A cheap daily tablet can buy a baby extra weeks in the womb — if the offer is ever made

What four recent studies show about who is offered aspirin in pregnancy, when it should start, and whether it is actually taken

Pre-eclampsia is a pregnancy complication that can force a baby to be born weeks earlier than planned, and a daily low-dose aspirin tablet started early in pregnancy is the one treatment shown to push that moment later. Four studies published in 2025 and 2026 looked at who gets offered that tablet, when it should start, and whether it is actually taken. Together they suggest the medicine is working better than the system meant to deliver it.

What pre-eclampsia is, and why it is watched for so early

Pre-eclampsia is a condition of pregnancy in which a mother's blood pressure rises and other organs — kidneys, liver, sometimes the blood-clotting system — begin to struggle. It usually appears after 20 weeks of pregnancy, but its roots are laid down much earlier, in the first few months, when the placenta is building its connections to the wall of the womb. If those connections form poorly, the placenta never delivers blood as generously as it should. The mother's body responds with rising blood pressure; the baby may grow slowly. Around three to five in every hundred pregnancies are affected [1], [2].

There is no cure except delivery. That is why pre-eclampsia matters so much to newborn care: when it becomes severe, the only way to protect the mother is to end the pregnancy, and if that happens at 29 or 30 weeks, a baby who was healthy arrives extremely premature. A great many neonatal intensive care admissions begin this way.

How families used to face this, and what changed

For most of the twentieth century there was nothing to offer in advance. Families learned about pre-eclampsia when it arrived — a blood pressure reading at a routine visit, a sudden admission, a delivery brought forward by days or hours. Doctors could monitor and could deliver, but could not shift the odds beforehand.

Aspirin was first tried for this in the 1980s and 1990s, and the results were discouraging. Large studies gave it to broad groups of pregnant women and found only a small benefit, so for years it was regarded as barely worth the trouble. What eventually changed was not the drug but the way it was used. Researchers realised two things: that aspirin has to be started very early, while the placenta is still forming, and that it helps most in women already at genuinely high risk. When those two conditions were met, the picture transformed. In a trial called ASPRE — full name, the Combined Multimarker Screening and Randomized Patient Treatment with Aspirin for Evidence-based Preeclampsia Prevention trial — researchers screened almost 27,000 women at 13 hospitals in the United Kingdom, Spain, Italy, Belgium, Greece and Israel, identified the 11% at highest risk, and randomly assigned 1,776 of them to aspirin or a dummy tablet from around 12 weeks [3]. Early pre-eclampsia — the kind that forces delivery before 37 weeks — fell by 62%, and the most dangerous form, requiring delivery before 32 weeks, fell by almost 90%.

Countries disagree about who should be offered the tablet

There are two ways to decide who gets aspirin, and different countries have picked different ones.

The first is a checklist of risk factors: a previous pregnancy with pre-eclampsia, long-standing high blood pressure, diabetes, kidney or autoimmune disease, twins, a first pregnancy, a higher body weight, being over 35, and several more. The United States uses this approach, and its national advisory body has expanded the list over time to sixteen items [4], [5]. It is simple and needs no special test, but it is blunt: it now flags around 85% of pregnancies as candidates for at least considering aspirin [6], [7].

The second way combines a woman's history with three measurements taken at the 11-to-13-week scan — her blood pressure, a Doppler ultrasound of the arteries feeding the womb, and a blood test for a placental protein. A study called SPREE, run at seven UK hospitals, compared the two directly: for the same number of women flagged, the measurement-based method found 82 out of every 100 cases of early pre-eclampsia, while the checklist found 41 [8]. It is more accurate but costs more and needs equipment and trained staff [9], [10].

What the four newest studies found

The first, from an international team, looked specifically at women who already have high blood pressure before pregnancy — a group most guidelines say should simply all be given aspirin without further assessment. Pooling data on 51,024 pregnancies, the researchers found 556 such women, of whom about one in four developed pre-eclampsia [11]. Two results stood out. Earlier analyses of the ASPRE trial had suggested aspirin simply did not help this particular group [12]; the new work found that it did not stop pre-eclampsia, but pushed it later by an average of 3.6 weeks. And roughly one in five of these women turned out, on detailed assessment, to be at genuinely low risk — and among them, only one went on to develop early pre-eclampsia.

The second was a small trial at Beni-Suef University Hospitals in Egypt, which gave 45 high-risk women 75 mg of aspirin daily from before 12 weeks and compared them with 42 who did not receive it [13]. Pre-eclampsia occurred in 9% of the aspirin group against 29% of the others, and fewer babies were small, needed intensive care, or had serious newborn complications. The findings point the same way as everything else, but the trial was small, was not blinded, and contains several internal inconsistencies in its own reporting, so it is best read as encouraging rather than decisive.

The third is not a study but a practical tool: the Society for Maternal-Fetal Medicine, a professional body in the United States, published updated one-page checklists for clinicians and for patients [6]. Its reasoning is honest and telling — sixteen risk factors scattered across different parts of a medical record are simply not remembered reliably in a busy first appointment, and some are never asked about at all. Where checklists have been introduced, the proportion of eligible women correctly advised has risen substantially [14], [15].

The fourth asked the question the others assume. Researchers in Iceland surveyed 887 pregnant women [16]. Among those at high risk, 71% remembered being advised to take aspirin — meaning nearly a third did not. The gaps were worst for less familiar risk factors: 94% of women with long-standing high blood pressure recalled the advice, but only 12% of those with kidney disease. Once advised, though, women did take it. Only about 6% decided against it, and the most common reason for missing a dose was simply forgetting — not worry about harm.

What "delays it by three weeks" really means for a baby

It can sound like a modest result. It is not. A baby born at 29 weeks and a baby born at 32 weeks face substantially different journeys: different odds of needing a breathing tube, different feeding timelines, different lengths of stay, different long-term risks. Aspirin does not always prevent pre-eclampsia. What it often does is move the delivery later — and in prematurity, later is almost everything [17], [18], [19].

If you are pregnant, or planning to be

If you have any of the recognised risk factors, it is reasonable to ask directly at your first appointment whether aspirin is recommended for you. The dose is small — commonly 81 mg in North America, 150 mg in much of Europe — and guidance is to start it between 12 and 28 weeks, ideally before 16, and continue daily until delivery [6]. It is not the same as taking a painkiller dose of aspirin, and it has been studied extensively in pregnancy; the main documented downside is a small increase in minor bleeding [20].

Taking it consistently matters. Evidence suggests the protective effect depends on taking most of the doses, so it is worth building the tablet into a routine — with a prenatal vitamin, at a fixed time, with a phone reminder [21], [22], [23]. If you are not sure whether you have been assessed, asking is not a nuisance; the Icelandic survey suggests it is one of the most useful questions a patient can ask.

What researchers are working on next

Three questions are open. The first is whether the more accurate 11-to-13-week screening method is worth its cost in health systems that currently use checklists — and the Icelandic findings suggest the answer partly depends on fixing the simpler problem of making the recommendation at all [24]. The second is dose: whether a somewhat higher daily dose works better, and whether it is equally safe [25], [26]. The third is what else can be added, since aspirin does not appear to correct the underlying changes in a mother's circulation [27], and careful blood pressure treatment is a separate benefit in its own right [28].

For families already in a neonatal unit after an early delivery, In[Neo]Sight's coverage of monitoring babies who grow poorly before birth and steroid injections given before an early birth explains what happens in the steps that follow.

References

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