Sudden infant death syndrome (SIDS) is the sudden death of an infant that is unexplainable by the infant's history. The death also remains unexplainable upon autopsy. Infants exposed to smoke, both during pregnancy and after birth, are found to be more at risk of SIDS due to the increased levels of nicotine often found in SIDS cases. Infants exposed to smoke during pregnancy are up to three times more likely to die of SIDS that children born to non-smoking mothers.

Smoking during pregnancy can result in lower birth weight as well as deformities in the baby. Smoking nearly doubles the risk of low birthweight babies. In 2004, 11.9% of babies born to smokers had low birthweight as compared to only 7.2% of babies born to nonsmokers. More specifically, infants born to smokers weigh on average 200 grams less than infants born to women who do not smoke.

The nicotine in cigarette smoke constricts the blood vessels in placenta and carbon monoxide, which is poisonous, enters the baby's bloodstream, replacing some of the valuable oxygen molecules carried by hemoglobin in the red blood cells. Moreover, because the fetus cannot breathe the smoke out, he has to wait for the placenta to clear it. These effects account for the fact that, on average, babies born to smoking mothers are usually born too early and have low birth weight (less than 2,500 grams or 5.5 pounds), making it more likely the baby will become sick or die.

Premature and low birth weight babies face an increased risk of serious health problems as newborns have chronic lifelong disabilities such as cerebral palsy (a set of motor conditions causing physical disabilities), mental retardation and learning problems.

A number of studies have shown that tobacco use is a significant factor in miscarriages among pregnant smokers, and that it contributes to a number of other threats to the health of the fetus. Smoking and pregnancy, combined, cause twice the risk of premature rupture of membranes, placental abruption and placenta previa. Also, it causes 30% higher odds of the baby being born prematurely.

Cannabis in pregnancy is the subject of various scientific studies, usually regarding whether it has effects on the child later in life.

Effects found by Fergusson, D. M., Horwood, L. J., & Northstone, K. (2002) where that cannabis had a negative effect on babies. They were found to weigh significantly less, as well having shorter birth lengths, and had smaller head circumferences than babies who were not exposed to prenatal cannabis. Marijuana use has been shown to affect global motion perception by considerably increasing it, unlike alcohol that significantly decreases it.

Factors increasing the risk (to either the woman, the fetus/es, or both) of pregnancy complications beyond the normal level of risk may be present in a woman's medical profile either before she becomes pregnant or during the pregnancy. These pre-existing factors may relate to physical and/or mental health, and/or to social issues, or a combination.

Some common risk factors include:

- Age of either parent

- Adolescent parents

- Older parents

- Exposure to environmental toxins in pregnancy

- Exposure to recreational drugs in pregnancy:

- Ethanol during pregnancy can cause fetal alcohol syndrome and fetal alcohol spectrum disorder.

- Tobacco smoking and pregnancy, when combined, causes twice the risk of premature rupture of membranes, placental abruption and placenta previa. Also, it causes 30% higher odds of the baby being born prematurely.

- Prenatal cocaine exposure is associated with, for example, premature birth, birth defects and attention deficit disorder.

- Prenatal methamphetamine exposure can cause premature birth and congenital abnormalities. Other investigations have revealed short-term neonatal outcomes to include small deficits in infant neurobehavioral function and growth restriction when compared to control infants. Also, prenatal methamphetamine use is believed to have long-term effects in terms of brain development, which may last for many years.

- Cannabis in pregnancy is possibly associated with adverse effects on the child later in life.

- Exposure to Pharmaceutical drugs in pregnancy. Anti-depressants, for example, may increase risks of such outcomes as preterm delivery.

- Ionizing radiation

- Risks arising from previous pregnancies:

- Complications experienced during a previous pregnancy are more likely to recur.

- Many previous pregnancies. Women who have had five previous pregnancies face increased risks of very rapid labor and excessive bleeding after delivery.

- Multiple previous fetuses. Women who have had more than one fetus in a previous pregnancy face increased risk of mislocated placenta.

- Multiple pregnancy, that is, having more than one fetus in a single pregnancy.

- Social and socioeconomic factors. Generally speaking, unmarried women and those in lower socioeconomic groups experience an increased level of risk in pregnancy, due at least in part to lack of access to appropriate prenatal care.

- Unintended pregnancy. Unintended pregnancies preclude preconception care and delays prenatal care. They preclude other preventive care, may disrupt life plans and on average have worse health and psychological outcomes for the mother and, if birth occurs, the child.

- Height. Pregnancy in women whose height is less than 1.5 meters (5 feet) correlates with higher incidences of preterm birth and underweight babies. Also, these women are more likely to have a small pelvis, which can result in such complications during childbirth as shoulder dystocia.

- Weight

- Low weight: Women whose pre-pregnancy weight is less than 45.5 kilograms (100 pounds) are more likely to have underweight babies.

- Obese women are more likely to have very large babies, potentially increasing difficulties in childbirth. Obesity also increases the chances of developing gestational diabetes, high blood pressure, preeclampsia, experiencing postterm pregnancy and/or requiring a cesarean delivery.

- Intercurrent disease in pregnancy, that is, a disease and condition not necessarily directly caused by the pregnancy, such as diabetes mellitus in pregnancy, SLE in pregnancy or thyroid disease in pregnancy.

One out of 67 women who drink alcohol during pregnancy will have a child with a birth defect. The five countries with the highest prevalence of alcohol use during pregnancy were Ireland (about 60%), Belarus (47%), Denmark (46%), the UK (41%) and the Russian Federation (37%). The lowest prevalence is in those nations whose religious beliefs govern their alcohol consumption. Birth defects caused by alcohol consumption may be up to 1% in many places. This may mean that FASD may be higher than anencephaly, Down syndrome, spina bifida and trisomy 18. Globally, one in 10 women drink alcohol during pregnancy. Out of this population, 20% binge drink and have four or more alcoholic drinks per single occasion.

"Binge drinking is the direct cause of FAS or FASD. These findings are alarming because half of the pregnancies in developed countries and over 80% in developing countries are unplanned. That means that many women don’t realize they are pregnant during the early stages and that they continue drinking when pregnant."

Starting in 1981, the surgeon general of the United States started releasing a warning asking pregnant women to abstain from alcohol for the remainder of gestation.

Some disorders and conditions can mean that pregnancy is considered high-risk (about 6-8% of pregnancies in the USA) and in extreme cases may be contraindicated. High-risk pregnancies are the main focus of doctors specialising in maternal-fetal medicine.

Serious pre-existing disorders which can reduce a woman's physical ability to survive pregnancy include a range of congenital defects (that is, conditions with which the woman herself was born, for example, those of the heart or , some of which are listed above) and diseases acquired at any time during the woman's life.

Studies have found after controlling for other factors that some effects are present in pregnancies involving cocaine: abruptio placenta, prematurity, low birth weight, and small size compared to babies of the same gestational time. PCE newborns have smaller heads and shorter bodies. PCE effects are more severe when the amounts of cocaine are greater. As many as 17–27% of cocaine-using pregnant women deliver prematurely. In association with prematurity, growth in the womb is reduced, and low birth weight is connected to PCE. There are also data showing that spontaneous abortion is associated with cocaine use. Cocaine reduces the appetite and has been linked with reduced maternal weight gain during pregnancy; in addition, constriction of the blood vessels may further limit supply of nutrients to the fetus. Using cocaine while pregnant also heightens the chances of maternal and fetal vitamin deficiencies,

respiratory distress syndrome for the baby, and infarction of the bowels. Early reports found that cocaine-exposed babies were at high risk for sudden infant death syndrome; however, by itself, cocaine exposure during fetal development has not subsequently been identified as a risk factor for the syndrome. Some, but not all, PCE children experience hypertonia (excessive muscle tone), and reduced reflexes and motor function have been found in babies four to six weeks old.

While newborns who were exposed prenatally to drugs such as barbiturates or heroin frequently have symptoms of drug withdrawal (neonatal abstinence syndrome), this does not happen with babies exposed to crack "in utero"; at least, such symptoms are difficult to separate in the context of other factors such as prematurity or prenatal exposure to other drugs.

The risk of pregnancy complications increases as the mother's age increases. Risks associated with childbearing over the age of 50 include an increased incidence of gestational diabetes, hypertension, delivery by caesarean section, miscarriage, preeclampsia, and placenta previa. In comparison to mothers between 20 and 29 years of age, mothers over 50 are at almost three times the risk of low birth weight, premature birth, and extremely premature birth; their risk of extremely low birth weight, small size for gestational age, and fetal mortality was almost double.

A number of the effects that had been thought after early studies to be attributable to prenatal exposure to cocaine are actually due partially or wholly to other factors, such as exposure to other substances (including tobacco, alcohol, or marijuana) or to the environment in which the child is raised.

PCE is very difficult to study because of a variety of factors that may confound the results: pre- and postnatal care may be poor; the pregnant mother and child may be malnourished; the amount of cocaine a mother takes can vary; she may take a variety of drugs during pregnancy in addition to cocaine; measurements for detecting deficits may not be sensitive enough; and results that are found may only last a short time. Studies differ in how they define heavy or light cocaine use during pregnancy, and the time period of exposure during pregnancy on which they focus (e.g. first, second, or third trimester. Drug use by mothers puts children at high risk for exposure to toxic or otherwise dangerous environments, and PCE does not present much risk beyond these risk factors. PCE is clustered with other risk factors to the child, such as physical abuse and neglect, domestic violence, and prenatal exposure to other substances. Such environmental factors are known to adversely affect children in the same areas being studied with respect to PCE.

Most women who use cocaine while pregnant use other drugs too; one study found that 93% of those who use cocaine or opiates also use tobacco, marijuana, or alcohol. When researchers control for use of other drugs, many of the seeming effects of cocaine on head size, birth weight, Apgar scores, and prematurity disappear.

Addiction to any substance, including crack, may be a risk factor for child abuse or neglect. Crack addiction, like other addictions, distracts parents from the child and leads to inattentive parenting. Mothers who continue to use drugs once their babies are born have trouble forming the normal parental bonds, more often interacting with their babies with a detached, unenthusiastic, flat demeanor. Conversely, low-stress environments and responsive caregiving may provide a protective effect on the child's brain, potentially compensating for negative effects of PCE.

Many drug users do not get prenatal care, for a variety of reasons including that they may not know they are pregnant. Many crack addicts get no medical care at all and have extremely poor diets, and children who live around crack smoking are at risk of inhaling secondary smoke. Cocaine using mothers also have a higher rate of sexually transmitted infections such as HIV and hepatitis.

In some cases, it is not clear whether direct results of PCE lead to behavioral problems, or whether environmental factors are at fault. For example, children who have caregiver instability may have more behavioral problems as a result, or it may be that behavioral problems manifested by PCE children lead to greater turnover in caregivers. Other factors that make studying PCE difficult include unwillingness of mothers to tell the truth about drug history, uncertainty of dosages of street drugs and high rates of attrition (loss of participants) from studies.

Drug and alcohol use during pregnancy can lead to many health problems in the baby besides NAS. These may include:

- Birth defects

- Low birth weight

- Premature birth

- Small head circumference

- Sudden infant death syndrome (SIDS)

- Problems with development and behavior

Neonatal abstinence syndrome treatment can last from 1 week to 6 months. Even after medical treatment for NAS is over and babies leave the hospital, they may need continued treatment for weeks or months.

A 2012 study from the University of Michigan and the University of Pittsburgh published in the "Journal of the American Medical Association" analyzed information on 7.4 million discharges from 4,121 hospitals in 44 states, to measure trends and costs associated with NAS over the past decade. The study indicated that between 2000 and 2009, the number of mothers using opiates increased from 1.19 to 5.63 per 1,000 hospital births per year. Newborns with NAS were 19% more likely than all other hospital births to have low birthweight and 30% more like to have respiratory complications. Between 2000 and 2009, total hospital charges for NAS cases, adjusted for inflation, are estimated to have increased from $190 million to $720 million.

Neonatal abstinence syndrome in Canada are significant.

Facts about the conception of pregnancies in this age group can be difficult to determine, but they are nearly always due to the use of IVF with donor eggs.

DES (diethylstilbestrol) is a drug that mimics estrogen, a female hormone. From 1938 until 1971 doctors prescribed this drug to help some pregnant women who had had miscarriages or premature deliveries on the theory that miscarriages and premature births occurred because some pregnant women did not produce enough estrogen naturally to sustain the pregnancy for full term . An estimated 5-10 million pregnant women and the children born during this period were exposed to DES. Currently, DES is known to increase the risk of breast cancer, and cause a variety of birth-related adverse outcomes exposed female offsprings such as spontaneous abortion, second-trimester pregnancy loss, preterm delivery, stillbirth, neonatal death, sub/infertility and cancer of reproductive tissues . DES is an important developmental toxicant which links the fetal basis of adult disease.

Methylmercury and inorganic mercury is excreted in human breast milk and infants are particularly susceptible to toxicity due to this compound. The fetus and infant are especially vulnerable to mercury exposures with special interest in the development of the CNS since it can easily cross across the placental barrier, accumulate within the placenta and fetus as the fetus cannot eliminate mercury and have a negative effect on the fetus even if the mother does not show symptoms. Mercury causes damage to the nervous system resulting from prenatal or early postnatal exposure and is very likely to be permanent.

A number of studies have shown that tobacco use is a significant factor in miscarriages among pregnant smokers, and that it contributes to a number of other threats to the health of the fetus. It slightly increases the risk of neural tube defects.

Environmental tobacco smoke exposure and maternal smoking during pregnancy have been shown to cause lower infant birth weights.

Studies have shown an association between prenatal exposure to environmental tobacco smoke and conduct disorder in children. As well, post-natal tobacco smoke exposure may cause similar behavioral problems in children.

Women who smoke have about a 50% higher chance of giving birth to a child with behavioral disorders, such as ADHD, but a recent study in a book called "Attention Deficit Disorder: A Different Perception" overturns this, saying that ADHD is a genetic trait. Proof of this comes from a study showing that the people with ADHD had higher levels of certain hormones, as Thom Hartman explains with the hunter vs. farmer hypothesis.

In addition to increasing the risk of kidney cancer, smoking can also contribute to additional renal damage. Smokers are at a significantly increased risk for chronic kidney disease than non-smokers. A history of smoking encourages the progression of diabetic nephropathy.

Amount, frequency, and timing of prenatal alcohol use can dramatically impact the other three key features of FASD. While consensus exists that alcohol is a teratogen, there is no clear consensus as to what level of exposure is toxic. The CDC guidelines are silent on these elements diagnostically. The IOM and Canadian guidelines explore this further, acknowledging the importance of significant alcohol exposure from regular or heavy episodic alcohol consumption in determining, but offer no standard for diagnosis. Canadian guidelines discuss this lack of clarity and parenthetically point out that "heavy alcohol use" is defined by the National Institute on Alcohol Abuse and Alcoholism as five or more drinks per episode on five or more days during a 30-day period.

"The 4-Digit Diagnostic Code" ranking system distinguishes between levels of prenatal alcohol exposure as "high risk" and "some risk". It operationalizes high risk exposure as a blood alcohol concentration (BAC) greater than 100 mg/dL delivered at least weekly in early pregnancy. This BAC level is typically reached by a 55 kg female drinking six to eight beers in one sitting.

For many adopted or adults and children in foster care, records or other reliable sources may not be available for review. Reporting alcohol use during pregnancy can also be stigmatizing to birth mothers, especially if alcohol use is ongoing. In these cases, all diagnostic systems use an unknown prenatal alcohol exposure designation. A diagnosis of FAS is still possible with an unknown exposure level if other key features of FASD are present at clinical levels.

There are many causes of "fetal distress" including:

- Breathing problems

- 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

Instead of referring to "fetal distress" current recommendations hold to look for more specific signs and symptoms, assess them, and take the appropriate steps to remedy the situationthrough the implementation of intrauterine resuscitation. Traditionally the diagnosis of "fetal distress" led the obstetrician to recommend rapid delivery by instrumental delivery or by caesarean section if vaginal delivery is not advised.