Clinical Resources for Clinicians · For clinicians
When to Refer to Hematology: A Checklist for OB/GYNs
Refer to hematology when a blood abnormality is unexplained, fails first-line treatment, involves more than one cell line, or changes delivery or surgical planning. In OB/GYN practice the common triggers are iron-refractory anemia, suspected bleeding disorders, persistent or significant thrombocytopenia, VTE or high-risk thrombophilia, and hemoglobinopathies. Uncomplicated iron deficiency that responds to treatment usually doesn't need a referral; it needs fast access to IV iron.
The checklist below is built for the moment you're looking at an abnormal result and deciding whether this is a curbside, a referral, or a phone call today.
How to read the tiers
Each criterion is labeled emergency (direct to hospital), urgent (same-day or next-day discussion), expedited (within 1–2 weeks, sooner in late pregnancy), or routine. Then adjust for gestational age: a routine issue at 12 weeks can be urgent at 36.
Anemia
| Criterion | Priority |
|---|---|
| Severe or symptomatic anemia (dyspnea at rest, tachycardia, syncope) | Urgent: assess for admission or transfusion |
| Anemia with abnormal WBC or platelets, or blasts/abnormal cells on smear | Urgent |
| Signs of hemolysis (raised LDH and bilirubin, low haptoglobin, reticulocytosis) | Urgent to expedited |
| No hemoglobin response to IV iron | Expedited |
| Microcytosis with normal ferritin and inconclusive electrophoresis | Routine (expedited if partner is a carrier) |
| Macrocytic anemia not explained by B12/folate | Expedited |
| Iron deficiency with no apparent cause, in a non-menstruating or postmenopausal patient | Expedited; also needs a GI evaluation |
| Recurrent iron deficiency despite repletion | Routine |
| Patient declines blood products | Expedited in pregnancy, for early optimization |
Usually not needed: uncomplicated iron deficiency anemia that responds to oral or IV iron. What slows these patients down in practice isn't the absence of a consult; it's the wait for an infusion chair. See the outpatient anemia protocol.
Bleeding
| Criterion | Priority |
|---|---|
| Positive ACOG bleeding screen (HMB since menarche; PPH, surgical or dental bleeding; or ≥ 2 minor symptoms) | Routine to expedited |
| VWF < 0.50 IU/mL or abnormal coagulation studies | Expedited |
| Known bleeding disorder in pregnancy (VWD, hemophilia carrier, factor XI, platelet function disorder) | Expedited; by the second trimester for delivery planning |
| Unexplained postpartum hemorrhage or surgical bleeding | Routine (after recovery) |
| Adolescent with HMB at menarche or HMB needing transfusion | Expedited |
The bleeding history is the step most often skipped in a busy clinic, and it's the one that finds VWD. Details: HMB bleeding-disorder workup and VWD in pregnancy.
Platelets
| Criterion | Priority |
|---|---|
| Platelets < 50 × 10⁹/L at any point | Urgent |
| Thrombocytopenia with microangiopathic hemolysis, neurologic signs or renal injury (consider TTP/HUS) | Emergency |
| Platelets persistently < 100 × 10⁹/L, or first detected in first or early second trimester | Expedited |
| Platelets < 70 × 10⁹/L approaching delivery (neuraxial planning, per SOAP 2021) | Expedited, with anesthesia |
| Known ITP | Expedited: joint antenatal plan |
| Prior pregnancy with fetal/neonatal alloimmune thrombocytopenia | Expedited: MFM and hematology |
| Thrombocytosis persistently > 450 × 10⁹/L without reactive cause | Routine |
Mild thrombocytopenia late in pregnancy is usually gestational. The pattern that should make you pause is an early-pregnancy onset or a steady downward trend. See thrombocytopenia in pregnancy.
Thrombosis and anticoagulation
| Criterion | Priority |
|---|---|
| Acute VTE in pregnancy or postpartum | Urgent: start anticoagulation; co-manage |
| Mechanical heart valve | Urgent at first visit: cardiology, MFM and hematology |
| Prior VTE, planning pregnancy or newly pregnant | Expedited |
| High-risk thrombophilia (antithrombin deficiency, homozygous FVL or prothrombin variant, compound heterozygosity) | Expedited |
| Antiphospholipid syndrome | Expedited, with MFM and rheumatology |
| Thrombophilia testing questions | Routine |
| Heparin allergy or suspected HIT | Urgent |
Background: thrombophilia testing and VTE prophylaxis and anticoagulation in pregnancy.
Hemoglobinopathies
| Criterion | Priority |
|---|---|
| Sickle cell disease (HbSS, HbSC, HbS-β-thalassemia) in pregnancy | Expedited: co-management throughout |
| Beta-thalassemia intermedia/major or HbH disease | Expedited |
| Both partners carriers of a significant hemoglobinopathy | Expedited: genetics/MFM; hematology as needed |
In practices serving communities with higher carrier rates, these referrals come up regularly. See sickle cell disease in pregnancy.
Other triggers
- Known hematologic malignancy, current or past, in pregnancy or planning pregnancy
- Lymphadenopathy, splenomegaly or B symptoms with abnormal counts
- Persistently raised hemoglobin or hematocrit, suggesting polycythemia
- Neutropenia that doesn't fit benign ethnic neutropenia or a drug effect
- Prior bariatric surgery with recurrent multifactorial anemia; see anemia after bariatric surgery
Gestational age changes everything
- First trimester: time to complete a workup, finish an oral iron trial and plan. Routine or expedited tiers fit most issues.
- Second trimester: the best window for hematology input on delivery planning (bleeding disorders, anticoagulation, hemoglobinopathies) and for IV iron when oral iron has failed.
- Third trimester: anything that could affect delivery (anemia, platelets, VWF levels, anticoagulant timing) is expedited at minimum. After about 34 weeks, a two-week delay can mean the plan isn't ready when labor starts.
- Postpartum: reassess anything attributed to pregnancy, such as thrombocytopenia that doesn't resolve or anemia that persists despite treatment. After unexplained PPH, refer for a bleeding-disorder evaluation once the patient has recovered.
Gynecology referrals
Not every hematology question in an OB/GYN practice is obstetric:
- HMB with a positive bleeding screen or abnormal VWF studies
- Iron deficiency that keeps coming back despite treatment of HMB
- Preoperative evaluation before hysterectomy, myomectomy or ablation with a suspicious bleeding history
- Thrombophilia or prior VTE when choosing contraception or menopausal hormone therapy
- Iron deficiency anemia in postmenopausal patients, which also needs GI evaluation
Before you refer: four quick checks
- Is the abnormality confirmed on a repeat sample (for example, excluding platelet clumping)?
- Have the simple causes been checked: ferritin, B12, folate, medications?
- Would a hematology evaluation change management now or at delivery?
- Does the patient need a treatment, like IV iron, more than a consultation?
Many questions (a borderline ferritin, whether a platelet trend needs a visit, which IV iron product) are answered faster by a five-minute clinician-to-clinician conversation than by a referral.
What to send
A good packet means the first visit can make decisions:
- The specific question ("Delivery plan for type 1 VWD at 20 weeks," not "anemia")
- Gestational age and EDD, with planned delivery site
- Labs: CBC trend with indices, ferritin and TSAT, smear if done, coagulation studies, hemoglobinopathy results
- Treatment so far: iron products, doses, dates, response
- History: bleeding, VTE, family history, prior pregnancies, transfusions
- Medications, including anticoagulants and antiplatelets
- Urgency and the best contact for the OB clinician
Practice-level systems: setting up a hematology referral workflow.
Referral partnership in New York
Some of these criteria call for a full consult; others mainly need fast access to treatment. Premier Hematology & Oncology, which sponsors our professional resources, offers OB/GYN practices referral pathways for both, along with IV iron infusions and co-management, at sites across New York City, Long Island and the Hudson Valley. See our hematology partners page.
Frequently asked questions
Does every pregnant patient with anemia need a hematology referral?
No. Uncomplicated iron deficiency anemia that responds to oral or IV iron can be managed by the obstetric team. Refer when anemia is unexplained, does not respond to iron, or comes with other abnormal counts.
What platelet count in pregnancy should prompt hematology referral?
Mild thrombocytopenia late in pregnancy is usually gestational. Consider hematology input for counts persistently below about 100 × 10⁹/L, counts below 70 × 10⁹/L near delivery, early-pregnancy onset, bleeding, or other abnormal cell lines.
Should patients on anticoagulation in pregnancy see hematology?
Patients with prior VTE, high-risk thrombophilia, antiphospholipid syndrome or mechanical heart valves benefit from hematology co-management, especially for peripartum planning.
Sources
- ACOG — Anemia in Pregnancy (Practice Bulletin No. 233)
- ACOG — Thrombocytopenia in Pregnancy (Practice Bulletin No. 207)
- ACOG — Thromboembolism in Pregnancy (Practice Bulletin No. 196)
- ACOG — Inherited Thrombophilias in Pregnancy (Practice Bulletin No. 197)
- ACOG — Screening and Management of Bleeding Disorders in Adolescents With Heavy Menstrual Bleeding (Committee Opinion No. 785)
- SOAP — Interdisciplinary Consensus Statement on Neuraxial Procedures in Obstetric Patients With Thrombocytopenia (2021)
- ASH — 2018 guidelines for management of venous thromboembolism: venous thromboembolism in the context of pregnancy
This article is for general education and is not medical advice. It does not replace an evaluation by a licensed clinician who knows your history. If you think you have a medical emergency, call 911.