Platelet Count (Whole Blood)
A small physiologic decrease in platelet count is expected during normal pregnancy due to hemodilution, increased plasma volume, and accelerated platelet clearance.
| Units | Nonpregnant Adult | 1st Trimester | 2nd Trimester | 3rd Trimester |
|---|---|---|---|---|
| ×10⁹/L (×10³/µL) | 150 – 400 | 174 – 391 | 155 – 409 | 146 – 429 |
Pregnancy Physiology
- Plasma volume expansion leads to dilutional decrease in platelet concentration.
- Increased platelet turnover results from enhanced splenic activity.
- Gestational thrombocytopenia occurs in 5–10% of pregnancies and is usually mild.
- Platelets often decline progressively across gestation with a nadir near term.
- Values ≥ 100 ×10⁹/L are typically compatible with normal pregnancy physiology.
Causes of LOW Platelet Count (Thrombocytopenia)
- Gestational thrombocytopenia (most common)
- Preeclampsia or HELLP syndrome
- Immune thrombocytopenic purpura (ITP)
- Systemic lupus erythematosus or antiphospholipid syndrome
- HIV infection
- Vitamin B12 or folate deficiency
- Massive transfusion
- Thrombotic thrombocytopenic purpura / HUS
- Sepsis or disseminated intravascular coagulation
- Hypersplenism
- Bone marrow disorders (aplastic anemia, leukemia)
- Medications (heparin, TMP-SMX, valproic acid, phenytoin, ranitidine)
Causes of HIGH Platelet Count (Thrombocytosis)
- Myeloproliferative neoplasms (ET, CML, myelofibrosis, polycythemia vera)
- Reactive thrombocytosis (most common):
- Acute blood loss
- Postpartum rebound
- Iron deficiency
- Infection or inflammation
- Hyposplenism or splenectomy
References
- Abbassi-Ghanavati M, Greer LG, Cunningham FG. Obstet Gynecol. 2009;114:1326–31.