An "unprecedented view" of how the body changes during and after pregnancy has revealed many long-lasting impacts on the liver, kidneys and more, said scientists, and contradicted theories that “everyone is completely back to normal” six to eight weeks after birth.
Their findings provide the most detailed picture yet of how being pregnant affects the blood, organs and immune system on a weekly basis, which could help provide treatments post-pregnancy, and reveal the risks of developing certain conditions while pregnant.
The team was given an illuminating view of how the mother’s body changes week by week – to compensate for the incredible load on it – and how long it takes to recover after delivery, said Uri Alon at the Weizmann Institute of Science in Rehovot, Israel.
Despite its importance, pregnancy has been understudied, he added. For example, previous research has tracked how around 20 blood markers, like salt and iron levels, will change in dozens of women during pregnancy up to roughly six weeks after delivery, using samples taken during standard healthcare.
“These experiments are usually done on a small number of patients, and sample just once every trimester or one time point after delivery,” he told New Scientist.
To get a more comprehensive view, Alon and his colleagues analysed blood samples previously collected from more than 160 000 women in Israel, aged between 25 and 31, who collectively had more than 300 000 pregnancies.
Together, these samples provided a snapshot of the body each week from 20 weeks before conception to 18 months after delivery, with each woman providing data for a few points in time.
This approach gives useful insights into how the body generally changes during pregnancy at a population level, though tracking the same women at every time point would provide a better picture of individual trajectories, said Christoph Lees at Imperial College London.
The researchers mapped out changes in 76 blood markers, such as the levels of proteins, fats and salts, that indicate the function of the liver, kidneys, blood, muscles, bones and immune system.
They found that each of these markers varied widely from pre-conception levels during pregnancy, before either gradually returning to pre-pregnancy levels or overshooting the other way before settling back to the pre-pregnancy baseline.
Notably, they found that while 36 of the markers, including those related to blood clotting, bounced back within a month after delivery, 31 markers took more than 10 weeks to recover.
For instance, some changes to the liver and immune system took around five months to return to pre-pregnancy levels, and several kidney markers took roughly half a year, according to their findings, which were published in Science Advances. Some bone and muscle markers took even longer.
What exactly this means for women’s health is unclear, but it should be explored in future work, Alon said.
What’s more, a few other markers never returned to baseline levels, even more than a year after birth. “The slightly old-fashioned view that by six or eight weeks after pregnancy, everyone’s completely back to normal, is clearly wrong,” said Lees.
For instance, iron levels remained low long after giving birth. “Women are quite likely to be anaemic after delivery because of haemorrhaging, and because a developing foetus takes a lot of the iron stores out of their bodies. We typically think it takes six to 12 months for iron stores to get back to normal – this suggests it might take even longer.”
Meanwhile, levels of a protein called CRP stayed high. “CRP is affected by a number of different processes, certainly inflammation is one of them, but things like hormonal changes can also affect this”, he added.
In another analysis, the team looked at markers in women who had pre-eclampsia, which can lead to fatal complications for both mother and baby if left untreated. This revealed that, before conception, women who developed pre-eclampsia had elevated levels of blood cell fragments called platelets and a protein called ALT than those who did not develop the condition.
“For decades, the idea has been that the placenta doesn’t implant properly, and if it doesn’t implant properly, the blood supply is disrupted, it releases hormones and substances that lead to the mother getting high blood pressure,” Lees said.
“But some studies suggest that those who develop it have a different cardiovascular function before pregnancy – these findings add weight to this theory.”
If further studies show that these pre-conception markers really do indicate the risk of pre-eclampsia, they could potentially be used to pinpoint women at high risk.
“Then you could target them with ways of improving health prior to pregnancy, either through exercise and lifestyle advice, to lower their risk,” he said.
Study details
Pregnancy and postpartum dynamics revealed by millions of lab tests
Alon Bar, Ron Moran, Netta Mendelsohn-Cohen et al.
Published in Science Advances on 26 March 2025
Abstract
Pregnancy and delivery involve dynamic alterations in many physiological systems. However, the physiological dynamics during pregnancy and after delivery have not been systematically analysed at high temporal resolution in a large human population. Here, we present the dynamics of 76 lab tests based on a cross-sectional analysis of 44 million measurements from over 300 000 pregnancies. We analysed each test at weekly intervals from 20 weeks’ preconception to 80 weeks postpartum, providing detailed temporal profiles. About half of the tests take 3 months to a year to return to baseline postpartum, highlighting the physiological load of childbirth. The precision of the data revealed effects of preconception supplements, overshoots after delivery and intricate temporal responses to changes in blood volume and renal filtration rate. Pregnancy complications—gestational diabetes, preeclampsia, and postpartum haemorrhage—showed distinct dynamical changes. These results provide a comprehensive dynamic portrait of the systems physiology of pregnancy.
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