What Are the Chances of Stillbirth by Week of Pregnancy?

The risk of stillbirth varies substantially across pregnancy, and the pattern is not a simple upward climb. At term, a large meta-analysis of 15 million pregnancies found the prospective risk of stillbirth rose from about 0.11 per 1,000 ongoing pregnancies at 37 weeks to 3.18 per 1,000 at 42 weeks, a roughly 30-fold increase over just five weeks.¹ But the story before term is different, shaped by causes like infection, placental problems, and fetal growth restriction rather than the simple passage of time. Understanding how these risks play out week by week helps explain why clinicians monitor pregnancies the way they do and why delivery timing matters so much.

How Risk Changes Week by Week at Term

Most conversations about stillbirth risk by gestational week focus on the term and post-term period, roughly 37 weeks onward, because this is where families and obstetricians face real decisions about when to deliver. The data here are strikingly clear. In the same meta-analysis of cohort studies covering 15 million pregnancies, researchers tracked what they call the “prospective” stillbirth risk: the chance that a baby still alive at the start of any given week will be stillborn before the next week begins. At 37 weeks that risk was about 0.11 per 1,000 ongoing pregnancies. By 39 weeks, the risk had begun a noticeable uptick, and by 41 weeks it climbed further. At 42 weeks the rate reached 3.18 per 1,000.¹

To put that in practical terms: the study found that continuing a pregnancy from 40 to 41 weeks increased the risk of stillbirth by about 64 percent compared to delivering at 40 weeks. One additional stillbirth occurred for roughly every 1,449 women who waited that extra week.¹ That 64 percent sounds alarming in relative terms, but the absolute numbers remain small; most pregnancies that continue to 41 weeks still end with a healthy baby. The sharp rise after 40 weeks is echoed across multiple reviews, with some describing it as beginning at 39 weeks and steepening noticeably after 40.²

Earlier in Pregnancy, Different Causes Dominate

The week-by-week risk curve at term tells only part of the story. In earlier pregnancy, stillbirth is less common per week but the causes are different. International reporting standards now classify stillbirths by gestational-age subgroups, with key thresholds at 22 weeks and 28 weeks, reflecting the reality that very early stillbirths and later ones often have distinct underlying pathology.³

Research on placental lesions in stillbirths at different gestational ages illustrates this well. Very early preterm stillbirths (before roughly 24 weeks) tend to involve obstetric complications and infections. In early preterm stillbirths (around 24 to 32 weeks), blood-flow problems from the mother to the placenta, known as uteroplacental insufficiency, become a leading factor. At term, umbilical cord problems and infection play larger roles.⁴ In other words, the risk at 24 weeks is driven by a different set of mechanisms than the risk at 40 weeks, even though both are captured under the single word “stillbirth.”

The Placenta and Why It Matters So Much

If there is one organ at the center of most stillbirth stories, it is the placenta. Across gestational ages, placental insufficiency, where the placenta fails to deliver enough blood, oxygen, or nutrients to the fetus, is the most common underlying mechanism linking growth restriction and fetal death. The pathological findings typically involve vascular abnormalities, though inflammatory lesions also appear.⁵

Researchers distinguish between maternal-side blood-flow problems (called maternal vascular malperfusion) and fetal-side problems (fetal vascular malperfusion). Maternal vascular malperfusion is the dominant finding in stillbirths linked to pre-eclampsia and growth restriction, especially when those conditions develop early. Fetal vascular malperfusion is strongly linked to stillbirth at term and to brain injury in newborns. Sometimes both are present, along with inflammatory damage.⁶ This is why, after a stillbirth, placental examination is the single most informative diagnostic step. Studies find it provides useful information in about 65 percent of cases, more than any other test including fetal autopsy.⁷

Fetal Growth Restriction Is the Strongest Individual Risk Factor

Among all identifiable risk factors for stillbirth, a baby that is not growing well in the womb stands out. A large population-based study found that fetal growth restriction roughly quadrupled the risk of stillbirth when it was detected before birth, and when it went undetected, the risk jumped eightfold.⁸ The overall stillbirth rate in that study was about 4.2 per 1,000 births, but among pregnancies with growth restriction the rate was nearly 17 per 1,000. When growth restriction was picked up on ultrasound and the pregnancy was monitored, the rate dropped to about 10 per 1,000. That gap between detected and undetected cases underscores why growth scans exist: catching a small baby early changes outcomes.

The detection of growth restriction through routine antenatal surveillance is one of the key goals of prenatal care, precisely because these babies face elevated stillbirth risk that can sometimes be managed with closer monitoring or earlier delivery.⁹

Maternal Health Conditions That Shift the Numbers

Your personal stillbirth risk at any given week is not just a function of gestational age. It is shaped by your health going into pregnancy. Chronic high blood pressure roughly doubles stillbirth risk compared to pregnancies without it. Women with chronic hypertension have an overall stillbirth rate of about 14 per 1,000 total births, compared to about 5 per 1,000 for women without it.¹⁰ The interaction with body weight is complex: in women without high blood pressure, higher BMI increases stillbirth risk at each gestational week in a straightforward gradient. But in women with chronic hypertension, that pattern partially reverses between 26 and 35 weeks, possibly because heavier women with hypertension are monitored and delivered earlier.

Gestational diabetes also elevates risk, with one study finding about 50 percent higher odds of stillbirth in mothers with gestational diabetes compared to those without it. Strikingly, the same study found that mothers who did not receive regular prenatal check-ups had nearly four times the odds of stillbirth, regardless of diabetes status.¹¹ The message is consistent across the literature: chronic conditions raise risk, but prenatal monitoring can offset a meaningful portion of that risk.

Umbilical Cord Problems

Cord abnormalities are one of the more frustrating causes of stillbirth because they are largely unpredictable with current technology. In a detailed cause-of-death analysis of nearly 500 stillbirths, about 19 percent were linked to umbilical cord abnormalities. Of those, roughly half involved compromised blood flow through the tiny vessels in the cord. Cord entrapment accounted for about 29 percent, and knots, torsion, or constriction made up another 27 percent.¹²

These problems can be either acquired, like a true knot that tightens during labor or a nuchal cord that wraps tightly around the neck, or congenital, like an abnormal insertion point where the cord attaches to the placenta. A velamentous cord insertion, where the cord’s blood vessels travel unprotected through the membranes before reaching the placenta, is a known risk factor.¹³ Cord-related stillbirths tend to cluster later in pregnancy, often at term, which partly explains the rising risk after 39 to 40 weeks.

Twin Pregnancies Have Their Own Timeline

If you are carrying twins, the week-by-week risk curve looks different from a singleton pregnancy, and the optimal delivery window comes earlier. For dichorionic twins (each baby with its own placenta), a meta-analysis found that the risk of stillbirth from continuing the pregnancy and the risk of neonatal death from delivering early reach a balance at about 37 weeks. Delaying delivery from 37 to 38 weeks was associated with an additional 8.8 perinatal deaths per 1,000 pregnancies.¹⁴

For monochorionic twins (sharing one placenta), the risk curve shifts even earlier, with a trend toward increasing stillbirths after 36 weeks. The numbers are smaller and the confidence intervals wider, but the pattern is consistent enough that clinical guidelines generally recommend delivering monochorionic twins by 36 to 37 weeks and dichorionic twins by 37 to 38 weeks. Separate data on U.S. twin pregnancies found that the composite risk of stillbirth and infant death rose significantly between 37 and 38 weeks, and that immediate delivery at 37 weeks was associated with lower mortality than waiting.¹⁵

Racial Disparities in Week-Specific Risk

In the United States, stillbirth risk is not distributed equally across racial groups, and the disparity is not constant across gestational age. Black women face about 2.2 times the overall stillbirth risk of white women, but the gap is widest in the earliest weeks. Between 20 and 23 weeks, Black women have about 2.75 times the stillbirth hazard of white women; by 39 to 40 weeks, the disparity narrows to about 1.57 times. Higher maternal education reduces the risk for white women more than for Black or Hispanic women, suggesting that the disparity is not simply explained by socioeconomic factors. Medical and pregnancy complications account for a larger share of stillbirth risk in Black women compared to white and Hispanic women.¹⁶

What About Fetal Movement Monitoring?

Many pregnant people are told to track their baby’s movements and to call their provider if those movements decrease. The evidence on this is more nuanced than you might expect. One large study found that women who reported decreased fetal movements and those who did not had the same overall stillbirth rate: about 0.1 percent.¹⁷ In other words, simply perceiving fewer movements did not reliably predict who was at risk.

However, other research draws a more specific distinction. In the Auckland Stillbirth Study, it was not the count of movements but the perceived strength that mattered: women who noticed their baby’s movements becoming weaker had more than twice the odds of late stillbirth.¹⁸ The practical takeaway is that “decreased fetal movement” is a broad category, and quality of movement may be more telling than quantity. Reporting changes remains sensible because it prompts evaluation, even if counting kicks on a chart is not a precise screening tool.

Delivery Timing for Low-Risk Pregnancies

The rising risk of stillbirth at term has prompted research into whether inducing labor at 39 weeks in low-risk women might prevent some deaths. A large randomized trial of first-time mothers without medical reasons for induction found that inducing between 39 and 39-and-a-half weeks was associated with a trend toward less perinatal harm, significantly fewer cesarean deliveries, and fewer blood-pressure complications compared to waiting for labor to start on its own.¹⁹ The trial was not specifically powered to detect a difference in stillbirth rates, which are too rare in low-risk populations for any single trial to settle the question definitively. But the overall pattern of reduced complications has influenced many clinicians to offer elective induction at 39 weeks, particularly for first pregnancies.

Recurrence Risk in a Subsequent Pregnancy

For parents who have experienced a stillbirth, the question of whether it could happen again in a future pregnancy is pressing. The answer is that the risk is elevated but still relatively low in absolute terms. One study comparing women with a first-pregnancy stillbirth to those with a first-pregnancy live birth found the stillbirth recurrence rate was about 2.5 percent, compared to 0.5 percent for women whose first pregnancy ended in a live birth, an adjusted hazard roughly twice as high.²⁰

The timing of the original stillbirth also matters. A population-based cohort study found that the highest recurrence risk was among women whose first stillbirth occurred early, between 22 and 28 weeks, though the confidence intervals were wide given the small numbers involved. After 32 weeks, the adjusted recurrence risk decreased.²¹ Clinicians typically manage subsequent pregnancies with more intensive surveillance, earlier growth scans, and in many cases earlier planned delivery, which likely helps keep the absolute recurrence rate as low as it is.

Extreme Temperatures and Stillbirth

An emerging area of research links environmental temperature extremes to stillbirth risk, particularly in the third trimester. A study of temperature exposure during pregnancy found that extreme heat, defined as the 97.5th percentile of local temperatures (about 30°C or 86°F in the study region), was associated with roughly 2.5 times the stillbirth risk compared to the optimal temperature of about 21°C, with the strongest effect in the final three months of pregnancy.²² A systematic review confirmed that both extreme cold (below about 15°C) and extreme heat (above roughly 23°C, with the highest risk above 29°C) were linked to increased stillbirth risk, with late pregnancy being the most vulnerable window.²³

The mechanisms are not fully worked out, but heat stress may reduce placental blood flow, while extreme cold triggers vasoconstriction that could have similar effects. These findings are particularly relevant as heat waves become more frequent. For pregnant people in their third trimester during summer months, staying cool is not just a comfort measure. Whether these temperature effects are large enough to show up at an individual level or primarily matter at a population level is still being debated, but the biological plausibility is strong given what we already know about placental blood flow and stillbirth.

Psychological Aftermath and Quality of Care

A systematic review of mental health outcomes after stillbirth found elevated rates of depression, anxiety, and post-traumatic stress that persisted well beyond the immediate aftermath, in both the short and long term, compared to parents who had live births.²⁴ Social support, marital status, and how care was handled after the loss all influenced symptom levels. The quality of care in the hospital turns out to matter a great deal. A cross-sectional study measuring adherence to stillbirth care guidelines found that when hospitals followed more than 40 of 60 recommended care practices, bereaved mothers reported substantially higher care satisfaction, greater experiences of respectful care, and markedly lower grief and PTSD symptoms.²⁵ These practices include things like offering to hold the baby, providing memory-making opportunities, clear communication about what happened, and follow-up counseling. The data suggest that the way a stillbirth is handled clinically is not a soft extra; it directly shapes long-term psychological recovery.

What a Stillbirth Workup Involves

When a stillbirth does occur, a thorough diagnostic workup is recommended, though families are often understandably unsure whether to consent. The evidence suggests that placental examination is the most consistently informative test, providing useful information in about 65 percent of cases. Fetal autopsy is useful in about 42 percent. Genetic testing and testing for antiphospholipid antibodies round out the most productive tests.²⁶ None of these tests alone identifies the cause in every case, and in a significant minority of stillbirths no definitive cause is ever found. But the workup matters for several reasons: it can identify conditions like blood-clotting disorders or chromosomal problems that would affect future pregnancies, and for many families it provides at least partial answers to questions that would otherwise go unanswered indefinitely.

Despite the established value of these tests, barriers to completion are common. Families may decline autopsy for personal or religious reasons, and some hospitals lack pathologists trained in perinatal pathology. A recent review highlighted that addressing these barriers, through better counseling about what each test involves and expanded access to specialized pathologists, could improve both the diagnostic yield and the support families receive during a devastating experience.⁷

1
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2
PubMed Central. Postterm pregnancy
3
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4
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5
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6
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7
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8
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9
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10
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11
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12
PubMed Central. Umbilical Cord Abnormalities and Stillbirth
13
PubMed Central. Prevention of stillbirths associated with umbilical cord abnormalities
14
BMJ. Prospective risk of stillbirth and neonatal complications in twin pregnancies: systematic review and meta-analysis
15
PubMed Central. The risk of stillbirth and infant death by each additional week of expectant management in twin pregnancies
16
PubMed Central. Racial Disparities in Stillbirth Risk Across Gestation in the United States
17
PubMed. Maternal perception of decreased fetal movements is independent of infant size
18
PubMed. Maternal perception of fetal activity and late stillbirth risk: findings from the Auckland Stillbirth Study
19
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20
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21
PubMed Central. Stillbirth and neonatal mortality in a subsequent pregnancy following stillbirth: a population-based cohort study
22
PubMed Central. Extreme temperature increases the risk of stillbirth in the third trimester of pregnancy
23
PubMed. Systematic review of ambient temperature exposure during pregnancy and stillbirth
24
PubMed Central. Depression, anxiety, PTSD, and OCD after stillbirth: a systematic review
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26
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