VTE in Pregnancy: Prophylaxis and Treatment Decisions That Changed
Clinical Practice Update — Who needs heparin, at what dose, from when, and how to treat and deliver safely under ACOG and the 2026 RCOG interim guidance
This is an original clinical education article informed by current guidelines and evidence. See References below for source documents.
- Clinical Focus
- Risk assessment, LMWH thromboprophylaxis dosing, diagnosis, therapeutic anticoagulation, peripartum management and postpartum prophylaxis for VTE in pregnancy
- Target Audience
- Obstetricians, maternal-fetal medicine specialists, obstetric physicians, haematologists, anaesthetists, midwives, general practitioners, emergency physicians, residents
- Setting
- Primary care, early pregnancy units, antenatal clinics, emergency departments, labour ward, postnatal care
- Source Evidence
- •ACOG Practice Bulletin No. 196 — Thromboembolism in Pregnancy (Obstet Gynecol, 2018; reaffirmed 2025)
- •RCOG Green-top Guideline No. 37a — Reducing the Risk of VTE during Pregnancy and the Puerperium (2015) and RCOG Position Statement (September 2026)
- •RCOG Green-top Guideline No. 37b — Thrombosis and Embolism during Pregnancy and the Puerperium: Acute Management (2015)
- •NHS England Maternal Care Bundle, Element 1: Venous Thromboembolism (2026)
- •Highlow trial — Intermediate-dose vs low-dose LMWH after previous VTE (Lancet, 2022)
- •ASH 2018 Guidelines — VTE in the Context of Pregnancy (Blood Adv, 2018)
What Changed in Practice
VTE in pregnancy remains the leading direct cause of maternal death in the UK, and the guidance now pushes risk assessment earlier and heparin doses lower.4 ACOG’s Practice Bulletin, reaffirmed in 2025, still anchors US care, while RCOG issued interim amendments in September 2026 pending a full update.1,3
Key Clinical Takeaways
Direct actions for VTE in pregnancy, most practice-changing first.
- 1Screen for VTE risk at the very first contact with a positive pregnancy test and start LMWH within 72 hours for prior VTE, disabling hyperemesis, or BMI above 50 → Who Needs Prophylaxis for VTE in Pregnancy, and When?
- 2Prescribe fixed low-dose LMWH, not intermediate dosing, for women with a previous clot → Which LMWH Dose Should I Prescribe?
- 3Dose prophylactic LMWH by the revised weight bands, with enoxaparin 40 mg daily up to 100 kg → Which LMWH Dose Should I Prescribe?
- 4Start LMWH on admission for hyperemesis or immobility and continue for a week after it resolves → Who Needs Prophylaxis for VTE in Pregnancy, and When?
- 5Start therapeutic LMWH as soon as VTE is suspected, unless contraindicated, while imaging is arranged → How Should Acute VTE in Pregnancy Be Treated?
- 6Write the delivery and neuraxial plan by 36 weeks for every woman on LMWH → How Should Anticoagulation Be Managed Around Delivery?
- 7Switch postpartum women to LMWH or warfarin, not a DOAC, while breastfeeding → How Long After Birth, and With Which Drug?
Why This Update Matters
VTE in pregnancy complicates about 1.2 per 1,000 deliveries yet remains a leading cause of maternal death.6 In the UK it caused 16% of maternal deaths in 2021–2023, a quarter of VTE deaths occurred in the first trimester, and Black women died of VTE at more than twice the rate of white women.4 Many early deaths from VTE in pregnancy happened before any maternity contact, which is why the 2026 changes target the weeks before booking.
Who Needs Prophylaxis for VTE in Pregnancy, and When?
The risk of VTE in pregnancy doubles soon after conception, so waiting until the booking visit leaves a dangerous gap.4 NHS England’s Maternal Care Bundle now asks every service where a pregnancy is first disclosed — GP, emergency department, early pregnancy unit, abortion service — to run a brief self-assessment questionnaire.4 From booking, RCOG’s scored tool takes over and is repeated at every admission, intrapartum and after birth.2,3
Perform a VTE risk assessment at the first healthcare contact with a positive pregnancy test, not only at booking. Practice impact: a woman with a previous clot who calls her GP at six weeks should leave with a heparin prescription.
Strong RecLow EvidenceNHS MCB 2026Start LMWH within 72 hours for women with a previous confirmed VTE, hyperemesis causing dehydration or immobility, or BMI above 50 kg/m², giving an initial four-week supply.
Strong RecLow EvidenceNHS MCB 2026Do not delay early-pregnancy LMWH for a viability scan unless there is ongoing bleeding or suspected ectopic pregnancy.
Strong RecLow EvidenceNHS MCB 2026Ensure a secondary-care review within four weeks of an early prescription to reassess risk and continue treatment.
Moderate RecLow EvidenceNHS MCB 2026Repeat the formal risk score at booking, on any antenatal admission, intrapartum, immediately postpartum and on any puerperal readmission.
Strong RecLow EvidenceRCOG GTG 37a 2015RCOG PS 2026Consider LMWH from the first trimester when the antenatal score is 4 or more, and from 28 weeks when it is 3.
Moderate RecLow EvidenceRCOG PS 2026Offer LMWH throughout pregnancy and for six weeks postpartum to women with a booking BMI of 50 kg/m² or more. Practice impact: BMI 50 no longer needs a second risk factor to trigger antenatal heparin.
Strong RecLow EvidenceRCOG PS 2026Start LMWH for antenatal admissions with hyperemesis, ovarian hyperstimulation, systemic infection needing intravenous antibiotics, or immobility, and continue until the factor resolves plus one week.
Strong RecLow EvidenceRCOG PS 2026Avoid pharmacological prophylaxis in women with no or one clinical risk factor and no prior VTE or thrombophilia.
AgainstLow EvidenceASH 2018Scoring the Risk: What Tips a Woman Over the Threshold
This grid reorganises the amended RCOG factors for VTE in pregnancy by how quickly they should change the plan.
| Factor (RCOG 2026 score) | Changes the Plan When | Antenatal Action | Postnatal Action |
|---|---|---|---|
| Previous VTE, not surgery-related (4) | At first contact | LMWH from first trimester | At least 6 weeks |
| Previous surgery-provoked VTE, high-risk thrombophilia, or major comorbidity such as active lupus, IBD, nephrotic syndrome, sickle cell (3 each) | At booking | LMWH from 28 weeks, earlier if another factor | Score-driven, usually at least 10 days |
| BMI 50 kg/m² or more (4) | At booking | LMWH throughout | 6 weeks |
| BMI 40–49 kg/m² (2); age over 35, parity 3+, smoking, IVF, twins, pre-eclampsia (1 each) | When the total reaches 3 or 4 | LMWH from 28 weeks (3) or first trimester (4+) | Score 2+ means at least 10 days |
| Hyperemesis (3); OHSS, infection needing IV antibiotics, immobility, surgery (4) | On admission | LMWH while the risk lasts plus 7 days | Reassess at birth |
| Caesarean in labour (2); elective caesarean, operative birth, PPH over 1 L, preterm birth, stillbirth (1 each) | At birth | — | Score 2+ means at least 10 days |
Which LMWH Dose Should I Prescribe?
The dose question for VTE in pregnancy was settled for women with a previous clot by Highlow, which randomised 1,110 women from 70 hospitals.7 Recurrent VTE occurred in 2% with weight-adjusted intermediate dosing versus 3% with fixed low dosing (relative risk 0.69, 95% CI 0.32–1.47), with major bleeding of about 4% in both arms.7 The NHS early-pregnancy doses were built on this result.4
Prescribe fixed low-dose (prophylactic) LMWH rather than weight-adjusted intermediate dosing for antepartum and postpartum prophylaxis after a previous VTE. Practice impact: stop routinely escalating to “half-therapeutic” doses because of a past clot alone.
Strong RecHigh EvidenceHighlow 2022Prefer LMWH over unfractionated heparin for both prophylaxis and treatment in pregnancy.
Strong RecModerate EvidenceACOG PB 196ASH 2018Dose antenatal and postnatal prophylaxis by the revised RCOG weight bands from booking onwards.
Moderate RecLow EvidenceRCOG PS 2026Consider splitting the dose twice daily for enoxaparin 60–80 mg or tinzaparin 7,000–9,000 units if preferred.
Conditional RecLow EvidenceRCOG PS 2026Do not use warfarin, direct oral anticoagulants or fondaparinux as routine antenatal prophylaxis.
AgainstModerate EvidenceACOG PB 196RCOG GTG 37a 2015Heparin Doses at a Glance
Prophylactic bands for VTE in pregnancy follow the RCOG September 2026 interim table and the NHS early-pregnancy doses; therapeutic and unfractionated heparin doses follow ACOG and RCOG 37b. Confirm local formulary products, renal function and weight before prescribing, and seek specialist advice at weight extremes.
| Agent | Prophylaxis (by weight) | Therapeutic Dose | Monitoring | Main Cautions | Practical Notes |
|---|---|---|---|---|---|
| Enoxaparin | Below 100 kg: 40 mg daily; 100–129 kg: 60 mg; 130–169 kg: 80 mg; 170 kg+: 0.6 mg/kg/day | 1 mg/kg twice daily or 1.5 mg/kg once daily, by early-pregnancy weight | Anti-Xa only at weight extremes, renal impairment or recurrence | Bleeding, bruising, rare skin reactions | Pre-booking NHS dose: 40 mg (below 100 kg), 60 mg (above 100 kg) |
| Dalteparin | Below 100 kg: 5,000 units; 100–129 kg: 7,500; 130–169 kg: 10,000; 170 kg+: 75 units/kg/day | 100 units/kg twice daily or 200 units/kg once daily | As for enoxaparin | As for enoxaparin | Same bands pre-booking below and above 100 kg |
| Tinzaparin | Below 100 kg: 4,500 units; 100–129 kg: 7,000; 130–169 kg: 9,000; 170 kg+: 75 units/kg/day | 175 units/kg once daily | As for enoxaparin | As for enoxaparin | NHS pre-booking dose below 100 kg is 3,500 units — check which table applies |
| Unfractionated heparin | 5,000–7,500 units 12-hourly (1st trimester), 7,500–10,000 (2nd), 10,000 (3rd) | 10,000 units or more 12-hourly, adjusted to aPTT 1.5–2.5 times control | aPTT; platelet count for HIT | Heparin-induced thrombocytopenia; osteoporosis with long use | Reversible and short-acting; useful near delivery or with renal failure |
| Warfarin | Not used antenatally | Postpartum only, target INR 2–3 | INR | Embryopathy in early pregnancy; fetal bleeding | Compatible with breastfeeding |
| DOACs (apixaban, rivaroxaban, dabigatran) | Not recommended | Not recommended | — | Uncertain fetal and infant safety | Avoid in pregnancy and while breastfeeding |
Who Needs Prophylaxis After a Previous Clot?
A previous clot is the strongest single risk factor for VTE in pregnancy, but ACOG and RCOG draw the treatment line in different places. RCOG treats almost every prior VTE as high risk from the first trimester; ACOG and ASH allow antepartum surveillance when the earlier event had a clear non-hormonal trigger.1,3,6 Both agree that postpartum prophylaxis is needed after any previous VTE.
Offer prepregnancy counselling and a written thromboprophylaxis plan to every woman with a previous VTE.
Strong RecLow EvidenceRCOG GTG 37a 2015Start antepartum LMWH prophylaxis for a previous unprovoked or oestrogen- or pregnancy-related VTE.
Strong RecLow EvidenceASH 2018ACOG PB 196Consider antepartum surveillance rather than LMWH after a single VTE provoked by a transient non-hormonal factor such as surgery, when no thrombophilia or other risk factor is present.
Conditional RecLow EvidenceACOG PB 196ASH 2018Prescribe postpartum prophylaxis for six weeks for every woman with a previous VTE.
Strong RecLow EvidenceACOG PB 196RCOG GTG 37a 2015Switch women on long-term anticoagulation to LMWH at therapeutic or near-therapeutic dose under specialist direction.
Strong RecLow EvidenceACOG PB 196RCOG GTG 37a 2015Advise women on warfarin or a DOAC who are trying to conceive to test for pregnancy often and switch to LMWH as soon as a test is positive, ideally before six weeks. Practice impact: give the instruction and a heparin prescription in advance, so the switch does not wait for an appointment.
Moderate RecLow EvidenceRCOG GTG 37a 2015ASH 2018Evaluate for thrombophilia when a previous non-oestrogen VTE had only a minor provoking factor, because the result changes antenatal management.
Conditional RecLow EvidenceRCOG GTG 37a 2015Consider postpartum prophylaxis for asymptomatic high-risk thrombophilia, and add antepartum LMWH when there is a first-degree family history of VTE.
Moderate RecLow EvidenceACOG PB 196Prior-Clot Scenarios Side by Side
| Scenario | Antepartum (ACOG) | Antepartum (RCOG) | Postpartum (both) |
|---|---|---|---|
| Single VTE provoked by major surgery, no thrombophilia | Surveillance | LMWH from 28 weeks (score 3), earlier with other factors | Prophylactic LMWH for 6 weeks |
| Single unprovoked or hormone-related VTE | Prophylactic LMWH | Prophylactic LMWH from first trimester | 6 weeks |
| Prior VTE with high-risk thrombophilia | Prophylactic, intermediate or adjusted dose, individualised | Specialist-led LMWH from first trimester | 6 weeks, same or higher dose |
| Two or more VTEs, or long-term anticoagulation | Adjusted (therapeutic) dose | Therapeutic or near-therapeutic, specialist-led | Resume long-term plan |
| Low-risk thrombophilia, no VTE, first-degree family history | Surveillance or prophylactic | Score 1 plus other factors | 6 weeks (RCOG); prophylactic or intermediate (ACOG) |
How Should Suspected VTE in Pregnancy Be Confirmed?
Leg swelling and breathlessness are common in normal pregnancy, so objective testing is essential. ACOG and RCOG 37b both advise against using D-dimer alone to exclude VTE in pregnancy, because levels climb with each trimester.1,5 Two prospective management studies have since shown that pregnancy-adapted algorithms combining clinical rules, D-dimer and leg ultrasound can safely rule out pulmonary embolism.8,9
Start therapeutic LMWH as soon as VTE is clinically suspected, unless contraindicated, and continue until the diagnosis is excluded.
Strong RecLow EvidenceRCOG GTG 37b 2015Perform compression duplex ultrasound for suspected deep vein thrombosis.
Strong RecModerate EvidenceACOG PB 196RCOG GTG 37b 2015Repeat ultrasound at day 3 and day 7, or consider magnetic resonance venography, when the first scan is negative but suspicion stays high, especially for suspected iliac vein thrombosis.
Moderate RecLow EvidenceRCOG GTG 37b 2015ACOG PB 196Perform leg ultrasound first in suspected pulmonary embolism with leg symptoms; a positive scan confirms VTE and avoids chest imaging.
Strong RecModerate EvidenceRCOG GTG 37b 2015Artemis 2019Obtain a chest X-ray, then choose ventilation-perfusion scanning or CT pulmonary angiography according to the film and local availability.
Strong RecModerate EvidenceACOG PB 196RCOG GTG 37b 2015Consider a validated pregnancy-adapted pathway (pregnancy-adapted YEARS, or revised Geneva with high-sensitivity D-dimer) to reduce chest imaging where local protocols support it. Practice impact: a low-probability woman in the first trimester may safely avoid CT altogether.
Conditional RecModerate EvidenceArtemis 2019CT-PE-Pregnancy 2018ESC 2019Do not withhold indicated imaging because of fetal radiation concerns; the fetal dose from either chest modality is well below harmful thresholds.
AgainstModerate EvidenceACOG PB 196Clinical Decision Pathway
A question-based route through VTE in pregnancy, from first contact to the postnatal plan.
How Should Acute VTE in Pregnancy Be Treated?
Treatment of acute VTE in pregnancy is weight-based LMWH for the rest of the pregnancy. RCOG and ASH accept once- or twice-daily dosing, based on early-pregnancy weight.5,6 Routine anti-Xa and platelet monitoring is not needed for most women on LMWH alone.5
Start weight-based therapeutic LMWH for confirmed DVT or pulmonary embolism, calculated on booking or early-pregnancy weight.
Strong RecModerate EvidenceRCOG GTG 37b 2015ASH 2018Continue therapeutic anticoagulation for the rest of pregnancy and at least six weeks postpartum, with a total of at least three months.
Strong RecLow EvidenceRCOG GTG 37b 2015ACOG PB 196Avoid routine anti-Xa monitoring; consider it at weight extremes (below 50 kg or 90 kg and above), in renal impairment or after recurrent VTE.
Conditional RecLow EvidenceRCOG GTG 37b 2015Use intravenous unfractionated heparin as initial treatment for massive pulmonary embolism with cardiovascular compromise.
Moderate RecLow EvidenceRCOG GTG 37b 2015Consider systemic thrombolysis for pulmonary embolism with life-threatening haemodynamic instability, involving a multidisciplinary team.
Conditional RecLow EvidenceASH 2018RCOG GTG 37b 2015Consider LMWH for symptomatic superficial vein thrombosis in pregnancy.
Conditional RecLow EvidenceASH 2018Consider a temporary inferior vena cava filter only when anticoagulation is contraindicated or proximal VTE occurs very close to delivery.
Conditional RecLow EvidenceRCOG GTG 37b 2015ACOG PB 196How Should Anticoagulation Be Managed Around Delivery?
The peripartum plan for VTE in pregnancy balances clot, bleeding and access to epidural or spinal anaesthesia. ACOG allows switching to unfractionated heparin from 36 weeks, while RCOG and ASH favour planned delivery with LMWH stopped in advance.1,5,6 SOAP consensus sets the minimum intervals before neuraxial procedures.11
Document a delivery, anaesthetic and postpartum anticoagulation plan by 36 weeks, agreed with anaesthesia and haematology.
Strong RecLow EvidenceRCOG GTG 37b 2015ACOG PB 196Plan delivery for women on therapeutic LMWH and give the last dose at least 24 hours before induction or caesarean.
Moderate RecLow EvidenceASH 2018RCOG GTG 37b 2015Advise women on LMWH not to inject once labour starts or bleeding begins, and to attend for assessment.
Strong RecLow EvidenceRCOG GTG 37a 2015Consider switching to unfractionated heparin at about 36 weeks, or earlier if preterm birth is likely, when neuraxial access is a priority.
Conditional RecLow EvidenceACOG PB 196Wait at least 12 hours after prophylactic LMWH and 24 hours after therapeutic LMWH before a neuraxial procedure.
Strong RecLow EvidenceSOAP 2018ACOG PB 196Wait at least 4–6 hours after subcutaneous unfractionated heparin 5,000 units before a neuraxial procedure.
Moderate RecLow EvidenceSOAP 2018Give the first postpartum LMWH dose at least 4 hours after epidural catheter removal, and do not remove the catheter within 12 hours of the last injection.
Strong RecLow EvidenceRCOG GTG 37a 2015SOAP 2018Restart anticoagulation no sooner than 4–6 hours after vaginal birth or 6–12 hours after caesarean, once bleeding is controlled.
Moderate RecLow EvidenceACOG PB 196How Long After Birth, and With Which Drug?
The weeks after birth carry the highest daily risk of VTE in pregnancy and the puerperium, and caesarean birth is where US and UK practice differ most. ACOG recommends pneumatic compression for every caesarean in women not already on anticoagulation, reserving heparin for added risk; RCOG’s scoring gives most emergency caesareans at least 10 days of LMWH.1,3
Apply pneumatic compression devices before caesarean in all women not already receiving thromboprophylaxis.
Strong RecLow EvidenceACOG PB 196Prescribe LMWH for at least 10 days when the postnatal score is 2 or more, including after caesarean in labour.
Moderate RecLow EvidenceRCOG PS 2026Prescribe six weeks of postnatal LMWH after previous VTE, with high-risk thrombophilia, with a BMI of 50 kg/m² or more, or with low-risk thrombophilia plus a first-degree family history.
Strong RecLow EvidenceRCOG PS 2026ACOG PB 196Consider extending prophylaxis to six weeks when three or more risk factors persist after birth.
Conditional RecLow EvidenceRCOG GTG 37a 2015Give LMWH for one week after miscarriage or abortion in women identified as high risk, restarting 6 hours after surgical procedures.
Moderate RecLow EvidenceNHS MCB 2026Offer LMWH or warfarin for postnatal treatment of VTE; both are compatible with breastfeeding.
Strong RecModerate EvidenceRCOG GTG 37b 2015ACOG PB 196Avoid starting warfarin until at least the fifth postnatal day, and later when postpartum haemorrhage risk is high, overlapping with LMWH until the INR is 2 or above on two consecutive days.
Moderate RecLow EvidenceRCOG GTG 37b 2015Do not use direct oral anticoagulants in women who are breastfeeding.
AgainstLow EvidenceRCOG GTG 37a 2015ACOG PB 196Counsel against oestrogen-containing contraception after a pregnancy-associated VTE.
AgainstLow EvidenceRCOG GTG 37b 2015Who Needs a Different Approach?
Several groups need the standard framework for VTE in pregnancy adjusted rather than replaced. Mechanical heart valves need a separate specialist strategy and are outside this update.
Refer women with antithrombin deficiency, antiphospholipid syndrome with prior thrombosis, or multiple thrombophilias to a thrombosis-in-pregnancy specialist early.
Strong RecLow EvidenceRCOG GTG 37a 2015Consider persistent antiphospholipid antibodies without prior VTE as a risk factor that adds to others in the score.
Conditional RecLow EvidenceRCOG GTG 37a 2015Evaluate women with cancer, heart failure, active lupus, inflammatory bowel disease or polyarthropathy, nephrotic syndrome, sickle cell disease or current intravenous drug use as scoring 3 points, and involve the relevant specialist in the plan.
Moderate RecLow EvidenceRCOG PS 2026Evaluate bleeding risk with haematology before prophylaxis in placenta praevia, known bleeding disorders, thrombocytopenia or active antenatal bleeding.
Strong RecLow EvidenceRCOG GTG 37a 2015RCOG PS 2026Ensure equitable access to risk assessment and heparin supply, including interpreters and free prescriptions, given the higher VTE death rate among Black women.
Moderate RecLow EvidenceNHS MCB 2026Monitoring VTE in Pregnancy Treatment and Follow-Up
Monitoring keeps VTE in pregnancy prophylaxis on track: a dose that fitted at eight weeks may not fit at 30, and plans drift when women move between services.2
Reassess VTE risk and LMWH dose at every antenatal admission, at 28 weeks and at delivery.
Strong RecLow EvidenceRCOG GTG 37a 2015Monitor platelet count in women receiving unfractionated heparin, or after previous unfractionated heparin exposure.
Moderate RecLow EvidenceRCOG GTG 37b 2015ACOG PB 196Reassess at the end of treatment and plan prophylaxis for any future pregnancy after a pregnancy-associated VTE.
Moderate RecLow EvidenceRCOG GTG 37b 2015| What to Check | When | Why It Matters | Common Pitfall |
|---|---|---|---|
| Risk score | First contact, booking, each admission, intrapartum, postpartum | Risk changes quickly with admissions and mode of birth | Scoring once at booking only |
| Weight band | Booking; recheck with major weight change | Doses are weight-banded | Keeping an early dose after crossing 100 kg |
| Platelet count | Only with unfractionated heparin exposure | Detects heparin-induced thrombocytopenia | Routine counts on LMWH alone add little |
| Anti-Xa level | Weight extremes, renal impairment, recurrence | Guides therapeutic dosing | Measuring routinely or at the wrong time |
| Last-dose time | Onset of labour; before neuraxial | Sets the safe interval | Not recording when the last injection was given |
| INR | Postpartum warfarin start | Stop LMWH when INR is 2+ twice | Starting warfarin too early after birth |
Evidence in Context
How ACOG, RCOG and the trials on VTE in pregnancy line up.
Where ACOG and RCOG Agree▾
Both prefer LMWH, avoid warfarin and DOACs in pregnancy, give six weeks of postpartum prophylaxis after previous VTE, treat acute VTE for the rest of pregnancy and at least six weeks postpartum, and respect neuraxial intervals.
Where They Differ▾
RCOG uses a cumulative score that places many more women on antenatal and postnatal LMWH, especially after caesarean and with obesity. ACOG uses scenario-based tables, recommends mechanical prophylaxis for all caesareans, and permits antepartum surveillance after a surgically provoked VTE.
What Comes Next▾
The full RCOG update of Green-top Guideline 37a is expected in spring 2027; until then the September 2026 amendments apply.
What the Trials Add▾
Highlow is the only large randomised trial of prophylactic dose and supports low-dose LMWH. Artemis and CT-PE-Pregnancy validated D-dimer-based pathways for suspected pulmonary embolism, which the ESC accepts.
Evidence Gaps
These are the open questions in VTE in pregnancy that clinicians meet in practice, where current advice rests largely on observational data or consensus.
- Whether routine LMWH after caesarean prevents clinically important VTE has not been shown in an adequately powered trial.
- The RCOG scoring thresholds for VTE in pregnancy, and their revised weights, have not been prospectively validated for antenatal decisions.
- Whether intermediate dosing benefits the postpartum period specifically, as a Highlow post-hoc signal suggests, is untested.
- The effect of pre-booking LMWH on first-trimester VTE deaths will only be known from future confidential enquiries.
- Once-daily versus twice-daily therapeutic LMWH, and the value of anti-Xa targets, lack comparative data in pregnancy.
- Safety data for DOACs in breastfeeding remain too limited to support use.
References
- 1.American College of Obstetricians and Gynecologists’ Committee on Practice Bulletins—Obstetrics. ACOG Practice Bulletin No. 196: Thromboembolism in pregnancy. Obstet Gynecol. 2018;132(1):e1-e17 (reaffirmed 2025). https://doi.org/10.1097/AOG.0000000000002706
- 2.Royal College of Obstetricians and Gynaecologists. Reducing the risk of venous thromboembolism during pregnancy and the puerperium. Green-top Guideline No. 37a. London: RCOG; 2015. https://www.rcog.org.uk/guidance/browse-all-guidance/green-top-guidelines/reducing-the-risk-of-thrombosis-and-embolism-during-pregnancy-and-the-puerperium-green-top-guideline-no-37a/
- 3.Royal College of Obstetricians and Gynaecologists. Green-top Guideline No. 37a — Position statement (interim amendments aligned with the NHS England Maternal Care Bundle). London: RCOG; September 2026. https://www.rcog.org.uk/media/bzkdicre/position-statement-gtg37a-final-version.pdf
- 4.NHS England. The Maternal Care Bundle: a care bundle for reducing maternal mortality and morbidity. Element 1: Venous thromboembolism. Publication reference PRN02177. 2026. https://www.england.nhs.uk/long-read/the-maternal-care-bundle/
- 5.Royal College of Obstetricians and Gynaecologists. Thrombosis and embolism during pregnancy and the puerperium: acute management. Green-top Guideline No. 37b. London: RCOG; 2015. https://www.rcog.org.uk/guidance/browse-all-guidance/green-top-guidelines/thrombosis-and-embolism-during-pregnancy-and-the-puerperium-acute-management-green-top-guideline-no-37b/
- 6.Bates SM, Rajasekhar A, Middeldorp S, et al. American Society of Hematology 2018 guidelines for management of venous thromboembolism: venous thromboembolism in the context of pregnancy. Blood Adv. 2018;2(22):3317-3359. https://doi.org/10.1182/bloodadvances.2018024802
- 7.Bistervels IM, Buchmüller A, Wiegers HMG, et al. Intermediate-dose versus low-dose low-molecular-weight heparin in pregnant and post-partum women with a history of venous thromboembolism (Highlow study): an open-label, multicentre, randomised, controlled trial. Lancet. 2022;400(10365):1777-1787. https://doi.org/10.1016/S0140-6736(22)02128-6
- 8.van der Pol LM, Tromeur C, Bistervels IM, et al. Pregnancy-adapted YEARS algorithm for diagnosis of suspected pulmonary embolism. N Engl J Med. 2019;380(12):1139-1149. https://doi.org/10.1056/NEJMoa1813865
- 9.Righini M, Robert-Ebadi H, Elias A, et al. Diagnosis of pulmonary embolism during pregnancy: a multicenter prospective management outcome study. Ann Intern Med. 2018;169(11):766-773. https://doi.org/10.7326/M18-1670
- 10.Konstantinides SV, Meyer G, Becattini C, et al. 2019 ESC guidelines for the diagnosis and management of acute pulmonary embolism developed in collaboration with the European Respiratory Society. Eur Heart J. 2020;41(4):543-603. https://doi.org/10.1093/eurheartj/ehz405
- 11.Leffert L, Butwick A, Carvalho B, et al. The Society for Obstetric Anesthesia and Perinatology consensus statement on the anesthetic management of pregnant and postpartum women receiving thromboprophylaxis or higher dose anticoagulants. Anesth Analg. 2018;126(3):928-944. https://doi.org/10.1213/ANE.0000000000002530
How to Read the Evidence Tags
Every recommendation carries a strength tag and an evidence tag — Medaptly’s own simplified reading of the underlying guidance, not a reproduction of any source body’s grading system.
| Strength Tag | What It Means |
|---|---|
| Strong Rec | High-quality evidence broadly supports this action |
| Moderate Rec | The weight of evidence favours this action |
| Conditional Rec | The benefit is less certain — individualise |
| Against | Evidence points to no benefit or potential harm |
| Evidence Tag | What It Means |
|---|---|
| High Evidence | Multiple well-designed trials or high-quality meta-analyses |
| Moderate Evidence | A single trial or large observational dataset |
| Low Evidence | Expert consensus or small studies |