It takes more than a year for the postpartum body to settle to its new normal after giving birth – much longer than a three-month 'fourth trimester'.
That’s according to a recent study by biologists at the Weizmann Institute of Science and Helen Schneider Women’s Hospital in Israel, and Yale University School of Medicine in the US.
"Textbooks think of postpartum as six weeks but many experience a much longer recovery period," Prof Uri Alon, a systems biologist at Weizmann who led the research, told BBC Science Focus. "Knowing that recovery takes so long is important to focus research and attention on the year after delivery."
Using data from more than 300,000 Israeli births, the biologists studied how birthing bodies change from four and a half months before conception, to a year and a half after childbirth.
They gathered results from 76 different types of tests, measuring cholesterol, blood, immune cells, inflammation, the health of the liver, kidneys and bones – and so much more – among women who gave birth to healthy babies between 2003 and 2020.
This amounted to 44 million individual measurements: an enormous wealth of data that enabled the scientists to track how bodies changed on a week-by-week basis.
After all this, the biologists discovered that less than half – 47 per cent – of these test results stabilised within a month of delivery, including iron levels and blood clotting markers.
Another 12 per cent of health markers settled between four and 10 weeks after giving birth, and the remaining 41 per cent took more than 10 weeks to stop fluctuating.
The longest lag was a marker of bone and liver health, which took more than a year – 56 weeks – to stabilise after childbirth.
Plenty of other markers took many months to stabilise, including cholesterol, folic acid, red blood cells, and some markers of hormone and immune health.
“Data from these time points are rarely captured in cohort studies,” Prof Rebecca Reynolds, a metabolic medicine professor at the University of Edinburgh, told BBC Science Focus. Reynolds was not involved in this research.
“These data give us really important observations about the dynamic changes that occur [before and after pregnancy] and their time scale,” she said.
Several health measurements settled but didn’t return to pre-pregnancy levels even a year and a half after childbirth, including some markers of inflammation and blood health.
The researchers could not tell whether this was due to physical changes related to giving birth, or lifestyle and behaviour changes linked to the arrival of a baby.
But the scientists were able to find potential early signs or risk factors for several pregnancy disorders, including pre-eclampsia and gestational diabetes, which could help health professionals spot high-risk individuals before they become pregnant.
The study did not analyse the difference made by breastfeeding, which Prof Dimitrios Siassakos – an obstetrics and gynaecology professor at University College London – told BBC Science Focus was one of its limitations.
“[Breastfeeding] affects not just hormones and iron levels but may also be associated with infections such as mastitis,” he explained.
However, the study did create the most detailed picture yet of how the body changes after giving birth, which could help improve postpartum care.
Read more:
- Does having children actually make you happy? A neuroscientist explains
- Is it possible to be heavily pregnant and not realise?
- Why hasn't evolution made it pleasant to give birth?
About our experts:
Prof Uri Alon is a systems biologist at the Weizmann Institute of Science, principal investigator of the Uri Alon Lab and the Abisch-Frenkel Professorial Chair.
Prof Rebecca Reynolds is professor of metabolic medicine at the University of Edinburgh, UK. She is also the Personal Chair of Metabolic Medicine and Dean International at Edinburgh's College of Medicine & Veterinary Medicine, and the head of the Rebecca Reynolds Research Group. Her research focuses on understanding the mechanisms linking development in utero to health and disease across the lifespan.
Prof Dimitrios Siassakos is an honorary consultant in Obstetrics at University College London and University College Hospital. He is Chair of the Clinical Care Group of the International Stillbirth Alliance, Convenor for ROBUST operative birth courses across the UK, Vice Chair of the Intrapartum Care Clinical Study Group, and member of the National Institute for Health Research (NIHR) HTA prioritisation panel. He is lead author of several national and international guidelines, and Executive Editor for BJOG.
