Physiological Leukocytosis of Pregnancy: This condition is characterized by a mild to moderate increase in white blood cell count during pregnancy, which can be seen as early as the first trimester. The absence of symptoms and the presence of a mildly elevated WBC count with a predominance of neutrophils in a pregnant woman make this a likely diagnosis.

Urinary Tract Infection (UTI): Although the patient is asymptomatic, UTIs are common in pregnancy due to physiological changes that can predispose to infection. The elevated WBC count could be indicative of an underlying infection.
Viral Infection: Mild viral infections can cause a slight elevation in WBC count. Given the patient's age and pregnancy status, it's possible she might have a viral infection that is not causing significant symptoms.

Preeclampsia: Although typically associated with hypertension and proteinuria, preeclampsia can sometimes present with atypical features, including changes in blood cell counts. Early detection is crucial for the management of this condition.
Chorioamnionitis: An intrauterine infection that can be asymptomatic but may present with an elevated WBC count. It's a serious condition that requires prompt diagnosis and treatment to prevent adverse outcomes.
Leukemia: Although rare, leukemia can present with an elevated WBC count. Given the potential severity of this diagnosis, it's essential to consider it, even in the absence of other symptoms.

Myeloproliferative Neoplasms: Conditions like essential thrombocythemia or polycythemia vera can present with elevated platelet counts and sometimes an elevated WBC count. These are rare but important to consider due to their potential impact on pregnancy and maternal health.
Parvovirus B19 Infection: This viral infection can cause a mild increase in WBC count and is particularly relevant in pregnancy due to the risk of fetal hydrops and other complications.