Signs and symptoms
Generally it is preferable to describe specific signs in lieu of declaring fetal distress that include:

Decreased movement felt by the mother
Meconium in the amniotic fluid ("meconium stained fluid")
Non-reassuring patterns seen on cardiotocography:
increased or decreased fetal heart rate (tachycardia and bradycardia), especially during and after a contraction
decreased variability in the fetal heart rate
late decelerations
Biochemical signs, assessed by collecting a small sample of babys blood from a scalp prick through the open cervix in labor
fetal metabolic acidosis
elevated fetal blood lactate levels (from fetal scalp blood testing) indicating the baby has a lactic acidosisSome of these signs are more reliable predictors of fetal compromise than others. For example, cardiotocography can give high false positive rates, even when interpreted by highly experienced medical personnel. Metabolic acidosis is a more reliable predictor, but is not always available. Complications
Complications are primarily those associated with insufficient fetal oxygenation, most notably increased mortality risk. Other complications include fetal encephalopathy, seizures, cerebral palsy, and neurodevelopmental delay. Causes
Several conditions and risk factors can lead to fetal distress or non-reassuring fetal status, including:

Low amniotic fluid (oligohydramnios)
If there is too little amniotic fluid around the baby in the uterus, the baby can have trouble moving around in the uterus and its growth and temperature can be impacted. Low amniotic fluid can be caused by placental issues, high gestational blood pressure, some medications, as well as problems with the fetal kidney or urinary tract.
Meconium in the amniotic fluid
If a fetus has meconium in their lungs when they are born, this prevents the pressure in their lungs from falling, which normally facilitates the transition to independent breathing. Since aspiration of meconium can lead to improper oxygenation due to obstruction and carries the potential risk for inflammatory pneumonitis, this is an important diagnosis to make in the setting of newborn respiratory distress. Gestational Hypertension
If hypertension in the mother occurs after the 20th week and meets certain criteria, this is considered preeclampsia/eclampsia. The mechanism of preeclampsia/eclampsia is unknown, but consequences if left untreated can include fetal growth restriction or death, as well as pose medical risks to the mother. Signs and symptoms of preeclampsia can include swelling, protein in the urine, headaches, vomiting, and abnormal labs that assess kidney and liver function, some of which may be considered severe preeclampsia or eclampsia. Post-term pregnancy
Breathing problems
Anemia
Abnormal position and presentation of the fetus
Multiple births
Shoulder dystocia
Umbilical cord prolapse
Nuchal cord
Placental abruption
Premature closure of the fetal ductus arteriosus
Uterine rupture
Intrahepatic cholestasis of pregnancy, a liver disorder during pregnancy
Maternal diabetes (Type 1 or 2) or gestational diabetes (GDM)

Prevention
Monitoring of the mother and fetus prior to birth is critical to avoid complications after birth. This is often done via electronic fetal heart rate (FHR) monitoring, which helps providers monitor the fetus heart rate to ensure it is receiving enough oxygen, monitor the mothers contractions, and monitor the mothers blood pressure and systemic symptoms for gestational hypertension, preeclampsia, or eclampsia.