Stillbirth at 38 weeks is rare, but it does happen, and it’s one of the most devastating experiences a family can face. In the United States, more than 1 in 150 pregnancies end in stillbirth, and losses this late in pregnancy are often caused by problems with the placenta, the umbilical cord, or undetected restrictions in fetal growth. What makes 38-week losses particularly painful is that nearly 1 in 4 occur with no identifiable risk factor at all, according to research from Harvard’s T.H. Chan School of Public Health.
Understanding the causes won’t undo a loss, but for parents searching for answers or pregnant people looking to protect themselves, knowing what can go wrong and what signs to watch for is genuinely useful.
Placental Problems Are the Most Common Cause
The placenta is the organ that delivers oxygen and nutrients from mother to baby throughout pregnancy. When it stops working properly, a condition called placental insufficiency, the baby can be slowly starved of what it needs to survive. This can happen because the placenta didn’t grow large enough, has an irregular shape, or isn’t attached well to the uterine wall. In the most dangerous scenario, the placenta partially or fully separates from the uterine lining before birth (placental abruption), which can cut off the baby’s blood supply rapidly.
At 38 weeks, the baby is larger and more metabolically demanding than at any earlier point in pregnancy. A placenta that was functioning adequately at 34 or 36 weeks may no longer keep up. The result is fetal hypoxia, a lack of oxygen reaching the baby’s brain and organs. If the oxygen deprivation is severe or prolonged enough, it can cause death before anyone realizes something is wrong. This is one reason some providers recommend closer monitoring or induction for pregnancies with known placental concerns as they approach full term.
Umbilical Cord Accidents
The umbilical cord is the baby’s lifeline, and problems with it account for roughly 10 to 15 percent of all stillbirths. Cord accidents include true knots that tighten during movement, the cord wrapping around the baby’s neck or body, compression between the baby and the uterine wall, and abnormal cord insertion into the placenta.
Cords that are unusually long (over 80 cm), unusually short (under 35 cm), or excessively twisted are more vulnerable to these events. A baby at 38 weeks has less room to move than earlier in pregnancy, which can increase the risk of cord compression. Animal studies consistently show that even partial compression of the umbilical cord can lead to dangerous drops in oxygen and blood flow. The challenge is that cord accidents are nearly impossible to predict or detect on routine monitoring. They often happen suddenly, which is part of why they’re so devastating.
Undetected Growth Restriction
Fetal growth restriction, where a baby is significantly smaller than expected for its gestational age, is one of the strongest risk factors for stillbirth. Research published in PLOS Medicine found that abnormal fetal growth could be identified in about 25 percent of stillbirths using standard growth charts, but that number jumped to roughly 50 percent when more precise methods like ultrasound-based measurements were used. That gap matters: it means a significant number of growth-restricted babies are being missed by routine screening.
Babies whose weight falls below the 5th percentile for their gestational age face the highest risk. Growth restriction often signals that the placenta isn’t delivering enough nutrition, so it overlaps with placental insufficiency. The problem at 38 weeks is that many pregnancies aren’t getting detailed growth scans this late unless there’s already a known concern. A baby that appeared to be growing normally at a 34-week appointment may have fallen behind in the final weeks without anyone catching it. This is one of the most preventable categories of stillbirth, because identifying a growth-restricted baby allows providers to deliver earlier, before the situation becomes fatal.
Preeclampsia and Blood Pressure Disorders
Preeclampsia, a pregnancy complication involving dangerously high blood pressure and organ damage, is a well-established cause of stillbirth. It can reduce blood flow to the placenta, depriving the baby of oxygen. Preeclampsia sometimes develops suddenly in the final weeks of pregnancy, even in women who had normal blood pressure readings throughout. When it escalates quickly, it can cause placental abruption, seizures, or organ failure in the mother, all of which put the baby at immediate risk.
This is why blood pressure checks remain a routine part of every prenatal visit right up until delivery. Symptoms like sudden severe headaches, vision changes, upper abdominal pain, and rapid swelling in the face or hands can signal preeclampsia and warrant immediate evaluation.
Infections That Reach the Baby
Infections are more commonly linked to earlier pregnancy losses, but certain pathogens can cause stillbirth at any gestational age. Group B streptococcus, E. coli, listeria, cytomegalovirus, and parvovirus have all been identified in stillbirth cases. Listeria is particularly relevant for late-term losses because it can cross the placenta and infect the baby directly. It’s contracted through contaminated food, particularly soft cheeses, deli meats, and unpasteurized products.
Infections can trigger inflammation in the placenta and membranes surrounding the baby, disrupting the oxygen and nutrient supply. Some infections cause the baby to become septic. Because the symptoms in the mother can be mild or resemble a common flu, these infections sometimes go unrecognized until it’s too late.
Genetic and Structural Abnormalities
Some stillbirths at 38 weeks are caused by chromosomal abnormalities or structural problems with the baby’s heart or other organs that weren’t detected during pregnancy. Not all genetic conditions are picked up by standard prenatal screening, and some structural defects only become fatal as the baby grows larger and the demands on its body increase. These causes are less common at 38 weeks than earlier in pregnancy, but they do account for a portion of late losses, particularly when postmortem examination reveals conditions that weren’t visible on ultrasound.
Why Many Cases Have No Clear Explanation
Perhaps the hardest reality for families is that a significant number of 38-week stillbirths remain unexplained even after thorough investigation. The Harvard study found that 24.1 percent of stillbirths at 38 weeks had no identifiable risk factor. That doesn’t necessarily mean nothing went wrong. It means the cause wasn’t detectable with current diagnostic tools. Subtle placental dysfunction, brief cord compression events, or transient cardiac rhythm problems in the baby may leave no trace by the time the loss is discovered.
This is an area where medicine still has real limitations, and it’s important for grieving parents to understand that an unexplained stillbirth is not a reflection of something they did or failed to do.
The Warning Sign That Matters Most
Reduced fetal movement is the most important signal a pregnant person can monitor in the final weeks. Research from the Royal College of Obstetricians and Gynaecologists found that 55 percent of women who experienced a stillbirth noticed a reduction in their baby’s movements beforehand. Multiple studies in the UK and Norway have also found that when clinicians responded inadequately to reports of reduced movement, it was a common contributing factor in stillbirth.
The standard guidance is straightforward: if you don’t feel at least 10 distinct movements in a 2-hour window, contact your maternity provider immediately. Don’t wait until the next day. Don’t assume the baby is just sleeping. About 70 percent of women who report reduced movement will turn out to have a perfectly healthy pregnancy, so a false alarm is far better than a missed one. Providers will typically monitor the baby’s heart rate and, if needed, perform an ultrasound to check on growth and fluid levels.
Paying attention to your baby’s normal pattern of movement is more useful than counting to a specific number. You know what’s typical for your baby. A noticeable change from that pattern, especially a sustained quiet period, is worth reporting every single time.