An evidence-based clinical review for the assessment of deep vein thrombosis and pulmonary embolism risk during pregnancy and puerperium, thromboprophylaxis selection based on risk scoring, low molecular weight heparin (LMWH) dosing principles, and peripartum management.
⚕️ Target audience: This clinical review is intended for physicians and healthcare professionals; It is a summary of current literature and guidelines for educational purposes. Clinical decisions should be made based on patient-specific evaluation and applicable institutional protocols.
Venous thromboembolism (VTE), which includes deep vein thrombosis (DVT) and pulmonary embolism (PE), is a well-defined complication of pregnancy and the postpartum period. The risk of VTE in pregnant and postpartum women is approximately four to five times increased compared to their non-pregnant counterparts; Approximately 80% of events are of venous origin, with a prevalence of 0.5–2.0 per 1,000 pregnancies (ACOG Practice Bulletin No. 196, 2018). According to American Society of Hematology (ASH) data, VTE complicates approximately 1.2 of every 1,000 births; Although the absolute risk is low, pregnancy-related VTE is one of the main preventable causes of maternal mortality and morbidity in developed countries (ASH 2018).
The temporal distribution of risk is clinically critical: the daily risk of VTE is highest during the puerperal period, especially in the first 3–6 weeks postpartum; Therefore, the postpartum period is also weighed in prophylaxis decisions (RCOG Green-top Guideline No. 37a, 2015). For anatomical reasons (the gravid uterus compresses the left iliac vein at the point where it crosses the right iliac artery), the majority of DVTs during pregnancy are located in the left leg and iliofemoral region; this is a different distribution than the non-pregnant population (UpToDate, “Venous thromboembolism in pregnancy and postpartum: Prevention”).
Pregnancy is an acquired prothrombotic state that physiologically activates all three components of the Virchow triad:
The risk increases even more when hereditary or acquired thrombophilia is added to this physiological basis. Thrombophilia occurs in approximately 10% of the white population but is partially responsible for approximately half of VTE events in pregnancy (UpToDate, “Inherited thrombophilias in pregnancy”). Factor V Leiden and prothrombin G20210A variants account for 50–60% of inherited thrombophilia in the white population.
All pregnant women should be evaluated for the risk of VTE and bleeding before pregnancy or in the early stages of pregnancy, if possible; It should be reconsidered in the development of complications such as preeclampsia, changes in status such as transition from pregnancy to puerperium or from outpatient to inpatient monitoring (UpToDate; RCOG GTG 37a 2015). Major risk factors evaluated include previous history of VTE and nature of the triggering event (provoked/unprovoked, estrogen-related), family history, known hereditary thrombophilia, antiphospholipid syndrome, comorbid medical conditions (systemic lupus, inflammatory bowel disease, sickle cell anemia, heart disease), obesity, smoking, varicose veins, and prolonged immobilization.
The national resource for Türkiye is the VTE section in the Ministry of Health Risky Pregnancies Management Guide 2026 (Publication Number 1414). Read together Table 1 scores, Table 2 general thresholds, and Table 3 specific management of previous VTE/thrombophilia. (Ministry of Health, 2026) The RCOG model includes the September 2026 Position Statement changes along with the 2023 corrected copy of the 2015 guide; This interim update is used just as the new guide is being prepared. ( RCOG, September 2026 ) ( RCOG, 2015/2023 ) Scores and times of the two models are not combined.
ACOG and UpToDate use a history-based categorical approach; UpToDate notes that it does not typically use specific pregnancy VTE score tools. Therefore, the Ministry of Health/RCOG total score is not a VTE percentage or UpToDate-verified risk estimate. In the VTE assessment tool on the site, the Ministry and the RCOG are selected separately. (in the VTE assessment tool)
| Period / condition | Ministry of Health 2026 | RCOG 37a + September 2026 |
|---|---|---|
| Antenatal ≥4 points | Thromboprophylaxis is recommended starting from the first trimester. | LMWH is considered starting from the first trimester; In temporary risk, the duration of the risk is also a determining factor. |
| Antenatal 3 points | Recommended from the 28th week. | Consider from the 28th week; do not wait in the presence of independent indications such as hospitalization/HG. |
| Postpartum 2–3 points | At least 10 days. | At least 10 days; higher risk/antenatal need or longer plan in special group. |
| Postpartum ≥4 points | At least 6 weeks. | The general Annex I threshold is at least 10 days; High risk, antenatal LMWH requirement, permanent risk and special rules prolong the duration. The Ministry's ≥4→6 week rule is not automatically transferred. |
| Baseline BMI ≥50 | BMI line is 2 points; There is no separate 4 point rule. | LMWH is recommended throughout pregnancy and for 6 weeks postpartum. |
| Admission | Antenatal hospitalization; Hospitalization or readmission in the puerperium for ≥3 days requires prophylaxis separate from the score. | Antenatal hospitalization and puerperal repeat/extended hospitalization are evaluated separately from the score. |
Sources: Ministry Table 2 and postpartum section; RCOG 2015 Part 4.1/7.5, Annex I and September 2026 Annex I. ( Ministry of Health, 2026 ) ( RCOG, September 2026 ) ( RCOG, 2015/2023 ) A low score does not exclude VTE. Postpartum risk is reassessed; Just because LMWH has been used for a short time for a temporary antenatal risk does not automatically mean 6 weeks without other information.
| Risk factor | Ministry 2026 | RCOG + September 2026 | Scope / exception |
|---|---|---|---|
| Previous VTE other than a single major surgery-related event | 4 | 4 | Expert management; At least 6 weeks postpartum in previous VTE. |
| Previous VTE triggered by a single, major surgery | 3 | 3 | Single event and absence of additional risk are evaluated separately; The overall score alone does not give a plan. |
| Antithrombin, proteinC/S deficiency; homozygous or multiple thrombophilias | 3 | 3 | Antithrombin, protein C/S deficiency, homozygous/combined defect; expert way. |
| Identified significant comorbid disease | 3 | 3 | Cancer, heart failure, active SLE/IBD/polyarthropathy, nephrotic syndrome, Type 1 DM with nephropathy, sickle cell disease, current IV drug dependence. The group is counted once. |
| Unprovoked or estrogen-related VTE in a first-degree relative | 1 | 1 | Not expanded to a history of any clot in any relative. |
| Heterozygous FVL or heterozygous prothrombin G20210A in the absence of a VTE history | 1 | 1 | Heterozygous FVL or prothrombin G20210A; protein C/S does not enter this line. |
| Age>35 | 1 | 1 | 35 years: 0; 36 years and older: 1. |
| Pregnancy onset BMI | 30–39,9: 1; ≥40: 2 | 30–39,9: 1; 40–49,9: 2; ≥50: 4 | BMI at the start of pregnancy; do not add the bands together. For BMI ≥50, RCOG also recommends prophylaxis throughout pregnancy + 6 weeks postpartum. |
| Parity≥3 | 1 | 1 | Once the third delivery has occurred, parity (para) becomes 3. |
| Cigarette | 1 | 1 | Ministry: >10 units/day; RCOG: active smoking. |
| Large/prominent varicose vein | 1 | 1 | Definitions are given separately in the description below. |
| Preeclampsia in this pregnancy | 1 | 1 | In the context of the current pregnancy/birth. |
| ART/IVF | 1 | 1 | Antenatal only; It is not carried over to the postpartum score. |
| Multiple pregnancy | 1 | 1 | Current pregnancy. |
| Caesarean section in labor | 2 | 2 | Count only an actual cesarean delivery during labor; do not also count elective CS. |
| Elective caesarean section | 1 | 1 | If there is additional risk, the total and specific CS recommendation is evaluated separately. |
| Mid/rotational invasive birth | 1 | 1 | Ministry: medium/rotational forceps. It is not generalized to every operative vaginal birth. |
| Labor >24 hours | 1 | 1 | A full 24 hours is not enough; >24 hours. |
| Bleeding >1 liter or transfusion | 1 | 1 | Bleeding and transfusion as one score on the same line; active bleeding is a safety barrier. |
| Birth in this pregnancy<37+0 weeks | 1 | 1 | Actual birth <37+0; Being less than 37 weeks pregnant does not give this score. |
| Stillbirth in this pregnancy | 1 | 1 | The result of birth during this pregnancy. |
| Other surgery during pregnancy/puerperium | 3 | 4 | E.g. appendectomy, postpartum sterilization. The same CS a second time does not count as additional surgery. |
| Hyperemesis gravidarum | 3 | 3 | Antenatal. RCOG: offering LMWH within 72 hours in defined severe HG; hospitalization/immobility period also. |
| Ovarian hyperstimulation syndrome | 4 | 4 | First trimester; The temporary risk period marked RCOG applies. |
| Current systemic infection | 1 | 4 | RCOG: Systemic infection requiring IV antibiotics or hospitalization. |
| Immobilization or dehydration | 1 | 4 | Immobilization ≥3 days / dehydration; the same row is not counted twice. |
| Long trip>4hours | 1 | No separate rows in new scoreboard | Points in the Ministry; Within the scope of RCOG 2015 general risk, there is no separate line in the September 2026 renewed Annex I score. |
Definition of varicose veins: The Ministry footnote defines varicose veins that are prominent above the kneecap, exceed 1 cm in diameter, and cause skin discoloration, including pelvic varicose veins. RCOG defines prominent varicose veins that are symptomatic, above the knee, or associated with phlebitis, edema, or skin changes. (Ministry of Health, 2026) (RCOG, 2015/2023)
Temporary risk period: The Ministry table evaluates temporary risks until the risk disappears. In RCOG September 2026, other surgery, OHSS, qualified systemic infection and immobilization/dehydration lines are 4 points; LMWH is planned for another 7 days as long as the risk persists and after it improves. Correction of risk does not eliminate the continuation window. In defined severe hyperemesis, LMWH is indicated to be offered within 72 hours; For those hospitalized with HG or other temporary immobility-related condition, continue until risk resolves and then for another week. (RCOG, September 2026)
Mode of delivery: Cesarean delivery in labor scores 2 points; elective cesarean delivery scores 1 point. Urgent/unplanned cesarean delivery before labor begins is not explicitly scored within the Ministry table's binary split; scores must not be improvised. RCOG Section 7.4 recommends considering 10 days of LMWH after non-elective cesarean delivery, and 10 days after elective cesarean delivery if an additional risk factor is present. (Ministry of Health, 2026) (RCOG, 2015/2023)
The highest risk pregnant women requiring prophylaxis are (UpToDate): a single unprovoked episode of VTE; a single estrogen-related VTE (pregnancy, oral contraceptive, ovarian hyperstimulation); recurrent VTE (regardless of provoked/unprovoked distinction); and a single episode of VTE accompanied by a persistent risk factor (immobilization, active cancer). The risk of recurrence in pregnant women with a previous history of VTE is between 2.5–11%; At the upper end of this range are unprovoked, recurrent, and hormone/pregnancy-related VTEs. In women who are provoked only by a major temporary cause (surgery, trauma) and do not have additional risk factors, prophylaxis is usually reserved only for the postpartum period.
Not every pregnant woman with hereditary thrombophilia requires prophylaxis; The decision is made based on the type of thrombophilia and personal/family history of VTE, often in collaboration with hematology. The absolute VTE risks of high-risk and low-risk thrombophilias during pregnancy + puerperium are summarized below (UpToDate, "Inherited thrombophilias in pregnancy").
| Thrombophilia | Risk class | Pregnancy + puerperium VTE risk |
|---|---|---|
| Antithrombin deficiency | High | ~6.1% (<35 years) – 9.0% (≥35 years) |
| Factor V Leiden + prothrombin G20210A (combined heterozygous) | High | ~5.5% – 8.2% |
| Factor V Leiden homozygous | High | ~2.2% – 3.4% |
| Factor V Leiden heterozygous | Low | ~0.5% – 0.7% |
| Prothrombin G20210A heterozygous | Low | ~0.4% – 0.6% |
| Protein C or protein S deficiency | Low | ~0.7% – 1.1% |
Risk class depends on source context: The protein C/S designation in the absolute-risk table above is not the same label as the Department/RCOG score group. The Ministry considers Table 1 and RCOG protein C/S deficiency as high-risk thrombophilia, 3 points. The RCOG recommends specialist evaluation and 6 weeks of postnatal prophylaxis in this asymptomatic high-risk group, even if there is no additional risk. The Ministry's Table 3 gives 7 days for asymptomatic thrombophilias other than antithrombin/combined/homozygous or 6 weeks for family/additional risk; There is a time/approach mismatch between the general Table 2 and these specific rows. The tool does not automatically reduce this difference to 7 or 10 days; An expert plan is required. MTHFR and PAI-1 variants do not bring VTE prophylaxis points in the Ministry; RCOG also states to ignore MTHFR. (Ministry of Health, 2026) (RCOG, 2015/2023)
Previous VTE exception: Single major surgery-related event distinguished from other types of VTE. While the Ministry's Table 2 gives the 28th week approach with a total of 3 points, Table 3 advises considering antenatal prophylaxis, rather than routinely recommending it, for a single VTE due to a transient cause without additional risk factors. In RCOG, there is expert evaluation for this group instead of routine prophylaxis in early pregnancy, and in Annex IV there is an approach starting from the 28th week. Confirmed previous VTE requires at least 6 weeks postpartum, regardless of mode of delivery. Antithrombin deficiency, APS+VTE and long-term anticoagulation are expert groups independent of the simple score. (Ministry of Health, 2026) (RCOG, 2015/2023)
Antiphospholipid syndrome (acquired thrombophilia) significantly increases the risk of both venous and arterial thrombosis; The risk is proportional to the number of positive antibodies (at the highest triple positivity) and titer size, and its management is discussed under a separate heading.
The main agent of thromboprophylaxis in pregnancy is low molecular weight heparin (LMWH). Heparins do not cross the placenta and do not cause fetal anticoagulation; LMWH provides a more predictable anticoagulant response compared to unfractionated heparin (UFH), does not require routine monitoring, and has a lower risk of heparin-associated thrombocytopenia (HIT) (UpToDate, "Anticoagulation during pregnancy and postpartum: Agent selection and dosing"). A systematic review covering 64 studies and 2,777 pregnancies found LMWH to be safe and effective (venous thrombosis 0.8%, significant bleeding 2%, no cases of HIT reported).
UpToDate defines three levels for dosing: low dose (prophylaxis), intermediate dose (prophylaxis adjusted for gestational weight gain), and therapeutic dose (VTE treatment). Ministry 2026 and RCOG's tables with different dates use different bands according to weight. The following lines are separated by the resource name; high risk, renal function, bleeding, and delivery/anesthesia schedule may alter dosing decisions.
| Level | Dose | Source / note |
|---|---|---|
| Low dose prophylaxis (fixed) | Enoxaparin 40 mg/day (body weight <100 kg); 60 mg/day (≥100 kg). Dalteparin 5,000 units/day. | UpToDate; Highlow trial |
| Low dose prophylaxis (banded by weight) | <50 kg: 20 mg/day · 50–90 kg: 40 mg/day · 91–130 kg: 60 mg/day · 131–170 kg: 80 mg/day · >170 kg: 0.6 mg/kg/day | Ministry of Health 2026 Table 4; RCOG 2015 historical Table 3. Higher bands with asterisks can be given in two divided doses. (Ministry of Health, 2026) (RCOG, 2015/2023) |
| RCOG September 2026 — updated prophylaxis bands | <100 kg: 40 mg/day · 100–129 kg: 60 mg/day · 130–169 kg: 80 mg/day · ≥170 kg: 0.6 mg/kg/day . The last three weight bands can be given in two divided doses. | RCOG Position Statement Table 1; replaces the previous RCOG dosing table and refers to the NHS MCB recommendations for the period before initial antenatal booking. (RCOG, September 2026) |
| Medium dose | Enoxaparin should be increased according to weight gain at a maximum dose of 1 mg/kg once a day. | UpToDate |
| Therapeutic dose | Enoxaparin 1 mg/kg every 12 hours (2×/day) or dalteparin 100 units/kg every 12 hours | UpToDate (2× daily is preferred over single dose) |
| UFH prophylaxis (by trimester) | 5,000–7,500 U (T1) → 7,500–10,000 U (T2) → 10,000 U (T3), every 12 hours | UpToDate |
The open-label randomized Highlow study (Lancet 2022; PMID 36354038), which included 1,110 women with a previous history of VTE and an indication for antepartum prophylaxis, compared a weight-adjusted intermediate dose with a fixed low dose. The risk of VTE was similar in the two groups (intermediate-dose 2% versus low-dose 3%; relative risk 0.69; 95% CI 0.32–1.47), and rates of clinically significant bleeding were also similar (4% in both groups). ASH 2018 Recommendation 28 recommends, with a conditional, very low certainty of evidence, that the intermediate dose should not be used instead of the antepartum standard dose in pregnant women requiring prophylaxis; this recommendation predates the 2022 Highlow study ( ASH, 2018 ). Individual evaluation remains important in weight extremes and very high-risk cases.
In the highest risk patients, prophylaxis is initiated when pregnancy is diagnosed and continued throughout pregnancy and for at least 6 weeks postpartum (as long as the risk of bleeding is considered low). In the highest risk group (e.g. unprovoked VTE + persistent risk factor) the period can be extended up to 3 months after birth. In other risk groups, timing and duration are individualized; The postpartum threshold is generally lower than antepartum because the risk of VTE is highest and the potential for obstetric bleeding is lowest (UpToDate). In cases requiring antepartum hospitalization (nondelivery) (critical illness, nonobstetric surgery, orthopedic injury, hospitalization for >3 days, hyperemesis, preeclampsia), prophylaxis is applied with the same criteria as for non-pregnant patients.
Mechanical methods are preferred instead of pharmacological prophylaxis in pregnant women with a high risk of bleeding (e.g. uncontrolled hypertension, placenta previa, abruption, expanding subchorionic hematoma, bleeding diathesis); The primary option is intermittent pneumatic compression devices, graduated compression stockings are the alternative (UpToDate, Grade 2C). Graduated compression stockings are not used alone for primary VTE prevention; Its main use is symptom relief in post-thrombotic syndrome and in the presence of contraindications to pharmacological prophylaxis. Pharmacological prophylaxis is initiated or restarted once the risk of bleeding has decreased to an acceptable level; some experts prefer UFH in this situation due to its short half-life and reversibility with protamine sulfate.
Anticoagulation during labor should be discontinued except in the highest risk situations; Normal coagulation is necessary for both safe neuraxial anesthesia and the prevention of excessive bleeding at birth. Neuraxial techniques (spinal, epidural, combined) are not performed in anticoagulated patients due to the risk of spinal/epidural hematoma. Safe intervals between the last LMWH dose and neuraxial intervention (based on ASRA and SOAP guidelines) are summarized below.
| Regimen | Waiting interval before a neuraxial procedure |
|---|---|
| Prophylactic dose LMWH | ≥ 12 hours after last dose |
| Medium and therapeutic dose LMWH | ≥ 24 hours after last dose |
| Prophylactic / therapeutic UFH | After aPTT returns to normal (normalization may take up to 24 hours for subcutaneous therapeutic UFH) |
Practical approaches (UpToDate): (1) LMWH is continued and induction/cesarean section is planned at 39 weeks — low dose final injection given 12 hours before the procedure, medium/therapeutic dose 24 hours before the procedure; (2) or by switching from LMWH to UFH at approximately the 36th week, peripartum control is facilitated. If spontaneous labor begins, LMWH is discontinued immediately. Anticoagulation is restarted postpartum, 4–6 hours after vaginal birth and 6–12 hours after cesarean section (if there is no significant bleeding or traumatic catheter). A subanalysis of the Highlow study showed that 82% of patients on low-dose LMWH (93% in planned labor) were amenable to neuraxial intervention at the onset of unplanned labor.
Since D-dimer increases physiologically during pregnancy, its diagnostic value alone is limited; Diagnosis is based on imaging.
Some anticoagulants are avoided in pregnancy for fetal safety reasons:
Fondaparinux in breastfeeding: there is a difference between institutions. ASH 2018 Recommendation 12 lists certain agents, including UFH, LMWH, warfarin, and fondaparinux, as safe options in breastfeeding women requiring anticoagulation; The recommendation is strong, the evidence of effect is less certain. On the other hand, Ministry of Health 2026, printed p.13 states that fondaparinux should not be used in lactating mothers. These two suggestions are not the same; Agent selection is made by the relevant expert and national/institutional protocol. Avoidance of DOACs in breastfeeding is included in both sources. (Ministry of Health, 2026) (ASH, 2018)
September 2026 RCOG interim update changed prophylaxis doses based on BMI ≥50, interim risk score/durations, and weight. The Ministry of Health's 2026 national guide was published with a separate score and duration table. Therefore, the statement “threshold scores and doses unchanged” does not represent these versions. (Ministry of Health, 2026) (RCOG, September 2026)
While the full new edition of RCOG 37a is being prepared, the 2015 guideline (PDF with 2023 corrections) is used together with the September 2026 Position Statement. The position statement includes the new score and dose table; The 2015 table alone should not be presented under a current RCOG label. There is also guidance on NHS England Maternal Care Bundle recommendations for the management of those experiencing first trimester miscarriage/termination; These issues do not equate to a simple ongoing pregnancy/puerperium score. ( RCOG, September 2026 ) ( RCOG, 2015/2023 )
NIHR Health Technology Assessment synthesis (Davis et al., Health Technol Assess 2024;28(9); PMID 38476084) systematically compiled and decision-analytic modeling of 17 studies and 19 externally validated models in pregnancy/puerperium. The sensitivity of the models varies between 0-100% and the specificity varies between 5-100%; most have high/unclear bias. The most critical finding: the real source of decision uncertainty is not which model is chosen, but the lack of direct evidence for the effectiveness of thromboprophylaxis in preventing VTE in pregnancy/puerperium; The recommendations are based largely on indirect evidence. The analysis revealed that the most valuable study in the future will be an RCT of thromboprophylaxis versus placebo in obese puerperants.
The first concrete step to address this gap was the PP-HEP pilot RCT (Blondon et al., BJOG 2024;132(1):35-43; PMID 39238110): compared enoxaparin 40-60 mg/day × 10 days in 77 moderate-risk puerperants; A large multinational RCT was shown to be feasible, with the participation rate being significantly higher than in the North American trials (no VTE events at 3 months; bleeding signal in the prophylaxis arm). It is a proof of feasibility, not effectiveness.
The information that D-dimer increases physiologically during pregnancy and is not diagnostic by itself is valid; however, the current synthesis (CHEST 2025) highlights that two prospective studies (CT-PE/Righini 2018 and ARTEMIS 2019) have prospectively shown for the first time that the negative D-dimer + clinical prediction rule safely excludes PE without chest imaging.
Pregnancy-adjusted YEARS (ARTEMIS): Three criteria—clinical evidence of DVT, hemoptysis, PE being the most likely diagnosis—are questioned. PE is excluded if the threshold D-dimer is <1000 ng/mL if there is none, and <500 ng/mL if there are ≥1 criteria; In case of DVT, compression ultrasound is performed first. In ARTEMIS, this algorithm made CT pulmonary angiography unnecessary in ~39% of cases (van der Pol et al., N Engl J Med 2019;380:1139-1149). Attention: ~39% belongs to ARTEMIS; The trimester-related rates of 65% (1st trimester) / 32% (3rd trimester) belong to a separate study (CT-PE/Righini) and should not be confused.
Multicenter retrospective series accumulated in 2024-2025 in antithrombin deficiency, the highest-risk thrombophilia; LMWH with anti-Xa monitoring and peripartum antithrombin concentrate management in selected cases are being evaluated, but the optimal regimen is still at the expert consensus/case series level, with no new RCTs (JTH 2025; Thromb Res 2024). The practical approach remains co-management with hematology.
Finally, inter-guideline inconsistency was formally documented in 2025: a comparison of international guidelines for postpartum VTE prophylaxis showed that different guidelines lead to different prophylaxis decisions in the same patient (PMID 39939968, 2025) — confirming the structural reason behind variable prophylaxis rates.
Last updated: . This clinical update covers the differences in risk scores, duration, and prophylaxis dosing between the Ministry of Health 2026 and RCOG September 2026 guidelines.