Real-world data study reveals how pregnancy and childbirth reshape the body for over a year

A large real-world data (RWD) study published in Science Advances analyzed 44 million laboratory test results from more than 300,000 pregnancies in Israel, using routinely collected health records from the country’s largest healthcare provider, Clalit Health Services.

The study, titled ‘Pregnancy and postpartum dynamics revealed by millions of lab tests’, provides a comprehensive analysis of physiological changes throughout the reproductive timeline. The dataset used covers 140 weeks, spanning from 20 weeks before conception to 80 weeks after childbirth. Researchers evaluated 76 common blood and urine tests at weekly intervals to examine patterns associated with pregnancy and postpartum recovery in high chronological detail.

The results show that pregnancy affects nearly every major physiological system, including metabolism, immune response, liver and kidney function, and red blood cell health. While 47% of the tracked lab markers returned to pre-pregnancy levels within a month of childbirth, 41% took longer than 10 weeks to stabilize. Several markers, including liver enzymes (AST and ALT), cholesterol, and alkaline phosphatase (ALP), required 6 months to 1 year to return to baseline. About 12% of the tests returned to normal 1–10 weeks postpartum; however, some values, such as inflammation markers, thyroid function, and iron levels, did not return to preconception values even after 80 weeks.

“There’s a societal expectation that you bounce back quickly after childbirth,” said Jennifer Hall of University College London. “This is like the biological proof that you don’t.”

To focus on healthy pregnancies, the study included anonymized, aggregated data from women aged 20–35 who were not using medication or diagnosed with chronic illness. The researchers identified four main patterns in how test values changed over time: steady increases or decreases during pregnancy followed by gradual recovery, and more abrupt overshoots or undershoots at delivery. These sharper shifts may reflect compensatory mechanisms that persist even after the hormonal and metabolic influences of pregnancy end.

The study also identified changes that occurred even before conception. About a third of the tests showed significant trends in the preconception period, such as increased folic acid and decreased inflammation, likely related to positive health behaviors in preparation for pregnancy. Some of these early changes may have clinical relevance. In pregnancies affected by complications such as preeclampsia, gestational diabetes, and postpartum hemorrhage, several test markers deviated from healthy reference ranges before pregnancy began.

To investigate complications, the researchers analyzed test data from thousands of pregnancies affected by these conditions. In many cases, abnormal test values were observed not only during gestation but also before conception and after delivery. In gestational diabetes, for example, 17 out of 20 altered markers differed from healthy pregnancies during the preconception period alone. These findings suggest a potential role for earlier risk assessment and intervention than current clinical practices typically allow.

The researchers emphasize that this study addresses a significant gap in maternal health research, particularly for the postpartum period, which has often been studied at only a few time points. Instead of a brief 'fourth trimester', this dataset shows that nearly half of all tracked markers required 10–50 weeks to stabilize, indicating that the postpartum period is far longer than traditionally understood. As the authors note,

“We hope that the present dataset will lead to a better understanding of pregnancy and postpartum biology, and inspire similar studies of other crucial physiological processes that unfold over time.”