- Pre-eclampsia is new high blood pressure in pregnancy, most likely from 20 weeks, often with protein in the urine; it can also start after birth (NHS). Its cause is not known (NHS causes page).
- Daily low-dose aspirin is the best-supported prevention. In the ASPRE trial of 1,776 high-risk women, 150 mg a day cut pre-eclampsia leading to birth before 37 weeks from 4.3% to 1.6% (odds ratio 0.38, 95% CI 0.20 to 0.74) (Rolnik et al., NEJM 2017). A Cochrane review of 77 trials found a smaller overall effect (the pre-eclampsia figure pools 60 of them): risk ratio 0.82 (0.77 to 0.88) (Duley et al. 2019).
- Treating blood pressure protects the mother from severe hypertension (risk ratio 0.49, 0.40 to 0.60) but has not been shown to prevent pre-eclampsia itself (Abalos et al., Cochrane 2018). In chronic hypertension, the US CHAP trial found treatment cut a composite of serious outcomes from 37.0% to 30.2% (adjusted risk ratio 0.82, 0.74 to 0.92) without more small babies (CHAP, NEJM 2022).
- Magnesium sulphate prevents seizures (eclampsia). In MAGPIE, 10,141 women with pre-eclampsia had 58% fewer fits (95% CI 40% to 71%), though 24% reported side effects versus 5% on placebo (Magpie Trial, Lancet 2002).
- The risk does not end at birth. Women with a hypertensive pregnancy had about 1.8 times the later risk of cardiovascular disease in a 73-study review (RR 1.80, 1.67 to 1.94) (Cardiology 2020 meta-analysis).
- Calcium supplements are less certain than older reviews suggested. The 2018 Cochrane review found a large effect with high-dose calcium (RR 0.45, 0.31 to 0.65), but a 2025 update, part-funded by the World Health Organization (WHO), found no clear benefit in the larger trials (RR 0.92, 0.79 to 1.05) (2018; 2025).
- Money trail: the core trials were publicly or charitably funded (EU and the Fetal Medicine Foundation, Canadian Institutes of Health Research, US NHLBI, UK Medical Research Council). The blood tests are different: the main sFlt-1/PlGF accuracy trial was funded by Roche Diagnostics (Zeisler et al., NEJM 2016), and the tests are sold by Roche, Thermo Fisher and QuidelOrtho.
- Evidence grade: Strong for magnesium sulphate against fits and for aspirin in high-risk women. Moderate for treating chronic hypertension and for PlGF testing. Weak for calcium outside low-intake settings.
Independent evidence review · Condition
High blood pressure in pregnancy ranges from a pre-existing condition to pre-eclampsia, a pregnancy-specific illness that can threaten mother and baby. The evidence is best for four things: low-dose aspirin for women at higher risk, blood pressure treatment for chronic hypertension, magnesium sulphate to prevent seizures, and planned follow-up after birth. Supplements and new blood tests are less settled. Our confidence is high for aspirin and magnesium sulphate, moderate for blood pressure targets and PlGF testing, and low for calcium. The core trials were publicly funded; the commercial money sits in diagnostic tests.
If you are pregnant, or gave birth in the last few weeks, and have a severe headache that simple painkillers do not ease, vision problems, pain just below the ribs, sudden swelling of the face, hands or feet, or you feel very unwell, contact your maternity unit straight away; if you cannot reach it after birth, the NHS advises calling 111 (NHS). A seizure, collapse or trouble breathing is an emergency: call your local emergency number. Do not start, stop or change aspirin, calcium or blood pressure medicine without advice from your midwife or doctor.
Table of contents
- Evidence summary
- What hypertension in pregnancy is
- Symptoms and red flags
- Causes and risk factors
- Treatments that work
- Medicines: aspirin, labetalol, nifedipine, methyldopa, magnesium sulphate
- Supplements and lifestyle claims
- Blood tests: PlGF and sFlt-1
- After birth and long-term heart risk
- Risks and harms of treatment
- Who to see
- Follow the money
- Related research
- Frequently asked questions
- Sources and funding notes
Evidence summary
| Claim | Evidence | Source | Funding / conflict | Strength |
|---|---|---|---|---|
| Low-dose aspirin prevents preterm pre-eclampsia in high-risk women | 1,776 women, 150 mg daily from 11 to 14 weeks to 36 weeks. Preterm pre-eclampsia 1.6% (13 women) vs 4.3% (35) with placebo; OR 0.38 (95% CI 0.20 to 0.74). | ASPRE, NEJM 2017 | European Union Seventh Framework Programme and the Fetal Medicine Foundation (a charity). Individual author declarations not opened. | Strong |
| Antiplatelet drugs (mostly aspirin) reduce pre-eclampsia across all risk levels | 77 trials in all; for proteinuric pre-eclampsia 60 trials, 36,716 women: RR 0.82 (0.77 to 0.88); preterm birth RR 0.91 (0.87 to 0.95); baby death RR 0.85 (0.76 to 0.95). Postpartum haemorrhage RR 1.06 (1.00 to 1.12); abruption RR 1.21 (0.95 to 1.54). | Duley et al., Cochrane 2019 | Medical Research Council listed as grant agency (no grant number in the record). | Strong (modest overall effect) |
| Treating mild-to-moderate hypertension lowers severe hypertension | 58 trials, 5,909 women. Severe hypertension RR 0.49 (0.40 to 0.60); pre-eclampsia adjusted RR 0.92 (0.75 to 1.14); small-for-gestational-age babies 0.96 (0.78 to 1.18). | Abalos et al., Cochrane 2018 | Medical Research Council grant G116/98. | Moderate |
| Treating mild chronic hypertension improves pregnancy outcomes | 2,408 women analysed. Composite of severe pre-eclampsia, birth before 35 weeks for medical reasons, abruption or baby death: 30.2% vs 37.0%; adjusted RR 0.82 (0.74 to 0.92). Small-for-gestational-age: RR 1.04 (0.82 to 1.31). | CHAP, NEJM 2022 | US National Heart, Lung, and Blood Institute (NIH). Disclosure forms not opened. | Moderate |
| Looser blood pressure control is a safe alternative | About 980 women with non-severe hypertension. Pregnancy loss or high-level neonatal care 31.4% (less tight) vs 30.7% (tight); adjusted OR 1.02 (0.77 to 1.35). Severe hypertension 40.6% vs 27.5%. Serious maternal complications 3.7% vs 2.0%, OR 1.74 (0.79 to 3.84). | CHIPS, NEJM 2015 | Canadian Institutes of Health Research (grant MCT 87522). | Moderate (tighter control favoured) |
| Magnesium sulphate prevents eclamptic fits | MAGPIE: 10,141 women, eclampsia down 58% (95% CI 40 to 71), 1.9% to 0.8%; maternal death RR 0.55 (0.26 to 1.14). Side effects 24% vs 5%. Cochrane: eclampsia RR 0.41 (0.29 to 0.58). | Magpie, Lancet 2002; Duley, Cochrane 2010 | Medical Research Council grant G116/98 appears on the Magpie follow-up papers and the Cochrane review record; we did not open the original funding line. | Strong |
| Calcium supplements prevent pre-eclampsia | 2018: high-dose (1 g or more daily) RR 0.45 (0.31 to 0.65), 13 trials. 2025 update: RR 0.83 (0.67 to 1.04), 6 trials, 15,364 women; large trials only RR 0.92 (0.79 to 1.05). | Hofmeyr 2018; Cluver 2025 | 2025 review "part-funded by the World Health Organization". 2018 record gives no support statement. | Weak (mixed) |
| sFlt-1/PlGF ratio helps rule out pre-eclampsia | Ratio 38 or lower: negative predictive value 99.3% (97.9 to 99.9). Above 38: positive predictive value 36.7% (28.4 to 45.7). | PROGNOSIS, NEJM 2016 | Funded by Roche Diagnostics (the test maker). | Moderate (industry-funded) |
| PlGF testing speeds diagnosis and may reduce severe maternal events | 1,023 eligible women, 11 UK units. Time to diagnosis 4.1 days (concealed) vs 1.9 days (revealed); severe maternal events 5% vs 4%, adjusted OR 0.32 (0.11 to 0.96). | PARROT, Lancet 2019 | National Institute for Health Research (UK). The test used was Alere (now Quidel) Triage; one co-author reported consulting fees from Alere. | Moderate |
| Hypertension in pregnancy raises later cardiovascular risk | 73 studies, over 13 million women: any cardiovascular disease RR 1.80 (1.67 to 1.94); heart failure 2.87 (2.14 to 3.85); stroke 1.72 (1.50 to 1.97); hypertension 3.16 (2.74 to 3.64). Older review: ischaemic heart disease RR 2.16 (1.86 to 2.52) after pre-eclampsia. | Cardiology 2020; Bellamy, BMJ 2007 | No funding information in the records we could open. A 2022 meta-analysis of 56 studies was funded by Thai public bodies (Medicine 2022). | Moderate (observational) |
Independent evidence and credibility scorecard
Independence tiers: 1 = regulator, guideline body or government body; 2 = academic, charity-funded or Cochrane team with no declared commercial funding for the work; 3 = independent authors with declared minor industry ties or industry-supplied tests; 4 = manufacturer-funded or manufacturer-authored. Credibility runs from A (highest) to D. Our sources cluster in the UK, with Canada, the US and the EU contributing the main trials; the UK Medical Research Council funded or supported several of the Cochrane reviews and the Magpie work, so the verdicts partly reflect one national research network.
| Source | Who funds it | Country | Independence tier (1–4) | Credibility (A–D) | Why it would tell the truth / residual bias |
|---|---|---|---|---|---|
| NICE NG133, hypertension in pregnancy | NICE is a UK public body (we did not open its funding page) | UK | 1 | A | Its reputation rests on transparent evidence review and cost-effectiveness. Residual bias: it relies on the same trials, and its site blocked us, so we read it through search extracts. |
| NICE PlGF diagnostics guidance (DG23, updated as DG49) | UK public body; assesses products from Roche, Thermo Fisher, QuidelOrtho and others | UK | 1 | A− | Judges tests on published accuracy and NHS cost. Residual bias: much of the accuracy data was produced or supplied by test makers. |
| WHO calcium recommendation (2018) | WHO: member-state dues under 20% of budget; over three-quarters is voluntary money from states, foundations and the private sector (WHO funding page) | Switzerland (intergovernmental) | 1 | B | Mandate is population health, and it must justify advice to many countries. Residual bias: donor-driven priorities; WHO also part-funded the 2025 calcium review. |
| ASPRE (Rolnik 2017) | European Union FP7; Fetal Medicine Foundation (charity) | Multi-country (EU-funded) | 2 | A− | Placebo-controlled and double-blind, so a false result would be exposed by repeat trials. Residual bias: the charity promotes the screening approach used in the trial. |
| Duley et al., Cochrane antiplatelet review 2019 | Medical Research Council listed | UK | 2 | A | Includes 77 trials (60 contribute to the pre-eclampsia result) and reports both benefits and bleeding signals. Residual bias: pooled trials vary in quality, and some are old. |
| CHIPS (Magee 2015) | Canadian Institutes of Health Research | Canada | 2 | B+ | Public funder with no product to sell. Residual bias: unblinded; researchers favoured the intervention they designed. |
| CHAP (Tita 2022) | US NHLBI (NIH) | US | 2 | A− | Large, public, pre-specified outcomes. Residual bias: unblinded; disclosure forms not opened. |
| Abalos et al., Cochrane antihypertensive review 2018 | Medical Research Council grant G116/98 | UK | 2 | B+ | Systematic, but many trials are old and small, so the drug-versus-drug evidence is weak. |
| Magpie Trial (Lancet 2002) | UK Medical Research Council (grant record on follow-up papers) | 33 countries (UK Medical Research Council funded) | 2 | A− | Large placebo-controlled trial; later Cochrane pooling agrees. Residual bias: original funding line not opened. |
| Cluver et al., Cochrane calcium review 2025 | Part-funded by the World Health Organization | International (Cochrane) | 2 | B+ | Updated evidence tempers earlier enthusiasm, which is a sign of honest correction. Residual bias: its funder also issues the calcium guideline. |
| PARROT (Duhig 2019) | NIHR (UK); Triage test from Alere, now Quidel (BJOG cost analysis) | UK | 3 | B | Real-world randomised design and public funding. Residual bias: a commercial kit under test, and one co-author declared Alere consulting fees in the follow-on paper. |
| PROGNOSIS (Zeisler 2016) | Roche Diagnostics, which sells the Elecsys test | Sponsor Roche (Switzerland); multinational trial | 4 | C | Prospective design with published confidence intervals. Residual bias: the sponsor profits if the test is adopted; we could not verify author conflicts. |
What hypertension in pregnancy is
Doctors usually separate three conditions. Chronic hypertension is high blood pressure that was present before pregnancy or appears before 20 weeks. Gestational hypertension is new high blood pressure after 20 weeks. Pre-eclampsia is new high blood pressure after 20 weeks together with protein in the urine or signs of other organs being affected (NHS). The NHS notes it is most likely from 20 weeks but can occur at any point, and sometimes begins in the days or weeks after birth. We could not open the terminology section of NICE NG133, so the exact definitions of chronic and gestational hypertension are standard usage rather than a quotation from the guideline.
The UK guideline is NICE NG133, published in June 2019 and updated in April 2023 on when to offer placental growth factor (PlGF) tests. It treats chronic hypertension with medicine when blood pressure is sustained at 140/90 mmHg or above, and sets a treatment target of 135/85 mmHg (read from a search extract of the recommendations).
Symptoms and red flags
High blood pressure and protein in the urine often cause no symptoms, which is why routine antenatal checks matter. Warning symptoms include a severe headache that simple painkillers do not ease, vision problems, pain below the ribs, sudden swelling of the face, hands or feet, persistent heartburn, vomiting and feeling very unwell (NHS). In CHIPS, severe hypertension meant a reading of 160/110 mmHg or higher, and it occurred in 40.6% of women managed with less-tight control against 27.5% with tight control (Magee et al. 2015).
Causes and risk factors
The NHS states plainly that it is not known what causes pre-eclampsia (NHS). Risk is higher with diabetes, existing high blood pressure, kidney disease, autoimmune conditions such as lupus or antiphospholipid syndrome, and pre-eclampsia in a previous pregnancy. Other factors are a first pregnancy, age 40 or over, Black or South Asian ethnic background, twins or more, a close relative with pre-eclampsia, 10 or more years since the last pregnancy, and a body mass index of 35 or more before pregnancy.
The blood-vessel signalling proteins PlGF and sFlt-1 are out of balance in many women with pre-eclampsia; that is the biological basis for the blood tests discussed below, and Roche describes the same imbalance in its own release (Roche release). That is a company statement, not an independent proof of mechanism.
Treatments that work
| Approach | What the best evidence shows | Verdict |
|---|---|---|
| Low-dose aspirin from early pregnancy | ASPRE odds ratio 0.38 for preterm pre-eclampsia in high-risk women; Cochrane RR 0.82 across trials. | Works |
| Antihypertensive medicine for chronic hypertension | CHAP adjusted RR 0.82 for serious composite outcome; Cochrane RR 0.49 for severe hypertension. | Works (for the mother; does not prevent pre-eclampsia) |
| Magnesium sulphate in pre-eclampsia | About 58% fewer fits in MAGPIE; RR 0.41 in Cochrane. | Works |
| Tight versus less-tight blood pressure control | CHIPS found no difference in the main outcome but more severe hypertension with less-tight control. | Mixed |
| Calcium supplements | Large effect in 2018 pooled results, much smaller and not significant in the 2025 update and large trials. | Mixed |
| PlGF-based testing | Good at ruling out in industry-funded PROGNOSIS; faster diagnosis in publicly funded PARROT. | Mixed |
| Delivery | The NHS describes birth as the main cure route, sometimes before 37 weeks, though there is no cure for the condition itself. | Works (timing is individual) |
Medicines: aspirin, labetalol, nifedipine, methyldopa, magnesium sulphate
Aspirin
NICE advises women at high risk (previous hypertensive disease in pregnancy, kidney disease, autoimmune disease, diabetes or chronic hypertension), and women with more than one moderate risk factor, to take 75 mg to 150 mg of aspirin daily from 12 weeks until birth (read from search extracts of NG133). The NHS says a midwife or GP may prescribe it and not to start it without advice (NHS). The trial dose in ASPRE was 150 mg (Rolnik 2017). These are doses studied and guideline doses, not personal instructions. In the Cochrane review, aspirin was linked to a small increase in postpartum haemorrhage (RR 1.06, 1.00 to 1.12) and an unclear change in placental abruption (RR 1.21, 0.95 to 1.54) (Duley 2019). We found no aspirin trial among our key sources funded by a drug maker.
Labetalol, nifedipine and methyldopa
For chronic hypertension, NICE says to consider labetalol first, nifedipine if labetalol is unsuitable, and methyldopa if both are unsuitable, choosing on side effects, fetal risks and preference. It also notes that some nifedipine brands were contraindicated in pregnancy by their manufacturers when the guideline was published (search extract of NG133). ACE inhibitors and angiotensin receptor blockers are stopped when pregnancy is confirmed. The sequence reflects side-effect profiles more than head-to-head trial wins. The Cochrane review shows that treatment versus no treatment lowers severe hypertension, but we did not verify a clear winner between the drugs from its abstract (Abalos 2018). A publicly funded NIHR trial, Giant PANDA, plans to randomise 2,300 women to nifedipine or labetalol strategies, which suggests the question is still open (protocol, Trials 2023). After birth, methyldopa should be stopped within two days and switched, and enalapril is the usual first choice, with a different plan for breastfeeding women (search extract of NICE postnatal advice; see below).
Magnesium sulphate
Magnesium sulphate is given in hospital for severe pre-eclampsia and eclampsia. MAGPIE randomised 10,141 women; eclampsia fell from 1.9% to 0.8% (58% lower, 95% CI 40% to 71%), maternal death was lower but not significantly (RR 0.55, 0.26 to 1.14), and 24% reported side effects versus 5% (Magpie 2002). At 18 months, death or disability in children was similar in the two groups (15.0% vs 14.1%, RR 1.06, 0.90 to 1.25) (BJOG 2007). We could not retrieve the NICE magnesium wording, so we do not give indications here.
Supplements and lifestyle claims
Calcium
WHO recommends 1.5 to 2.0 g of elemental calcium daily for pregnant women in populations with low dietary calcium to reduce pre-eclampsia, with moderate certainty (search extract of the WHO recommendation). The 2018 Cochrane review found a 55% lower risk with high-dose calcium (13 trials, 15,730 women) and also lower high blood pressure (RR 0.65, 0.53 to 0.81) (Hofmeyr 2018). The 2025 update included 6 trials and 15,364 women and found RR 0.83 (0.67 to 1.04), and RR 0.92 (0.79 to 1.05) when only large trials were counted (Cluver 2025). A reasonable reading is that calcium may help where diets are low in calcium, and that the benefit elsewhere is unproven. The NHS tells women not to start calcium or aspirin unless a midwife or GP advises it (NHS). A trial of calcium started before pregnancy found RR 0.80 (0.61 to 1.06) in a single trial of 633 women (Hofmeyr 2019).
Other claims
We did not review vitamins C and E, vitamin D, fish oil, exercise or salt restriction for this article and make no claim about them. Readers will find general blood pressure supplement evidence in our blood pressure supplements guide, which is not specific to pregnancy.
Blood tests: PlGF and sFlt-1
NICE first reviewed PlGF testing in 2016 (diagnostics guidance DG23), recommending two tests, the Triage PlGF test and the Elecsys sFlt-1/PlGF ratio, to help rule out pre-eclampsia. A 2024 update (DG49) recommends four tests, for people between 20 and 36 weeks and 6 days, and does not recommend the B.R.A.H.M.S Kryptor tests for routine NHS use (search extract of NICE DG49). In PROGNOSIS, a ratio of 38 or below had a negative predictive value of 99.3% (97.9% to 99.9%), meaning very few women with a low ratio went on to develop pre-eclampsia in the follow-up window, but a ratio above 38 had a positive predictive value of only 36.7%, so most women with a high ratio did not (Zeisler 2016; funded by Roche Diagnostics). In the NIHR-funded PARROT trial, revealed PlGF results shortened the median time to diagnosis from 4.1 to 1.9 days (time ratio 0.36, 0.15 to 0.87) and were linked to fewer severe maternal events (adjusted OR 0.32, 0.11 to 0.96), with no clear change in perinatal outcomes (Duhig 2019). Because this was a stepped-wedge design in 11 units, it is less clean than a standard placebo trial. NICE says PlGF tests should not be used to decide planned early birth in preterm pre-eclampsia, and that repeat testing needs more research (search extract).
After birth and long-term heart risk
Blood pressure often peaks in the first week after birth. NICE's postnatal advice, read from search extracts, includes checks at least four times a day in hospital for women with pre-eclampsia, daily checks for the first two days for chronic or gestational hypertension, at least one check 3 to 5 days after birth, a 6 to 8 week medical review, and a treatment target below 140/90 mmHg. The NHS adds that some women need blood pressure medicine for a few weeks (NHS).
Long-term risk is real but relative. A 2020 meta-analysis of 73 studies and over 13 million women found about 1.8 times the later risk of cardiovascular disease (RR 1.80, 1.67 to 1.94), 2.87 for heart failure and 3.16 for hypertension (Cardiology 2020). A 2022 review of 56 studies found the risk of later hypertension was highest in the first five years (RR 5.34, 2.74 to 10.39) (Medicine 2022). The older BMJ review reported RR 2.16 for ischaemic heart disease and 1.81 for stroke after pre-eclampsia (Bellamy 2007). These are observational findings and cannot prove that pregnancy causes the later disease; they may reflect shared risk. Absolute risks depend on age and follow-up time. For wider context see our guide to cardiovascular risk calculators.
Risks and harms of treatment
Untreated severe pre-eclampsia can cause seizures, stroke and death. Severe hypertension was the key outcome that treatment reduced in Cochrane pooled data (RR 0.49), and eclampsia fits fell by about 58% with magnesium sulphate. Treatment has its own trade-offs: magnesium sulphate side effects were reported by 24% of women in MAGPIE, and aspirin raised postpartum haemorrhage slightly. Lowering blood pressure too far is also a concern, which is why NICE suggests reducing treatment if pressure is sustained below 110/70 mmHg or symptoms of low pressure appear (search extract of NG133).
In CHAP, treatment did not increase small-for-gestational-age babies (RR 1.04, 0.82 to 1.31) (CHAP). In CHIPS, less-tight control had slightly more serious maternal complications (3.7% vs 2.0%), although the difference was not statistically significant (CHIPS).
Who to see
Routine antenatal checks with a midwife pick up most cases. Women with chronic hypertension, kidney disease, diabetes or earlier pre-eclampsia usually need specialist obstetric input. The NHS describes specialist review, more frequent appointments and scans, and hospital care for severe cases (NHS). Preconception review matters because some blood pressure medicines, including ACE inhibitors and angiotensin receptor blockers, are stopped in pregnancy; see losartan for one example. After birth, a GP review and long-term blood pressure checks are sensible.
Follow the money: who makes it and who funded the evidence
Who sells the tests and treatments
- Roche (Switzerland): sells the Elecsys sFlt-1/PlGF ratio. The US Food and Drug Administration has cleared it as a prognostic test for hospitalised women with hypertensive disorders, to sort them into low- and high-risk groups for severe pre-eclampsia within two weeks; Roche's product page describes the indication as aiding assessment of risk for pre-eclampsia with severe features within two weeks in women hospitalised between 23+0 and 34+6 weeks (Roche release). Roche Diagnostics funded the PROGNOSIS trial.
- Thermo Fisher Scientific (US): sells the B.R.A.H.M.S sFlt-1 and PlGF plus KRYPTOR tests. Its US label covers women hospitalised for hypertensive disorders between 23+0 and 34+6 weeks (Thermo Fisher product page). NICE did not recommend these tests for routine NHS use in its update. We could not verify the company's acquisition history of the B.R.A.H.M.S brand.
- QuidelOrtho (US): sells the Triage PlGF test, which it says is not for sale in the US (QuidelOrtho). Quidel acquired the Triage assets from Alere (the price and antitrust background could not be verified because the news page blocked us); it received Health Canada approval for the PlGF test in March 2024 (Business Wire).
- Aspirin, labetalol, nifedipine, methyldopa, magnesium sulphate and calcium: these are widely used older products, and we found no manufacturer-funded trial of them among our key sources. We did not trace manufacturers or market sizes.
Research funding at a glance
12 sources graded. The counts below are the independence tiers assigned in the scorecard above. They count sources, not funding amounts or evidence quality.
Public funding alone does not prove independence, and commercial funding alone does not prove a claim false. Named funders, countries and relationships are in the scorecard and source notes.
Who funded the trials
- Public and charity money: ASPRE was funded by the EU Seventh Framework Programme and the Fetal Medicine Foundation (Rolnik 2017); CHIPS by the Canadian Institutes of Health Research (Magee 2015); CHAP by the US NHLBI (Tita 2022); PARROT and Giant PANDA by the UK NIHR (Duhig 2019; Giant PANDA protocol). Several UK Cochrane reviews and the Magpie work list Medical Research Council grants.
- Industry money: PROGNOSIS was funded by Roche Diagnostics (Zeisler 2016). PARROT used a Quidel/Alere test and a co-author reported consulting fees from Alere in the cost-effectiveness paper (BJOG 2019).
- Funders of the funders: WHO gets under 20% of its money from member-state dues and over three-quarters from voluntary contributions, including from states, foundations and the private sector (WHO). WHO part-funded the 2025 calcium review and issues the calcium guideline, so the same organisation sits on both sides of that claim.
Documented integrity events and gaps
We did not find a regulatory ban, warning letter or recall relating to the tests or drugs discussed. We did not search for such events exhaustively. The main money-related issue we found is structural: the strongest sensitivity data for the Elecsys test come from a trial paid for by its maker, while the publicly funded trial used another company's kit.
Related research
For wider, evidence-graded context, see these Pure City Research guides:
- Heart disease during pregnancy
- Peripartum cardiomyopathy
- Hypertension
- Hypertensive emergency
- Blood pressure medicines
- Home blood pressure monitoring
- Aspirin
- Magnesium
- Gestational diabetes
- Chronic kidney disease and the heart
- Perinatal depression
Frequently asked questions
What is the difference between gestational hypertension and pre-eclampsia?
Gestational hypertension is new high blood pressure after 20 weeks; pre-eclampsia adds protein in the urine or signs that other organs are affected (NHS). Gestational hypertension can progress to pre-eclampsia, so both are monitored.
Does aspirin prevent pre-eclampsia?
In high-risk women it lowered preterm pre-eclampsia from 4.3% to 1.6% in ASPRE (OR 0.38) (Rolnik 2017). Across all antiplatelet trials the average effect was smaller, RR 0.82 (Cochrane 2019). It is prescribed on the basis of risk factors, not bought off the shelf.
Which blood pressure medicines are used in pregnancy?
NICE lists labetalol first, then nifedipine, then methyldopa, and stops ACE inhibitors and angiotensin receptor blockers when pregnancy is confirmed (search extract of NG133). The choice rests on side effects and individual circumstances.
Is it worth treating mild high blood pressure in pregnancy?
For chronic hypertension, the CHAP trial says yes: a lower rate of serious outcomes (adjusted RR 0.82, 0.74 to 0.92) without more small babies (CHAP). Cochrane pooled data show treatment lowers severe hypertension but not pre-eclampsia (Abalos 2018).
What does magnesium sulphate do?
It prevents seizures in women with pre-eclampsia. MAGPIE found 58% fewer fits, with side effects such as flushing reported more often (Magpie 2002).
Should I take calcium supplements?
The evidence is mixed. WHO recommends high-dose calcium in low-intake populations, while a 2025 Cochrane update found no clear benefit in larger trials (Cluver 2025). The NHS advises against starting calcium without clinical advice (NHS).
What is the PlGF blood test?
It measures placental growth factor, sometimes with sFlt-1, to help rule out pre-eclampsia in women with suspected disease. NICE has updated its recommendations since 2016 (DG49). The best accuracy figures came from a Roche-funded trial, and a UK public trial found faster diagnosis (PARROT).
Does pre-eclampsia raise the risk of heart disease later?
Yes, on average. A 73-study review found about 1.8 times the risk of cardiovascular disease (Cardiology 2020). The studies are observational, so they show association, not proof of cause.
Sources and funding notes
What we could not verify: the NICE website blocked automated access, so the NG133 and DG23/DG49 details are from search extracts, not from reading the pages; the NICE terminology section and its magnesium sulphate recommendations were not retrieved. The WHO calcium recommendation wording came from a search extract; the one WHO-related page we opened gave only its title and PICO questions, with an inconsistent date (2018 citation, 2025 listing), or any Cochrane funding page. Author conflict-of-interest statements for ASPRE, CHAP, CHIPS, MAGPIE and the meta-analyses were not opened; for the Cochrane and meta-analysis records, funding comes from the Europe PMC grant record or abstract. The original Magpie funding line was not seen. We could not confirm who funded the long-term cardiovascular meta-analyses from Europe PMC (the Medicine 2022 review lists Thai public funders). We did not verify the acquisition history of B.R.A.H.M.S by Thermo Fisher, the price of Quidel's purchase of the Triage assets, the date of Roche's FDA clearance or its analyser count, did not review vitamins, vitamin D, fish oil, exercise or salt, and did not confirm a head-to-head winner among labetalol, nifedipine and methyldopa.
- NICE NG133. Hypertension in pregnancy: diagnosis and management — UK guideline; read through search extracts; UK public body.
- NICE DG49 (replacing DG23). PlGF-based testing to help diagnose suspected preterm pre-eclampsia — UK diagnostics guidance; search extract only.
- NHS. Pre-eclampsia and causes — patient information; Crown copyright; reviewed 23 March 2026.
- WHO. Calcium supplementation during pregnancy for prevention of pre-eclampsia and its complications (2018) — guideline; WHO; wording from search extract, page opened gave title only. WHO funding — how WHO is financed.
- Rolnik et al. ASPRE. NEJM 2017 — aspirin trial; EU FP7 and Fetal Medicine Foundation.
- Duley et al. Antiplatelet agents for preventing pre-eclampsia. Cochrane 2019 — systematic review; Medical Research Council listed.
- Magee et al. CHIPS. NEJM 2015 — blood pressure control trial; Canadian Institutes of Health Research.
- Tita et al. CHAP. NEJM 2022 — chronic hypertension treatment trial; US NHLBI.
- Abalos et al. Antihypertensive drug therapy for mild to moderate hypertension during pregnancy. Cochrane 2018 — systematic review; Medical Research Council G116/98.
- Giant PANDA protocol. Trials 2023 — planned nifedipine versus labetalol trial; NIHR (protocol only; read via Europe PMC record).
- Magpie Trial. Lancet 2002 — magnesium sulphate trial; MRC grant on follow-up papers. Child outcomes at 18 months, BJOG 2007; Duley, Cochrane 2010 — MRC G116/98.
- Hofmeyr et al. Calcium supplementation. Cochrane 2018; Cluver et al. Cochrane 2025 — part-funded by WHO; Hofmeyr 2019, calcium before pregnancy — support not stated.
- Zeisler et al. PROGNOSIS. NEJM 2016 — sFlt-1/PlGF accuracy; funded by Roche Diagnostics.
- Duhig et al. PARROT. Lancet 2019 — PlGF testing trial; NIHR. Duhig et al. cost-effectiveness analysis, BJOG 2019 — NIHR; Triage test from Alere/Quidel; one consulting-fee declaration.
- Cardiology 2020 meta-analysis; Medicine 2022 meta-analysis — Thai public funders; Bellamy et al. BMJ 2007 — long-term risk; funding not in record.
- Roche. Elecsys sFlt-1/PlGF ratio FDA 510(k) clearance — company release; maker.
- Thermo Fisher. B.R.A.H.M.S PlGF plus KRYPTOR — company product page; maker.
- QuidelOrtho. Triage PlGF Test; Fierce Biotech. Quidel to buy Alere Triage assets; Business Wire, Health Canada approval — company and trade news.
Educational research reviewed 6 October 2026. This article is not medical advice; talk to a qualified clinician or pharmacist before starting, stopping or combining treatments.
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