Stillbirth Causes: What Medical Science Actually Knows

The Question That Won't Stop

After a stillbirth, the need to know why is relentless. It surfaces at 3 a.m., mid-conversation, during an ultrasound with a subsequent pregnancy. And the hardest truth in perinatal medicine is that roughly 25% to 60% of stillbirths never receive a definitive cause — even with a full autopsy.

That does not mean the death was random or unpreventable. It means the diagnostic tools have limits. Here is what they can and cannot tell you.

Placental Conditions

Placental failure is the single largest identified cause of stillbirth, accounting for roughly one-third of cases where a cause is found. The placenta can fail in several ways:

Placental abruption occurs when the placenta separates from the uterine wall before delivery, cutting off blood and oxygen. Risk factors include hypertension, preeclampsia, and prior abruption. Symptoms sometimes include vaginal bleeding and severe abdominal pain, but a partial abruption can be clinically silent.

Placental insufficiency describes a placenta that cannot deliver adequate nutrients and oxygen, often detected through growth restriction on ultrasound. Histopathology frequently reveals infarction, chronic villitis, or maternal vascular malperfusion — all of which indicate the placenta was failing weeks before the death.

Umbilical cord complications — including true knots, cord compression, and thrombosis — account for roughly 10% of explained stillbirths. A cord finding on autopsy does not always prove it caused the death; pathologists look for tissue damage consistent with oxygen deprivation to confirm the connection.

Infections

Bacterial, viral, and parasitic infections cause an estimated 10% to 25% of stillbirths worldwide, with a higher proportion in low-resource settings. Common culprits include:

• Group B Streptococcus (GBS): Colonizes roughly 25% of pregnant women; routine 36-week screening exists, but earlier infection can reach the amniotic fluid before screening occurs
• Cytomegalovirus (CMV): The most common congenital infection; often asymptomatic in the mother
• Listeria monocytogenes: Contracted through contaminated food; causes placental inflammation and can lead to fetal death within days of maternal infection
• Parvovirus B19 (Fifth Disease): Attacks fetal red blood cells, causing severe anemia and hydrops fetalis
• Syphilis: Entirely preventable with early prenatal screening and treatment, yet still causes stillbirths when prenatal care is delayed or incomplete

Placental histopathology and maternal blood panels can often confirm or rule out infection, which is one reason pathologists strongly recommend examining the placenta even when families decline a full autopsy.

Chromosomal and Genetic Conditions

Chromosomal abnormalities — particularly trisomies 13, 18, and 21, as well as Turner syndrome (monosomy X) — are found in roughly 6% to 12% of stillbirths. The rate is higher among earlier losses.

Genetic microarray testing (such as chromosomal microarray analysis or karyotype) can detect these abnormalities from fetal tissue, cord blood, or placental samples. Microarray has a higher diagnostic yield than traditional karyotyping because it detects submicroscopic deletions and duplications that karyotyping misses.

One important timing detail: tissue samples for genetic testing should be collected before delivery whenever possible (via amniocentesis), because post-delivery samples have a higher culture failure rate — especially in macerated (decomposed) tissue.

Maternal Health Conditions

Several pre-existing or pregnancy-induced conditions carry elevated stillbirth risk:

• Preeclampsia and gestational hypertension: Disrupt blood flow to the placenta; preeclampsia can emerge suddenly, even in women with normal early-pregnancy blood pressure
• Diabetes (pre-existing and gestational): Poorly controlled blood glucose increases stillbirth risk 2 to 5 times; well-managed diabetes brings the risk closer to baseline
• Autoimmune conditions: Antiphospholipid syndrome is directly associated with recurrent pregnancy loss and stillbirth through placental blood clots
• Intrahepatic cholestasis of pregnancy (ICP): Characterized by severe itching in the third trimester; bile acid levels above 40 μmol/L carry a significantly elevated stillbirth risk

What Postmortem Testing Can Reveal

Families facing the autopsy decision deserve a clear picture of diagnostic yield. A full perinatal autopsy identifies or narrows the cause in over 40% of previously unexplained stillbirths. Placental histopathology alone provides useful findings in the majority of cases and does not involve any procedure on the baby's body.

Postmortem MRI is increasingly available as a non-invasive alternative — it excels at detecting central nervous system anomalies and is often more acceptable to families with religious or cultural objections to surgical autopsy.

The decision about testing is yours. But declining all investigation — particularly placental examination — means losing information that could change management in a future pregnancy.

What This Means for a Subsequent Pregnancy

If a cause is identified, your provider can build a targeted monitoring plan: additional ultrasounds for growth, early glucose screening, low-dose aspirin for preeclampsia prevention, or heparin therapy for clotting disorders. If no cause is found, enhanced fetal surveillance (typically starting at 28 to 32 weeks) and a discussion about timing of delivery are standard.

The Grief During Pregnancy guide walks through the autopsy decision framework, postmortem options (MRI, needle biopsy, and full autopsy), and how to use the findings to plan subsequent care — all in one place so you do not have to piece it together from hospital handouts at 2 a.m.

None of this makes the loss smaller. But knowing what happened, when that information is available, gives some parents a foothold in a landscape that otherwise feels entirely out of control.