Fetal Complications: Problems That Affect the Baby During Pregnancy

How fetal complications differ from maternal complications

Some problems start in the mother, such as preeclampsia or diabetes, and affect the baby through the placenta. Others start in the baby, such as a genetic condition or a heart defect. Placental problems sit in between. Doctors often manage both at once, because treating the mother is frequently the best way to protect the baby.

Main types of fetal complications

Fetal growth restriction

The baby is smaller than expected for the stage of pregnancy, usually defined as an estimated weight below the 10th percentile. The most common cause is a placenta that does not deliver enough oxygen and nutrients, often linked to high blood pressure, smoking or preeclampsia. Infections and chromosomal conditions are other causes. See intrauterine growth restriction.

Large baby (macrosomia)

A baby estimated to weigh more than about 4,000 to 4,500 g (8 lb 13 oz to 9 lb 15 oz). It is linked to diabetes in pregnancy, obesity and going past the due date, and raises the risk of a difficult birth.

Preterm birth

Birth before 37 weeks. Babies born very early (before 32 weeks) may have breathing, feeding, brain and eye problems. Signs of preterm labor include regular contractions, pelvic pressure, a low backache and fluid or blood from the vagina.

Birth defects

Structural or functional problems present at birth, affecting about 1 in 33 babies in the US. They include heart defects, cleft lip and palate, neural tube defects such as spina bifida, and chromosomal conditions such as Down syndrome. Many are found on the 18 to 22 week anatomy scan.

Infections passed to the baby

Some infections cross the placenta or pass to the baby at birth. They include cytomegalovirus, toxoplasmosis, rubella, syphilis, Zika, herpes, group B strep and listeria. These are sometimes grouped as TORCH infections.

Blood group incompatibility (Rh disease)

If the mother is Rh-negative and the baby is Rh-positive, the mother can make antibodies that destroy the baby's red blood cells, causing anemia and, in severe cases, heart failure in the baby. Rh disease is now rare because Rh-negative mothers receive anti-D immunoglobulin.

Amniotic fluid problems

• Too little fluid (oligohydramnios): linked to leaking membranes, placental problems and kidney or urinary problems in the baby.
• Too much fluid (polyhydramnios): linked to diabetes, twin problems and conditions that stop the baby swallowing normally.

Placental and cord problems

• Placental abruption: the placenta separates early, causing bleeding and pain and cutting the baby's oxygen supply.
• Placenta previa: the placenta covers the cervix, causing painless bleeding.
• Cord prolapse or compression: the cord slips ahead of the baby or is squeezed, lowering blood flow.

Fetal distress and stillbirth

"Fetal distress" is an older term, now usually called a non-reassuring fetal heart rate, meaning monitoring suggests the baby is not getting enough oxygen. Stillbirth is the loss of a baby at or after 20 weeks (24 weeks in the UK). Many stillbirths are linked to placental problems and growth restriction.

Risk factors

• High blood pressure, diabetes, kidney disease or autoimmune disease
• Smoking, alcohol and recreational drugs
• Age under 18 or over 35
• Twins or more
• A previous preterm birth, growth-restricted baby or stillbirth
• Certain medicines, such as some seizure drugs and isotretinoin
• Infections during pregnancy
• Not getting prenatal care

How fetal complications are found

• First-trimester screening: a blood test and nuchal translucency scan, or cell-free DNA testing, estimates the chance of chromosomal conditions.
• Anatomy scan at 18 to 22 weeks: checks the baby's organs, the placenta and fluid.
• Fundal height: the distance from pubic bone to top of the womb, measured from about 24 weeks. A small or large measurement prompts a growth scan.
• Growth scans and Doppler ultrasound: measure the baby's size and the blood flow in the umbilical cord and baby's vessels.
• Nonstress test and biophysical profile: monitor the baby's heart rate and movements later in pregnancy.
• Diagnostic tests: chorionic villus sampling or amniocentesis confirm genetic conditions.
• Blood tests in the mother: blood group and antibodies, infection screening and glucose testing.

Management

Management depends on the problem and how far along the pregnancy is. Options include:

• more frequent scans and heart rate monitoring
• treating the mother's condition, such as blood pressure control or insulin for gestational diabetes
• low-dose aspirin started early in pregnancy for people at high risk of preeclampsia, only on a doctor's advice
• steroid injections for the mother before an expected early birth, to mature the baby's lungs
• magnesium sulfate before very early births, to protect the baby's brain
• planning delivery at a hospital with a neonatal intensive care unit
• early delivery, by induction or cesarean, when the risks of staying in the womb outweigh the risks of being born early
• rarely, treatment in the womb, such as blood transfusions for severe anemia or surgery for some defects

Reducing the risk

• Start prenatal care early and attend all scheduled visits and scans.
• Take folic acid (400 micrograms a day) from before conception through the first 12 weeks.
• Do not smoke, drink alcohol or use drugs during pregnancy.
• Get recommended vaccines, including flu, Tdap and RSV at the right weeks.
• Avoid unpasteurized cheeses and undercooked meat, and wash hands after changing cat litter or handling raw meat.
• Learn your baby's pattern of movements and report any reduction promptly.

Frequently asked questions

What are the most common fetal complications?

The most common are preterm birth, fetal growth restriction and birth defects. Preterm birth affects about 1 in 10 US babies, and birth defects about 1 in 33. Infections, Rh disease and amniotic fluid problems are less common.

What are signs that something is wrong with the baby during pregnancy?

The most important sign is a reduction or change in the baby's movements after about 24 weeks. Vaginal bleeding, fluid leaking, regular contractions before 37 weeks, severe belly pain and a severe headache with vision changes also need prompt assessment.

Can fetal complications be prevented?

Not all of them, since many are genetic or unexplained. You can lower the risk by taking folic acid, avoiding smoking and alcohol, managing blood pressure and diabetes, getting vaccinated, attending scans, and reporting warning signs early so monitoring and treatment can start sooner.

Does a complication mean the baby will be born early?

Not always. Many complications are managed with closer monitoring until a normal due date. Doctors recommend early delivery only when tests show the baby would be safer outside the womb, and they usually give steroid injections first to help the baby's lungs.