Passing small blood clots vaginally during pregnancy can happen, particularly in the first trimester, but it is not something to dismiss without understanding the cause. The term “blood clots during pregnancy” actually covers two very different situations: vaginal bleeding with clots, which may or may not signal a problem, and blood clots forming inside your veins, which is a medical emergency. Both deserve attention, and knowing the difference matters.
Vaginal Blood Clots in Early Pregnancy
Up to 25% of pregnant women experience some vaginal bleeding in the first trimester. Sometimes that bleeding includes small clots. Light spotting or minor clotting can result from the embryo implanting into the uterine wall, cervical sensitivity from increased blood flow, or minor hormonal shifts. In many of these cases, the pregnancy continues without complications.
However, heavier bleeding with clots can point to something that needs medical evaluation. One common cause is a subchorionic hematoma, which occurs when the membrane surrounding the embryo partially separates from the uterine wall. This creates a pocket of blood that can cause vaginal bleeding, sometimes heavy and with visible clots. Small hematomas with minimal bleeding rarely pose a problem and often resolve on their own. Larger ones may place the pregnancy at higher risk for complications including miscarriage and placental abruption.
The size and volume of clots you’re passing matters. As a general guideline from the NHS, you should seek emergency evaluation if you are soaking through more than two large pads per hour or passing clots the size of your palm. Clots smaller than that still warrant a call to your midwife or provider, especially if the bleeding is persistent, accompanied by cramping, or happens alongside dizziness or lightheadedness.
Why Pregnancy Makes Your Blood Clot More Easily
Pregnancy fundamentally changes how your blood clots. Your body increases production of several clotting proteins, including fibrinogen and factors VII, VIII, and X. At the same time, protein S, which normally helps keep clotting in check, drops significantly. Your body also produces five times the normal amount of a substance that blocks the breakdown of clots. All of these shifts push your blood toward clotting more readily.
This is actually by design. Your body is preparing to prevent excessive bleeding during delivery. But the trade-off is a higher risk of clots forming where they shouldn’t, specifically inside your deep veins. This hypercoagulable state persists throughout pregnancy and continues for up to three months after delivery.
Blood Clots in Your Veins: A Different Problem
Venous thromboembolism, a clot forming in a deep vein, occurs in roughly 1.7 out of every 1,000 deliveries. That makes it uncommon but not rare, and it remains one of the leading causes of pregnancy-related death. The risk is present throughout pregnancy, during childbirth, and for up to three months postpartum.
A deep vein clot typically forms in the leg, and the danger is that it can break loose and travel to the lungs. A clot in the lungs is called a pulmonary embolism and can be life-threatening.
Signs of a Deep Vein Clot
The classic symptoms involve one leg, not both. According to the NHS, watch for:
- Pain, swelling, and tenderness in one leg, usually in the calf, that worsens when you walk
- A heavy ache or warmth in the affected area
- Red or discolored skin, particularly at the back of the leg below the knee
If a clot has traveled to your lungs, symptoms shift to sudden shortness of breath, chest pain (especially when breathing deeply), rapid heartbeat, or coughing up blood. Any of these warrants immediate emergency care.
Who Faces the Highest Risk
The two strongest risk factors for developing a venous clot during pregnancy are a personal history of prior clots and inherited clotting disorders. Women with deficiencies in certain natural anticoagulant proteins, or those who carry two copies of the factor V Leiden gene mutation, face an absolute risk above 3%, well above the baseline.
Several other factors raise risk to a moderate degree: a BMI of 40 or higher, prolonged bed rest or immobility during pregnancy, hospital admission, surgery, and serious infections. Factors that create a smaller but still measurable increase include being over 35, having a BMI between 25 and 40, having had three or more pregnancies, smoking, IVF treatment, varicose veins, and a family history of clots. Pregnancy-specific conditions like severe morning sickness, carrying multiples, and preeclampsia also contribute a small amount of additional risk.
How Venous Clots Are Treated During Pregnancy
If you develop a clot during pregnancy, treatment centers on injectable blood thinners that do not cross the placenta. Multiple studies confirm these medications pose no documented risk to the fetus, which is why they are the first-line choice. They work by slowing your blood’s ability to form new clots while your body gradually dissolves the existing one.
Oral blood thinners like warfarin are avoided because they do cross the placenta. Exposure in the first trimester is linked to skeletal abnormalities in the developing baby, and use later in pregnancy is associated with neurological complications including seizures and developmental delays. Warfarin carries the FDA’s most restrictive pregnancy classification. Newer oral blood thinners also cross the placenta in animal and lab studies and are not used during pregnancy.
Near the end of pregnancy, typically around 36 weeks, your care team will adjust your medication to a shorter-acting form. This allows your clotting ability to normalize quickly enough for safe delivery and, if needed, an epidural. The timing of this transition is carefully managed to balance clot prevention with safe labor.
Reducing Your Risk
Staying mobile is one of the most effective things you can do. Prolonged sitting, whether from bed rest, a long flight, or a desk job, allows blood to pool in your legs. If you’re on a long journey, getting up to walk every hour or two and flexing your feet and ankles while seated helps keep blood moving. Staying well hydrated also supports healthy circulation.
If you have known risk factors, particularly a personal or strong family history of clots or a diagnosed clotting disorder, your provider may recommend preventive blood thinner injections during part or all of your pregnancy and into the postpartum period. Compression stockings are another common recommendation for women at elevated risk, helping push blood back up from the lower legs.
The postpartum period deserves as much attention as pregnancy itself. Your clotting risk stays elevated for up to three months after delivery, and the early weeks after a cesarean section carry particularly high risk due to reduced mobility during recovery. Staying aware of leg symptoms during this window is just as important as it was during pregnancy.