What Complications Can Happen During Each Stage of Pregnancy?

Pregnancy brings immense joy, but it also comes with real medical risks that deserve honest discussion. Understanding which complications are most common at different stages can help you recognize warning signs early and advocate for the care you need.

Every pregnancy is different, and most proceed without major issues. But knowing what to watch for at each trimester empowers you to get help quickly when something doesn’t feel right.

Complications That Can Occur in the First Trimester (Weeks 1 Through 13)

The first trimester is when the embryo undergoes its most dramatic development, forming all major organs and body systems. This also makes it a vulnerable period for certain complications.

Miscarriage in Early Pregnancy

Miscarriage, medically called spontaneous abortion, affects between 10% and 20% of known pregnancies. Most occur during the first trimester, often before many people even realize they’re pregnant.

The majority of first-trimester miscarriages happen because of chromosomal abnormalities in the embryo, which are random genetic errors that occur during cell division and prevent normal development. This isn’t something parents can prevent or predict.

Warning signs include vaginal bleeding (from light spotting to heavy flow), severe cramping, tissue passing from the vagina, or sudden disappearance of pregnancy symptoms. Not all bleeding means miscarriage, but any bleeding warrants a call to your healthcare provider.

Ectopic Pregnancy and Why It Requires Emergency Treatment

An ectopic pregnancy occurs when a fertilized egg implants somewhere outside the uterus, most commonly in a fallopian tube. The embryo cannot survive in this location, and as it grows, it poses life-threatening risks to the pregnant person.

If left untreated, an ectopic pregnancy can rupture the fallopian tube, causing severe internal bleeding. Symptoms include sharp abdominal or pelvic pain (especially on one side), vaginal bleeding, shoulder pain (from internal bleeding irritating the diaphragm), dizziness, or fainting.

Ectopic pregnancies require immediate medical intervention, typically through medication or surgery. Early detection through ultrasound and blood tests can catch these pregnancies before rupture occurs.

Hyperemesis Gravidarum and Severe Morning Sickness

While nausea and vomiting affect most pregnant people to some degree, hyperemesis gravidarum is an extreme form that causes severe, persistent vomiting leading to dehydration, weight loss (losing more than 5% of pre-pregnancy weight), and electrolyte imbalances.

Unlike typical morning sickness that improves with crackers and rest, hyperemesis gravidarum often requires medical treatment including IV fluids, anti-nausea medications, and sometimes hospitalization. The condition can make it impossible to keep down food or even water.

The exact cause isn’t fully understood, but it may relate to hormone levels, particularly human chorionic gonadotropin (hCG). Most cases improve by the second trimester, though some people experience symptoms throughout pregnancy.

Gestational Trophoblastic Disease and Molar Pregnancy

Gestational trophoblastic disease refers to a rare group of conditions where abnormal cells grow in the uterus after conception. A molar pregnancy is the most common type, occurring when placental tissue develops abnormally instead of forming a viable pregnancy.

In a complete molar pregnancy, no embryo forms at all. Only abnormal placental tissue is created. In a partial molar pregnancy, some fetal tissue may begin developing but cannot survive. Both require removal of the tissue, usually through a procedure called dilation and curettage (D&C).

Signs include vaginal bleeding, a uterus that’s larger than expected for gestational age, severe nausea, and abnormally high hCG levels. Most molar pregnancies are detected through ultrasound, which shows a characteristic “snowstorm” pattern instead of a developing embryo.

Urinary Tract Infections During Early Pregnancy

Pregnancy increases the risk of urinary tract infections (UTIs) because hormonal changes slow urine flow and the growing uterus can compress the bladder. If untreated, a simple UTI can progress to pyelonephritis, a serious kidney infection that can trigger preterm labor.

Symptoms include painful urination, frequent urge to urinate, cloudy or foul-smelling urine, pelvic pain, and sometimes fever or back pain. Many pregnant people have asymptomatic bacteriuria (bacteria in urine without symptoms), which is why prenatal urine tests are routine.

Prompt antibiotic treatment clears most UTIs and prevents them from becoming dangerous. Staying hydrated and urinating frequently also help reduce infection risk.

Complications That Develop in the Second Trimester (Weeks 14 Through 27)

The second trimester often feels easier physically, but it brings its own set of potential complications. This is when many screening tests occur because fetal growth becomes more apparent and certain conditions can now be detected.

Gestational Diabetes and Blood Sugar Problems During Pregnancy

Gestational diabetes develops when the body cannot produce enough insulin to handle the increased blood sugar demands of pregnancy. Hormones from the placenta can make cells more resistant to insulin, and some people’s pancreas cannot keep up with the extra need.

Most pregnant people are screened for gestational diabetes between 24 and 28 weeks through a glucose tolerance test. Those with risk factors like obesity, previous gestational diabetes, family history of diabetes, or certain ethnic backgrounds may be tested earlier.

Uncontrolled gestational diabetes increases risks for the baby, including excessive growth (macrosomia), low blood sugar after birth, breathing difficulties, and higher likelihood of developing diabetes later in life. For the pregnant person, it raises the chances of preeclampsia and needing a cesarean delivery.

Management typically involves blood sugar monitoring, dietary changes, regular exercise, and sometimes insulin or medication. Most cases resolve after delivery, but having gestational diabetes increases the risk of developing type 2 diabetes later.

Cervical Insufficiency and Risk of Preterm Birth

Cervical insufficiency, also called incompetent cervix, occurs when the cervix begins to open too early during pregnancy without contractions or labor pains. This typically happens in the second trimester and can lead to pregnancy loss or extremely preterm birth.

The condition often goes undetected until it causes problems because it doesn’t produce typical warning signs. Some people experience mild pressure, backache, light bleeding, or change in vaginal discharge, but many notice nothing until the cervix has already dilated significantly.

Women who have experienced second-trimester loss or preterm birth due to cervical insufficiency may be candidates for cervical cerclage, which is a procedure where the cervix is stitched closed during pregnancy. The stitch is removed near term to allow for delivery. Progesterone supplementation and regular ultrasound monitoring of cervical length also help manage this condition.

Preeclampsia and High Blood Pressure After 20 Weeks

Preeclampsia is a serious pregnancy complication characterized by high blood pressure combined with signs of organ damage, most often affecting the kidneys (shown by protein in urine) or liver. It typically develops after 20 weeks of pregnancy, though some people show earlier warning signs.

The condition affects approximately 4% of pregnancies in the United States and can progress rapidly from mild to severe. Risk factors include first pregnancy, previous preeclampsia, chronic hypertension, obesity, age over 35, multiple gestation (twins or more), and certain medical conditions like diabetes or kidney disease.

Warning signs include:

• Severe headaches that don’t respond to usual remedies
• Vision changes like blurred vision, seeing spots, or light sensitivity
• Upper abdominal pain, especially under the ribs on the right side
• Nausea or vomiting in the second or third trimester
• Sudden weight gain or swelling, particularly in the face and hands
• Decreased urine output

The only cure for preeclampsia is delivery of the baby. When diagnosed early enough that the baby is still very premature, doctors try to manage the condition with blood pressure medication, bed rest, and close monitoring to allow more time for fetal development. If the condition becomes severe, delivery becomes necessary regardless of gestational age to protect both mother and baby.

Placenta Previa and Bleeding from Low-Lying Placenta

Placenta previa occurs when the placenta partially or completely covers the cervix, the opening through which the baby would normally pass during delivery. This positioning creates a risk of severe bleeding, especially as the cervix begins to thin and open in preparation for labor.

The condition is usually detected during routine second-trimester ultrasounds. Many cases of partial placenta previa diagnosed early in the second trimester resolve on their own as the uterus grows and the placenta appears to “migrate” upward (though it’s actually the lower uterus stretching).

Complete placenta previa that persists into the third trimester typically requires cesarean delivery because vaginal birth would cause catastrophic bleeding. Warning signs include painless, bright red vaginal bleeding, often occurring suddenly. Any vaginal bleeding during pregnancy requires immediate medical evaluation.

Amniotic Fluid Disorders and Fetal Development

The amniotic fluid surrounding the baby serves crucial functions: cushioning the fetus, allowing movement for musculoskeletal development, and supporting lung development as the baby “breathes” the fluid. Both too little (oligohydramnios) and too much (polyhydramnios) amniotic fluid can signal problems.

Oligohydramnios can result from problems with the baby’s kidneys or urinary tract (since much of the amniotic fluid in later pregnancy comes from fetal urine), placental insufficiency, ruptured membranes, or certain medications. Low fluid levels can restrict fetal movement and lung development and increase the risk of umbilical cord compression.

Polyhydramnios often relates to maternal diabetes, fetal swallowing difficulties, certain birth defects (particularly of the digestive system or nervous system), or twin-to-twin transfusion syndrome in identical twins. Excessive fluid can cause maternal discomfort, preterm labor, or abnormal fetal positioning.

Both conditions are monitored through ultrasound measurements. Treatment depends on the underlying cause and severity but may include frequent monitoring, early delivery if the baby’s lungs are mature enough, or procedures to remove excess fluid.

Fetal Growth Restriction and Small Babies

Fetal growth restriction (FGR), also called intrauterine growth restriction (IUGR), means the baby is measuring smaller than expected for gestational age. This differs from babies who are simply constitutionally small but healthy. FGR indicates the fetus is not receiving adequate nutrition or oxygen to grow properly.

Causes include placental problems (the most common reason), maternal hypertension or preeclampsia, smoking, malnutrition, certain infections, or chromosomal abnormalities. Sometimes no cause is identified.

Doctors track fetal growth through measurement of the uterus externally and through ultrasound. When growth restriction is detected, monitoring increases to assess whether the baby is tolerating the environment. Tests include regular ultrasounds to measure the baby, Doppler ultrasounds to check blood flow, and non-stress tests to monitor the baby’s heart rate.

Management depends on severity and gestational age. In mild cases, the pregnancy may continue with close monitoring. In severe cases, especially if tests show the baby is no longer thriving, early delivery may be safer than continuing the pregnancy.

Complications That Happen in the Third Trimester (Weeks 28 Through Delivery)

The final stretch of pregnancy involves rapid fetal growth and preparation for birth. The sheer physical demands on your body increase, and complications during this period can affect both pregnancy and delivery.

Preterm Labor and Birth Before 37 Weeks

Preterm labor occurs when regular contractions begin causing the cervix to dilate before 37 weeks of pregnancy. Babies born preterm face higher risks of breathing problems, feeding difficulties, developmental delays, vision and hearing problems, and other complications, with risks increasing the earlier the birth occurs.

Warning signs include:

• Regular contractions (every 10 minutes or more frequently)
• Menstrual-like cramping
• Pelvic pressure feeling like the baby is pushing down
• Low, dull backache
• Increased vaginal discharge or change in discharge type
• Leaking fluid from the vagina

Risk factors include previous preterm birth, carrying multiples, certain uterine or cervical abnormalities, infections, chronic conditions like hypertension or diabetes, smoking, substance use, high stress, and inadequate prenatal care.

If caught early enough, medications can sometimes stop preterm labor. Corticosteroids can accelerate fetal lung development if delivery seems likely. Magnesium sulfate may protect the baby’s brain if birth is imminent. Sometimes, despite all interventions, preterm birth cannot be prevented.

Gestational Hypertension and Blood Pressure Problems

Gestational hypertension refers to high blood pressure that develops after 20 weeks of pregnancy without the organ damage or protein in urine seen with preeclampsia. About half of people with gestational hypertension will progress to preeclampsia, which is why close monitoring is essential.

The condition is diagnosed when blood pressure readings are consistently 140/90 mmHg or higher. While less immediately dangerous than preeclampsia, gestational hypertension still requires careful management because high blood pressure reduces blood flow to the placenta, potentially affecting fetal growth and increasing the risk of placental abruption.

Treatment may include blood pressure medication, increased prenatal visits, home blood pressure monitoring, and regular assessment for signs of progression to preeclampsia. Most cases resolve after delivery, though they indicate increased risk for hypertension later in life.

Placental Abruption and Emergency Bleeding

Placental abruption occurs when the placenta separates from the uterine wall before delivery. This is an emergency situation because the placenta is the baby’s only source of oxygen and nutrients. Complete abruption threatens both fetal and maternal life.

Symptoms typically include vaginal bleeding (though sometimes blood gets trapped behind the placenta and isn’t visible), severe abdominal pain that doesn’t go away between contractions, back pain, uterine tenderness, rapid contractions, and signs of fetal distress. In severe cases, the pregnant person may go into shock.

Risk factors include high blood pressure, previous abruption, abdominal trauma from accidents or domestic violence, smoking, cocaine use, rupture of membranes, and having many previous pregnancies. Treatment depends on severity and gestational age but often requires immediate delivery, typically by emergency cesarean section.

Labor and Delivery Complications

Even after a healthy pregnancy, complications can arise during labor and delivery itself. Understanding these possibilities helps you recognize when things aren’t progressing normally.

Abnormal fetal positioning, such as breech (feet or bottom first) or transverse (sideways), can make vaginal delivery difficult or impossible. While some providers are skilled at delivering breech babies vaginally, many breech presentations result in cesarean delivery to reduce risks to the baby.

Umbilical cord problems include cord prolapse (when the cord slips through the cervix ahead of the baby, getting compressed and cutting off oxygen), nuchal cord (cord wrapped around the baby’s neck), and true knots in the cord. While nuchal cords are common and often harmless, tight wrapping or knots can restrict oxygen flow.

Labor dystocia, or difficult labor, occurs when labor fails to progress despite adequate contractions. This can happen if the baby is too large for the pelvis, positioned awkwardly, or if contractions aren’t strong enough to dilate the cervix. Prolonged labor increases infection risk and can exhaust the laboring person, sometimes necessitating cesarean delivery.

Shoulder dystocia happens when the baby’s head delivers but the shoulders get stuck behind the pubic bone. This is an obstetric emergency requiring specific maneuvers to free the baby quickly before oxygen deprivation causes injury. Shoulder dystocia can result in nerve damage to the baby’s arm (brachial plexus injury) or fractures.

Post-Term Pregnancy Beyond 42 Weeks

Post-term pregnancy, also called prolonged pregnancy, refers to pregnancies lasting beyond 42 weeks. The placenta, which has been functioning throughout pregnancy, can begin to age and decline in efficiency, reducing oxygen and nutrient delivery to the baby.

Risks to the baby include:

• Macrosomia (growing very large, increasing delivery complications)
• Decreased amniotic fluid
• Meconium aspiration (breathing in stool passed in utero)
• Oxygen deprivation
• Stillbirth (risk increases after 42 weeks)

Due to these risks, most providers recommend induction of labor between 41 and 42 weeks rather than waiting for spontaneous labor. Monitoring increases in the final weeks, typically including non-stress tests and amniotic fluid checks to ensure the baby remains healthy.

Macrosomia and Delivering Large Babies

Macrosomia means a baby weighs more than 8 pounds, 13 ounces at birth, regardless of gestational age. Very large babies can experience difficult deliveries and birth injuries, and their size increases risks for the birthing parent as well.

Causes include gestational or pre-existing diabetes (the most common cause), maternal obesity, excessive weight gain during pregnancy, post-term pregnancy, previous delivery of a large baby, and being male (boys tend to be slightly larger). Sometimes large babies occur with no identifiable risk factors.

Complications associated with macrosomia include:

• Difficulty passing through the birth canal
• Shoulder dystocia and associated injuries
• Higher likelihood of cesarean delivery or assisted vaginal delivery with forceps or vacuum
• Increased maternal risk of postpartum hemorrhage and severe perineal tears
• Baby’s risk of low blood sugar, breathing problems, and childhood obesity

When macrosomia is suspected (usually through fundal height measurements and ultrasound, though ultrasound weight estimates can be off by a pound or more), providers discuss risks and delivery options with families. Some may recommend scheduled cesarean delivery if the baby is estimated to be very large, particularly in diabetic mothers.

Infections During Late Pregnancy

Several infections become particularly concerning during the third trimester because they can affect labor, delivery, and newborn health.

Chorioamnionitis is an infection of the amniotic fluid and membranes surrounding the baby, usually caused by bacteria ascending from the vagina. It typically occurs after membranes rupture (water breaks) but can occasionally develop with intact membranes. Symptoms include fever, rapid heart rate in mother and baby, uterine tenderness, and foul-smelling amniotic fluid. The infection requires antibiotic treatment and usually prompts delivery.

Group B Streptococcus (GBS) is a type of bacteria commonly found in the vagina or rectum of healthy people. While harmless to adults, it can cause serious infections in newborns if passed during delivery. All pregnant people are screened for GBS between 35 and 37 weeks. Those who test positive receive IV antibiotics during labor to protect the baby, dramatically reducing transmission risk.

Other infections like urinary tract infections, sexually transmitted infections, or viral illnesses like influenza or COVID-19 can complicate late pregnancy and should be treated promptly under medical guidance.

Serious Complications That Can Occur Throughout Any Stage of Pregnancy

Certain complications don’t fit neatly into one trimester because they can arise at any point during pregnancy or even postpartum. Awareness of these risks helps ensure early detection and treatment.

Blood Clots and Venous Thromboembolism During Pregnancy

Pregnancy increases the risk of developing blood clots, specifically deep vein thrombosis (DVT) and pulmonary embolism (PE). The risk remains elevated throughout pregnancy and into the postpartum period, actually peaking in the weeks after delivery.

Multiple factors contribute to this increased risk. Blood becomes more prone to clotting during pregnancy as a protective mechanism against excessive bleeding during delivery. Growing uterus compresses veins in the pelvis and legs, slowing blood return to the heart. Reduced mobility, especially late in pregnancy or after cesarean delivery, further increases risk.

Warning signs of DVT include pain, swelling, warmth, and redness in one leg (usually the calf or thigh). Pulmonary embolism symptoms include sudden shortness of breath, chest pain that worsens with deep breathing, rapid heart rate, coughing up blood, and feeling anxious or lightheaded.

People with previous blood clots, clotting disorders, obesity, prolonged bed rest, or who undergo cesarean delivery face higher risk. Some may receive preventive blood-thinning medications during pregnancy. Any symptoms suggestive of blood clots require immediate medical evaluation because PE can be fatal if untreated.

Maternal Mental Health Throughout Pregnancy and After Birth

Mental health challenges during pregnancy and postpartum are medical conditions, not signs of weakness or character flaws. Depression and anxiety can emerge at any point during pregnancy, not just after delivery.

Prenatal depression affects an estimated 10-15% of pregnant people. Symptoms include persistent sadness, loss of interest in activities, changes in sleep and appetite, difficulty concentrating, feelings of worthlessness or guilt, and thoughts of death or suicide. These symptoms go beyond normal pregnancy worries or mood swings and interfere with daily functioning.

Anxiety disorders during pregnancy can manifest as excessive worry about the baby’s health, fear of childbirth, panic attacks, or obsessive thoughts. Some people develop specific phobias or health anxiety during pregnancy.

Postpartum depression (PPD) is more widely recognized but often still goes untreated. It’s different from the “baby blues” (mild mood changes affecting up to 80% of new parents in the first two weeks after birth). PPD involves more severe symptoms lasting beyond two weeks, including difficulty bonding with the baby, withdrawal from loved ones, or thoughts of harming yourself or the baby.

Perinatal mood disorders require treatment. They don’t just go away on their own, and they can affect both parent and child. Treatment options include therapy, medication (many antidepressants and anti-anxiety medications are safe during pregnancy and breastfeeding), support groups, and sometimes more intensive interventions. Untreated mental health conditions can affect prenatal care attendance, maternal health behaviors, fetal development, and parent-child bonding.

If you’re experiencing symptoms of depression or anxiety, tell your healthcare provider. They should screen for mental health concerns at prenatal visits, but don’t wait for screening if you’re struggling.

Birth Defects and Congenital Anomalies Detected at Different Times

Congenital anomalies, commonly called birth defects, are structural or functional abnormalities present at birth. While the developmental errors causing most major birth defects occur during the first trimester when organs are forming, detection often happens later as ultrasound technology can better visualize developing structures.

First-trimester screening (around 11-14 weeks) combines ultrasound measurements (particularly nuchal translucency, the fluid space at the back of the baby’s neck) with maternal blood tests to assess risk for chromosomal conditions like Down syndrome (trisomy 21), trisomy 18, and trisomy 13. Abnormal results don’t confirm a diagnosis but indicate increased risk, prompting discussion of diagnostic testing options.

Second-trimester anatomy scans (typically 18-22 weeks) provide detailed examination of fetal structures, detecting heart defects, neural tube defects like spina bifida, kidney abnormalities, cleft lip and palate, and limb differences. Some conditions aren’t visible until later in pregnancy as organs grow larger and function becomes observable.

Diagnostic tests like chorionic villus sampling (CVS, performed 10-13 weeks) or amniocentesis (typically 15-20 weeks) can definitively diagnose chromosomal conditions and some genetic disorders by analyzing fetal cells. These are optional tests offered to those at increased risk or following abnormal screening results.

The emotional impact of learning about potential or confirmed birth defects is profound. Families may need time to process information, meet with specialists, understand prognosis and treatment options, and make decisions about continuing or terminating the pregnancy. Comprehensive counseling should address medical facts without pressure toward any particular decision, recognizing that families’ values, beliefs, and circumstances differ.

Many babies with birth defects can be treated successfully, some requiring surgery shortly after birth or ongoing medical care throughout life. Knowing about conditions before birth allows families to prepare emotionally, make informed decisions about delivery location (often facilities with specialized pediatric services), and have necessary medical teams ready at birth.

Understanding Your Risk and Getting the Care You Need

Knowledge of pregnancy complications shouldn’t increase anxiety but rather empower you to be an active participant in your prenatal care. Most complications are manageable, especially when caught early through regular monitoring and open communication with healthcare providers.

Certain factors increase risk for various complications, including pre-existing medical conditions, previous pregnancy complications, age under 17 or over 35, obesity or being underweight, smoking or substance use, inadequate prenatal care, and high levels of stress or lack of social support. Being aware of your personal risk factors helps both you and your provider stay vigilant for specific complications.

Trust your instincts. You know your body better than anyone. If something feels wrong, seek medical attention even if you’re not sure whether it’s serious. Healthcare providers would rather you call about a false alarm than miss a true emergency. Warning signs that always require immediate medical attention include vaginal bleeding, severe abdominal or pelvic pain, sudden severe headache, vision changes, fever, decreased fetal movement after 28 weeks, and fluid leaking from the vagina.

Regular prenatal care remains the single most effective tool for preventing and managing pregnancy complications. These visits allow monitoring of your health and the baby’s development, early detection of problems, evidence-based treatments when issues arise, education about warning signs, and support for both physical and mental health throughout pregnancy and beyond.