Stillbirth, the loss of a pregnancy after 20 weeks of gestation, affects about 1 in 175 births in the United States, resulting in roughly 21,000 cases each year. The causes range from problems with the placenta and umbilical cord to infections, genetic conditions, and maternal health issues. In many cases, multiple factors overlap, and even after thorough investigation, 16% to 36% of stillbirths have no identifiable explanation.
Placental Problems Are the Leading Cause
The placenta is the organ that delivers oxygen and nutrients from your bloodstream to the fetus. When it fails to work properly, a condition called placental insufficiency, the fetus can be deprived of what it needs to survive. This can happen gradually, leading to restricted fetal growth over weeks, or suddenly, as in a placental abruption where the placenta separates from the uterine wall before delivery.
At the tissue level, a failing placenta often shows infarctions (areas where blood flow has been cut off), blood clots, and excessive buildup of a protein called fibrin that blocks normal exchange between mother and fetus. These changes can be triggered by problems with blood vessel development early in pregnancy, immune system dysfunction, or chronic inflammation. Placental insufficiency is also the mechanism through which conditions like preeclampsia cause stillbirth, since high blood pressure damages the small vessels that feed the placenta.
Umbilical Cord Accidents
About 19% of stillbirths involve an umbilical cord abnormality. In a study of 496 stillbirths that underwent detailed cause-of-death analysis, 94 were linked to cord problems. The most common findings were compromised blood flow through the cord’s tiny vessels (48% of cord-related cases), the cord wrapping tightly around the neck or body with evidence of obstruction (29%), and true knots, twisting, or narrowing of the cord (27%). Cord prolapse, where the cord slips ahead of the baby and gets compressed, accounted for 5% of cord-related stillbirths.
What makes cord accidents particularly difficult is that many of them are unpredictable. A loose loop of cord around a baby’s neck is extremely common and almost always harmless. It only becomes dangerous when it tightens enough to cut off blood flow, something that can happen without warning.
Genetic and Structural Abnormalities
Fetal anomalies account for roughly 11% to 14% of stillbirths in U.S. data. When researchers examine stillborn babies more closely, about 23% have one or more major structural abnormalities, compared to just 4.3% of babies born alive. These can include chromosomal conditions where the fetus has extra or missing genetic material, as well as major defects in the heart, brain, kidneys, or other organs that are incompatible with survival.
Some of these conditions are inherited, but many arise from random errors during cell division early in pregnancy. They are not caused by anything the parents did or didn’t do. Genetic testing after a stillbirth can sometimes identify a specific cause, which may be important for understanding recurrence risk in future pregnancies.
Maternal Health Conditions
Certain health problems in the pregnant person significantly raise the risk. High blood pressure nearly doubles the odds of stillbirth compared to pregnancies without it. Gestational diabetes also increases risk, particularly when it goes undetected and unmanaged. In one large study, women with gestational diabetes who never received screening had nearly four times the odds of stillbirth compared to women without diabetes. However, women whose blood sugar was identified and managed through dietary changes alone showed no significant increase in risk, highlighting how much early detection matters.
Being over 35 also raises risk, with one study finding odds roughly 1.8 times higher than for younger mothers. A previous stillbirth is the strongest individual predictor: women who have experienced one stillbirth have nearly 10 times the odds of another in a subsequent pregnancy, though the absolute risk still remains relatively low.
Infections During Pregnancy
Infections cause stillbirth through two main routes. Some bacteria travel upward from the vagina into the uterus, causing inflammation of the membranes surrounding the fetus. Common culprits in this category include E. coli and Group B Streptococcus (GBS). Other infections reach the fetus by crossing the placenta through the mother’s bloodstream. Syphilis, listeriosis (often contracted from contaminated food), and toxoplasmosis (linked to undercooked meat or cat feces) all work this way.
Viral infections can also be responsible. Parvovirus B19 (sometimes called “fifth disease” in children) can cause severe anemia in the fetus. Cytomegalovirus (CMV), a common virus that causes mild or no symptoms in adults, can be devastating to a developing fetus. Chickenpox, rubella, and in some regions, malaria and dengue are additional risks. Many of these infections produce only mild symptoms in the mother, making them easy to miss without specific testing.
Racial and Socioeconomic Disparities
Stillbirth does not affect all communities equally. Black women in the United States face 2.2 times the risk of stillbirth compared to white women, a disparity that persists across all stages of pregnancy. The gap is widest in the earlier weeks (20 to 23 weeks), where Black women face nearly three times the risk, and narrows somewhat closer to full term, though it never disappears.
Education level, often used as a proxy for socioeconomic status, reduces risk for white women by about 30% when they have more than 12 years of education. For Black women, the protective effect of higher education is far smaller, cutting risk by only about 9%. This suggests that the disparity is not simply explained by income or access to care. Medical and pregnancy complications contribute to about 30% of the stillbirth risk among Black women compared to about 20% among white and Hispanic women, pointing to differences in underlying health conditions, quality of care, and the cumulative effects of systemic racism on health.
Why So Many Cases Remain Unexplained
Even with autopsy, placental examination, and genetic testing, somewhere between 16% and 60% of stillbirths have no identifiable cause. The wide range in that estimate reflects differences in how thoroughly cases are investigated and how “unexplained” is defined. When a comprehensive protocol is followed, including detailed placental pathology, chromosomal analysis, and infection screening, the unexplained rate typically falls to the 16% to 36% range.
This is one of the most frustrating realities for families. A stillbirth with no clear cause offers no roadmap for prevention in a future pregnancy and no answer to the question of why it happened. It also reflects genuine gaps in medical understanding of fetal development and the complex interactions between placenta, cord, genetics, and environment.
Monitoring Fetal Movement
One of the few things you can do at home to monitor fetal wellbeing is pay attention to your baby’s movement patterns. A noticeable decrease or absence of movement can be an early sign that something is wrong. If you feel your baby is moving less than usual, contact your maternity care provider immediately. Do not wait until the next day, and do not try strategies like drinking ice water or eating something and waiting to see what happens.
Your own perception of reduced movement matters more than any specific counting formula. Clinical guidelines emphasize that a mother’s concern overrides any numerical threshold. When you present to the hospital, the first step is confirming the baby’s heartbeat, followed by continuous heart rate monitoring, typically within two hours. If concerns persist despite normal initial readings, an ultrasound to check fluid levels and fetal size may be recommended within 24 hours. Repeat presentations for reduced movement, suspected growth restriction, or other risk factors for stillbirth all warrant closer investigation.