

   • Medicare is the US government's health insurance for older people.
   • The Trump administration says tying what Medicare pays for drugs to 19 other rich countries would save $26 billion over several years. [4]
   • It is setting up two pilot schemes, GLOBE and GUARD.
   • They make drug companies pay extra rebates when a medicine costs more in the US than the lowest figure among those countries. [4]
   • A new analysis reported by STAT says confidential deals with more than two dozen drug companies could cut those savings by as much as 80%. [4]

   Why it matters

   If the analysis holds, Medicare would save far less on drugs than the Trump administration announced. [4]

   The detailed rules for both schemes are due shortly. [4]

   The truth

   • Who gains Drug companies that signed confidential price deals with the Trump administration — The GLOBE and GUARD schemes make companies pay rebates when US prices are higher than abroad, and the analysis says their deals could cut the resulting savings by as much as 80%. [4]
   • Who pays Medicare, the US government's health insurance for older people — The $26 billion it was told to expect from tying prices to other countries could shrink by as much as 80% because of the confidential deals. [4]
   • Nobody knows yet

     How much the secret drug-price deals really take out of Medicare's savings.

     The deal terms are confidential and the detailed rules for GLOBE and GUARD are not out yet. [4] We could read only the opening of STAT's report, so we do not know who did the analysis or how. [4]

2. 04

   1.9 million Britons' health data, checked for bias

   What happened

   • Our Future Health, a UK study that aims to sign up 5 million adults, has published a first look at 1.9 million of them in the journal Nature Medicine. [5]
   • More than 2.5 million people have registered since late 2022, making it the largest study of its kind. [5]
   • Its members broadly match the UK by age and sex, but only 13% come from the poorest fifth of areas, against 20% nationally. [5]
   • They reported more depression and anxiety than national figures, and fewer lung cancers. [5]

   Why it matters

   About 4.5% of the people invited agreed to join, so the authors say the study should not yet be used to work out how common diseases are across the country. [5]

   They also suggest long waits for NHS care, Britain's public health service, may have drawn in people with health problems that were not being treated. [5]

   The truth

   • Who gains Researchers who use Our Future Health — They get health data on more than 1.9 million consenting UK adults, the largest study of its kind. [5]
   • Who pays People in the poorest parts of the UK — They make up 13% of Our Future Health against 20% of the country, so findings from it may fit them least well. [5]
   • Nobody knows yet

     How much of Our Future Health's picture of disease comes from who chose to join.

     About 4.5% of the people invited signed up, and the authors think long NHS waits may have drawn in people with untreated health problems. [5]

   Good news

   • More than 2.5 million adults in the UK have signed up since late 2022 to give their health data to one study, Our Future Health.
3. 05

   Cancer treatment reshapes healthy gullet cells

   What happened

   • Scientists at the Wellcome Sanger Institute in England read the DNA of healthy gullet lining from 70 people who had surgery for gullet cancer. [6][7]
   • By age 60 to 70, almost every cell in a healthy gullet carries some mutations, and most never cause cancer. [6]
   • In patients given chemotherapy with radiation, cells with mutations in TP53, a gene that normally stops damaged cells growing, had spread further. [6][7]
   • After chemotherapy alone, cells with mutations that help them survive the drug 5-fluorouracil had spread. [6][7]

   Why it matters

   The team says a few weeks of treatment can change a pattern of cells in a healthy organ that took decades to form. [6]

   Reading healthy tissue like this could help explain why some patients get side effects from cancer drugs. [6]

   The truth

   • Nobody knows yet

     What the spreading mutant cells in treated gullets do next.

     The study read healthy tissue removed at surgery after treatment, and the reports we could read describe no later follow-up of those patients. [6][7]

4. 06

   Ancestry and diabetes, compared inside families

   What happened

   • Researchers used the Mexico City Prospective Study to ask whether differences between ancestry groups come from genes or from surroundings. [8]
   • They measured ancestry and 15 traits in 52,583 unrelated people and 39,714 relatives from 17,627 families. [8]
   • Comparing relatives removes the link between ancestry and home life that confuses comparisons between whole groups. [8]
   • Within families, more Indigenous American ancestry still went with shorter height and a higher risk of type 2 diabetes. [8]

   Why it matters

   Across the whole population, ancestry also went with years of schooling, but that link disappeared inside families. [8]

   That points to surroundings, not genes, as the cause of the schooling gap, and to a real genetic part in height and diabetes. [8]

5. 07

   India's newborn heart-defect deaths fall slowly

   What happened

   • About 9 in every 1,000 babies born in India have a heart defect, some 180,000 to 200,000 a year. [9]
   • A study in the journal Pediatric Research used Global Burden of Disease figures, a worldwide set of health estimates, from 1990 to 2021. [9]
   • India had about 1.5 million of the world's 8.6 million infant deaths from heart defects over those years. [9]
   • Newborn deaths from heart defects fell 1.5% a year in India, against 2.2% worldwide. [9]

   Why it matters

   Progress stalled from 2003 to 2013, then sped up nearly threefold from 2019 to 2021. [9]

   The authors put the economic loss from these deaths at $11.7 billion in 2021, and found large gaps in progress between parts of the country. [9]

   The truth

   • Who pays Families in India whose babies are born with heart defects — Newborn deaths from heart defects fell more slowly in India than worldwide, with an estimated economic loss of $11.7 billion in 2021. [9]
   • Nobody knows yet

     Why India's fall in newborn heart-defect deaths stalled from 2003 to 2013.

     The study reports the stall and the later speed-up, but the part we could read does not give a cause. [9]

   Good news

   • In India, the fall in deaths of newborn babies from heart defects stalled from 2003 to 2013. From 2019 to 2021 it sped up nearly threefold.
6. 08

   Sons make births harder in many mammals

   What happened

   • Nicole Grunstra of the University of Vienna and Jonathan Wells of University College London reviewed birth records for 140 mammal species. [10]
   • Difficult labour was more common with male babies in humans, cattle, water buffalo, sheep, goats, captive antelope and Asian elephants. [10]
   • Earlier work found mothers of boys in Nepal had an 18% higher chance of blocked labour. [10]
   • Their idea is that mothers send more energy to sons in the womb, so the babies grow bigger. [10]

   Why it matters

   About 700 people die giving birth every day around the world, and a baby's head too big for the birth canal is a leading cause. [10]

   The authors found little data on wild animals, and one outside scientist says they may be reading too much into what they found. [10]

   How it works

   The idea is that a mother sends more energy to a son while he is forming in the womb, so he is born bigger.

   The idea, in story 02: Why the same exposure can change a baby and leave the mother unchanged →

   The truth

   • Nobody knows yet

     Whether sons really made births harder over evolution.

     There is little data on wild animals, and a Harvard scientist says cases seen in the wild do not show a strong force. [10]

7. 09

   Europe offers 32 million euros for healthy-ageing research

   What happened

   • The European Innovation Council, an EU fund for risky new technology, is opening a 32 million euro call for research on healthy ageing. [11]
   • The money is meant for five to eight projects, each lasting five years. [11]
   • The EU expects the share of its people aged 85 and over to double from 3% to 6% by 2050. [11]
   • Lifespans have grown, but the years people live in good health have not grown as fast. [11]

   Why it matters

   The grants go to early ideas, meant to show that an approach to keeping people healthy for longer can work at all. [11]

   The truth

   • Who gains Scientists working on healthy ageing in Europe — The European Innovation Council is opening 32 million euros for five to eight five-year projects. [11]