Risk Signs and Complications During Pregnancy

Why Recognizing Warning Signs Matters

The CDC reports that approximately 700 women die each year in the United States from pregnancy-related complications — and a significant proportion of those deaths are considered preventable with timely medical care. The major preventable killers are hemorrhage, infection, preeclampsia, and pulmonary embolism. Every one of them announces itself with specific symptoms before it becomes catastrophic. Recognizing those symptoms is what separates a managed complication from a tragedy.

The practical challenge is telling the difference between normal pregnancy discomfort — round ligament pain, swollen ankles at the end of the day, occasional Braxton Hicks contractions — and the small subset of symptoms that require urgent action. This guide walks through the most clinically important warning signs, trimester by trimester, alongside the major complications you need to understand before they arise.

The American College of Obstetricians and Gynecologists (ACOG) is explicit on this point: when in doubt, call. No provider has ever regretted a patient calling about a symptom that turned out to be benign. The same cannot be said for the reverse.

First Trimester Warning Signs (Weeks 1–13)

Roughly 10–15% of clinically recognized pregnancies end in miscarriage in the first trimester, most due to chromosomal abnormalities. Light spotting around implantation (5–10 days after conception) can be normal, but any bleeding requires a conversation with your provider — because the symptom that looks like a minor bleed can occasionally be the first sign of an ectopic pregnancy, which kills.

Symptoms that require same-day evaluation in the first trimester:

• Heavy vaginal bleeding — heavier than a period, especially with cramping or passing tissue. This may indicate a miscarriage in progress or, critically, an ectopic pregnancy.
• One-sided sharp pelvic pain — particularly if accompanied by vaginal bleeding, dizziness, or shoulder tip pain, this is the classic presentation of a ruptured ectopic pregnancy, a life-threatening surgical emergency. Ectopic pregnancy affects roughly 1–2% of all pregnancies and is the leading cause of first-trimester maternal death.
• Severe nausea and vomiting with inability to keep down fluids — hyperemesis gravidarum affects 0.3–3% of pregnancies and causes dangerous dehydration, electrolyte imbalances, and weight loss requiring IV fluids and antiemetic treatment.
• Fever above 38°C / 100.4°F — fever in early pregnancy signals infection; a UTI progressing to pyelonephritis is common in pregnancy, and some infections carry teratogenic risk.
• Burning or pain with urination — urinary tract infections are far more common during pregnancy due to physiologic changes in the urinary tract. Untreated UTI progresses rapidly to kidney infection and is an established trigger for preterm labor.

Mild nausea (morning sickness), breast tenderness, fatigue, and light pelvic pressure are all expected in the first trimester and do not require urgent evaluation unless they are severe or rapidly worsening.

Second Trimester Warning Signs (Weeks 14–27)

Morning sickness typically resolves by week 14, the miscarriage rate drops sharply after the first trimester, and most women feel the baby move for the first time. But several serious complications can emerge during this window — and they are easy to miss because the second trimester feels like smooth sailing. Awareness of the early warning signs is what changes outcomes.

Call your provider promptly or go to the ER for:

• Vaginal bleeding of any amount — second-trimester bleeding is never "normal." Causes include placenta previa (the placenta covering the cervix), placental abruption (placenta separating from the uterine wall), and cervical incompetence (painless dilation of the cervix before term).
• Gush or steady trickle of fluid from the vagina — this may indicate preterm premature rupture of membranes (PPROM). Amniotic fluid is typically clear and odorless; it does not stop when you contract your pelvic floor muscles the way urine does.
• Regular uterine contractions before 37 weeks — contractions every 10 minutes or more frequently for an hour or more, especially if accompanied by pelvic pressure, lower back pain, or a change in discharge, require evaluation for preterm labor.
• Sudden severe abdominal pain — in the second trimester, this can indicate placental abruption, appendicitis (which is harder to diagnose in pregnancy because the appendix shifts position as the uterus grows), or ovarian torsion.
• Decreased or absent fetal movement after 28 weeks — fetal movements are not reliably felt before 24–25 weeks, but any perceived decrease in your baby's established movement pattern warrants evaluation. The standard approach is a kick count followed by a non-stress test if 10 movements are not felt in two hours.
• Persistent severe headache or visual disturbances — tension headaches are common in pregnancy, but a headache that is severe, sudden, or accompanied by blurred vision, seeing spots, or light sensitivity is an early sign of preeclampsia, which can develop as early as 20 weeks.

Third Trimester Warning Signs (Weeks 28–40+)

Preeclampsia peaks in the third trimester. Preterm labor is most consequential after 28 weeks, when survival rates are high but outcomes are still heavily dependent on how early delivery occurs. Placental complications become more likely as the placenta ages. This is the trimester where knowing which symptoms are emergencies — and acting on that knowledge fast — matters most.

Seek emergency care immediately for any of the following:

• Sudden severe headache — particularly occipital or frontal, unresponsive to acetaminophen, in the context of elevated blood pressure.
• Vision changes — blurred vision, seeing spots or flashing lights, or temporary loss of vision. These are neurological manifestations of severe preeclampsia (and of HELLP syndrome when liver enzymes and platelet count are also involved).
• Upper right abdominal or shoulder pain — pain under the right rib cage or referred to the right shoulder indicates hepatic capsule distension from preeclampsia with severe features or HELLP syndrome.
• Sudden severe swelling of the face, hands, or feet — mild ankle swelling at the end of the day is common in late pregnancy. Sudden, asymmetric, or facial swelling — particularly combined with other symptoms — is not.
• Difficulty breathing or chest pain — pulmonary embolism is a major cause of maternal mortality. Pregnant and postpartum women are at 4–5 times higher risk of VTE than non-pregnant women; symptoms include sudden shortness of breath, chest pain, and rapid heart rate.
• Absent or dramatically reduced fetal movement — if a kick count does not yield 10 movements in 2 hours, go to labor and delivery. Do not wait for morning.
• Heavy vaginal bleeding — third-trimester hemorrhage most commonly indicates placenta previa or placental abruption, both of which can escalate within minutes.

Preeclampsia: What You Need to Know

Preeclampsia is a pregnancy-specific disorder characterized by new-onset hypertension and either proteinuria or end-organ dysfunction after 20 weeks of gestation. It affects 2–8% of all pregnancies globally and is a leading cause of maternal and perinatal morbidity and mortality.

ACOG diagnostic criteria: A systolic blood pressure of 140 mmHg or higher, or a diastolic of 90 mmHg or higher, on two separate readings at least four hours apart, after 20 weeks in a previously normotensive woman, plus proteinuria (300 mg/24h or protein:creatinine ratio of 0.3) or in the absence of proteinuria, new-onset thrombocytopenia (platelets under 100,000/microliter), renal insufficiency (creatinine above 1.1 mg/dL), impaired liver function, pulmonary edema, or new-onset headache unresponsive to medication.

Severe features include systolic BP of 160 or higher, diastolic BP of 110 or higher, thrombocytopenia, impaired liver function with severe right upper-quadrant pain, progressive renal insufficiency, pulmonary edema, or new-onset headache unresponsive to medication and not accounted for by other diagnoses. Preeclampsia with severe features requires hospitalization.

Prevention: ACOG and the US Preventive Services Task Force now recommend low-dose aspirin (81 mg/day) beginning at 12–28 weeks (optimally before 16 weeks) for women at high risk — those with a history of preeclampsia, multifetal pregnancy, chronic hypertension, type 1 or 2 diabetes, kidney disease, or autoimmune conditions. The number needed to treat to prevent one case of preterm preeclampsia with aspirin is approximately 30.

The only definitive treatment for preeclampsia is delivery. Management depends on gestational age and severity. Magnesium sulfate is used to prevent eclamptic seizures in women with severe features. Women with a history of preeclampsia carry a substantially elevated lifetime cardiovascular risk and should be monitored accordingly.

Gestational Diabetes: Screening, Diagnosis, and Management

Gestational diabetes mellitus (GDM) is defined as glucose intolerance first diagnosed in the second or third trimester of pregnancy that is not clearly overt pre-existing diabetes. It affects approximately 6–9% of pregnancies in the US (CDC), with higher rates among women of South Asian, East Asian, Hispanic, and Black ancestry.

Screening and diagnosis: ACOG recommends universal screening for GDM at 24–28 weeks using either a two-step approach (1-hour 50g glucose challenge test; if result is 130–140 mg/dL or above, proceed to a 3-hour 100g OGTT) or a one-step approach (2-hour 75g OGTT with IADPSG criteria). The two-step approach is more common in the US. Women with risk factors — obesity, prior GDM, prior macrosomic infant, strong family history of type 2 diabetes, or polycystic ovary syndrome — may be screened earlier in pregnancy.

Why it matters: Poorly controlled GDM is associated with fetal macrosomia (large for gestational age), shoulder dystocia during delivery, neonatal hypoglycemia, increased rates of cesarean delivery, and a higher lifetime risk of type 2 diabetes for both mother and child. Well-managed GDM, however, typically results in outcomes comparable to the general obstetric population.

Management: The first-line treatment is medical nutrition therapy (a carbohydrate-controlled diet with attention to glycemic index) combined with regular moderate-intensity physical activity. If fasting glucose exceeds 95 mg/dL or postprandial targets are not met after 1–2 weeks of lifestyle modification, insulin therapy or oral agents (metformin or glyburide, though insulin remains the preferred agent) are initiated. Blood glucose targets are fasting under 95 mg/dL, one-hour postprandial under 140 mg/dL, and two-hour postprandial under 120 mg/dL.

After delivery, women with GDM should undergo a 75g two-hour OGTT at 4–12 weeks postpartum to screen for persistent impaired glucose tolerance or type 2 diabetes, and annually thereafter per ADA guidelines.

Preterm Labor: Signs, Risk Factors, and What Happens Next

Preterm birth — delivery before 37 completed weeks of gestation — occurs in approximately 10% of births in the US (CDC data) and is the leading cause of neonatal morbidity and mortality. Spontaneous preterm labor accounts for roughly half of preterm births; the remainder are medically indicated deliveries due to maternal or fetal conditions.

Warning signs of preterm labor:

• Regular contractions — 4 or more in 20 minutes, or 8 or more in 60 minutes — before 37 weeks
• Lower back pain, especially if rhythmic or new-onset
• Pelvic pressure (the sensation of the baby "pushing down")
• Abdominal cramping, with or without diarrhea
• Change in vaginal discharge — increased volume, watery, mucous, or blood-tinged (loss of mucus plug)
• Fluid leaking from the vagina (possible rupture of membranes)

If you have any of these symptoms before 37 weeks, go to labor and delivery immediately. Evaluation includes a cervical exam, fetal fibronectin test (a biomarker that predicts preterm delivery risk within 7–14 days), and transvaginal cervical length measurement by ultrasound.

If preterm delivery appears imminent before 34 weeks: A course of antenatal corticosteroids (betamethasone or dexamethasone) is given to accelerate fetal lung maturity. A single rescue course may be given between 34 and 36+6 weeks if delivery is expected within 7 days and no prior course was given in the preceding 14 days. Magnesium sulfate is given before 32 weeks for fetal neuroprotection. Tocolytics (medications to slow contractions) are used short-term to allow time for these treatments.

Risk factors for spontaneous preterm birth include prior preterm birth (the strongest single predictor), short cervical length on mid-trimester ultrasound, multiple gestation, uterine anomalies, prior cervical procedures, low pre-pregnancy BMI, smoking, and substance use. Women with prior preterm birth and a short cervix may be candidates for 17-alpha hydroxyprogesterone supplementation or cervical cerclage.

Placental Complications: Previa and Abruption

Placenta previa occurs when the placenta implants over or near the internal cervical os. Complete previa (placenta fully covering the os) is found in roughly 1 in 200 pregnancies at term, while partial or marginal previa is more common. The hallmark is painless, bright-red vaginal bleeding in the second or third trimester. Women with placenta previa are placed on pelvic rest (nothing in the vagina), told to avoid strenuous activity, and delivered by cesarean — typically at 36–37 weeks for complete previa. Many cases diagnosed in the second trimester resolve spontaneously as the uterus grows.

Placental abruption — premature separation of the normally implanted placenta — affects 1% of pregnancies and is the most common cause of third-trimester bleeding. It presents with painful vaginal bleeding and uterine rigidity or tenderness; in concealed abruption, there is no external bleeding but severe abdominal pain and a board-hard uterus. Risk factors include hypertension, prior abruption, trauma, cocaine use, and smoking. Severe abruption causes rapid fetal distress and can trigger disseminated intravascular coagulation (DIC) in the mother; emergency delivery is required.

Placenta accreta spectrum (accreta, increta, percreta) — abnormal placental implantation into or through the uterine wall — is increasingly common due to rising cesarean rates. It is typically identified on ultrasound and MRI during prenatal care and managed with a planned cesarean delivery at a facility equipped for massive transfusion and, often, hysterectomy.

Other Important Complications to Know

Venous thromboembolism (VTE): Pregnancy increases the risk of deep vein thrombosis and pulmonary embolism 4–5 fold. Signs of DVT include unilateral leg swelling, pain, warmth, and redness. Signs of pulmonary embolism include sudden shortness of breath, chest pain, and rapid heart rate. Both require emergency evaluation. Women with prior VTE, thrombophilia, or prolonged immobility may require anticoagulation during pregnancy.

Intrahepatic cholestasis of pregnancy (ICP): A liver disorder of pregnancy characterized by intense itching — particularly of the palms and soles, often worse at night — without a rash, plus elevated bile acids in the blood. It typically appears in the third trimester and resolves after delivery. ICP carries an increased risk of stillbirth, particularly when total bile acids exceed 100 micromol/L. Management includes ursodeoxycholic acid and, usually, induction of labor at 36–37 weeks.

Recurrent urinary tract infections: Asymptomatic bacteriuria occurs in 2–7% of pregnancies and, if untreated, progresses to symptomatic UTI or pyelonephritis in 20–30% of cases. ACOG recommends universal screening at the first prenatal visit and treatment of any positive urine culture, regardless of symptoms.

Peripartum cardiomyopathy: A rare but serious form of heart failure that develops in the last month of pregnancy or within five months of delivery in the absence of prior heart disease. Symptoms include breathlessness, fatigue, leg swelling, and reduced exercise tolerance. It requires prompt cardiology referral and management with heart failure therapy modified for pregnancy safety.

When to Call Your OB vs. Go to the ER

A practical guide to triage:

Call 911 or go directly to the ER (do not wait for a callback):

• Heavy vaginal bleeding (soaking more than one pad per hour)
• Sudden severe headache unlike any headache you have had before
• Vision loss, severe blurring, or persistent seeing-spots
• Difficulty breathing or chest pain
• Signs of severe allergic reaction (anaphylaxis)
• Suspected ruptured ectopic pregnancy: one-sided sharp pain + bleeding + dizziness/fainting
• Severe abdominal pain, rigid uterus, or suspected abruption
• Seizure
• Fever above 39°C / 102.2°F with rigors

Call your OB/midwife or triage line same day:

• Any vaginal bleeding (light to moderate) in the second or third trimester
• Fluid leaking from the vagina
• Regular contractions before 37 weeks
• Reduced fetal movement after 28 weeks (try kick counts first)
• Swelling that is sudden, severe, or affects the face
• Blood pressure reading of 140/90 or higher on a home cuff
• Moderate persistent headache with or without visual symptoms
• Fever of 38°C / 100.4°F or above
• Signs of UTI: burning, frequency, low back pain
• Intense itching of the palms/soles, especially at night (possible ICP)

If a symptom is causing you significant concern, call your provider. A brief nurse or midwife phone triage takes three minutes and can immediately distinguish a reassuring finding from one that needs urgent evaluation — it is always worth making the call.

Frequently Asked Questions