A number of factors have been identified that are linked to a higher risk of a preterm birth such as being less than 18 years of age. Maternal height and weight can play a role.

Further, in the US and the UK, black women have preterm birth rates of 15–18%, more than double than that of the white population. Filipinos are also at high risk of premature birth, and it is believed that nearly 11-15% of Filipinos born in the U.S. (compared to other Asians at 7.6% and whites at 7.8%) are premature. Filipinos being a big risk factor is evidenced with the Philippines being the 8th highest ranking in the world for preterm births, the only non-African country in the top 10. This discrepancy is not seen in comparison to other Asian groups or Hispanic immigrants and remains unexplained.

Pregnancy interval makes a difference as women with a six-month span or less between pregnancies have a two-fold increase in preterm birth. Studies on type of work and physical activity have given conflicting results, but it is opined that stressful conditions, hard labor, and long hours are probably linked to preterm birth.

A history of spontaneous (i.e., miscarriage) or surgical abortion has been associated with a small increase in the risk of preterm birth, with an increased risk with increased number of abortions, although it is unclear whether the increase is caused by the abortion or by confounding risk factors (e.g., socioeconomic status). Increased risk has not been shown in women who terminated their pregnancies medically. Pregnancies that are unwanted or unintended are also a risk factor for preterm birth.

Adequate maternal nutrition is important. Women with a low BMI are at increased risk for preterm birth. Further, women with poor nutrition status may also be deficient in vitamins and minerals. Adequate nutrition is critical for fetal development and a diet low in saturated fat and cholesterol may help reduce the risk of a preterm delivery. Obesity does not directly lead to preterm birth; however, it is associated with diabetes and hypertension which are risk factors by themselves. To some degree those individuals may have underlying conditions (i.e., uterine malformation, hypertension, diabetes) that persist.

Women with celiac disease have an increased risk of the development of preterm birth. The risk of preterm birth is more elevated when celiac disease remains undiagnosed and untreated.

Marital status is associated with risk for preterm birth. A study of 25,373 pregnancies in Finland revealed that unmarried mothers had more preterm deliveries than married mothers (P=0.001). Pregnancy outside of marriage was associated overall with a 20% increase in total adverse outcomes, even at a time when Finland provided free maternity care. A study in Quebec of 720,586 births from 1990 to 1997 revealed less risk of preterm birth for infants with legally married mothers compared with those with common-law wed or unwed parents.

Genetic make-up is a factor in the causality of preterm birth. Genetics has been a big factor into why Filipinos have a high risk of premature birth as the Filipinos have a large prevalence of mutations that help them be predisposed to premature births. An intra- and transgenerational increase in the risk of preterm delivery has been demonstrated. No single gene has been identified.

Subfertility is associated with preterm birth. Couples who have tried more than 1 year versus those who have tried less than 1 year before achieving a spontaneous conception have an adjusted odds ratio of 1.35 (95% confidence interval 1.22-1.50) of preterm birth. Pregnancies after IVF confers a greater risk of preterm birth than spontaneous conceptions after more than 1 year of trying, with an adjusted odds ratio of 1.55 (95% CI 1.30-1.85).

PROM occurring before 37 weeks (PPROM) is one of the leading causes of preterm birth. 30-35% of all preterm births are caused by PPROM. This puts the fetus at risk for the many complications associated with prematurity such as respiratory distress, brain bleeds, infection, necrotizing enterocolitis (death of the fetal bowels), brain injury, muscle dysfunction, and death. Prematurity from any cause leads to 75% of perinatal mortality and about 50% of all long-term morbidity. PROM is responsible for 20% of all fetal deaths between 24 and 34 weeks gestation.

The use of fertility medication that stimulates the ovary to release multiple eggs and of IVF with embryo transfer of multiple embryos has been implicated as an important factor in preterm birth. Maternal medical conditions increase the risk of preterm birth. Often labor has to be induced for medical reasons; such conditions include high blood pressure, pre-eclampsia, maternal diabetes, asthma, thyroid disease, and heart disease.

In a number of women anatomical issues prevent the baby from being carried to term. Some women have a weak or short cervix (the strongest predictor of premature birth) Women with vaginal bleeding during pregnancy are at higher risk for preterm birth. While bleeding in the third trimester may be a sign of placenta previa or placental abruption – conditions that occur frequently preterm – even earlier bleeding that is not caused by these conditions is linked to a higher preterm birth rate. Women with abnormal amounts of amniotic fluid, whether too much (polyhydramnios) or too little (oligohydramnios), are also at risk.

The mental status of the women is of significance. Anxiety and depression have been linked to preterm birth.

Finally, the use of tobacco, cocaine, and excessive alcohol during pregnancy increases the chance of preterm delivery. Tobacco is the most commonly abused drug during pregnancy and contributes significantly to low birth weight delivery. Babies with birth defects are at higher risk of being born preterm.

Passive smoking and/or smoking before the pregnancy influences the probability of a preterm birth. The World Health Organization published an international study in March 2014.

Presence of anti-thyroid antibodies is associated with an increased risk preterm birth with an odds ratio of 1.9 and 95% confidence interval of 1.1–3.5.

A 2004 systematic review of 30 studies on the association between intimate partner violence and birth outcomes concluded that preterm birth and other adverse outcomes, including death, are higher among abused pregnant women than among non-abused women.

The Nigerian cultural method of abdominal massage has been shown to result in 19% preterm birth among women in Nigeria, plus many other adverse outcomes for the mother and baby. This ought not be confused with massage conducted by a fully trained and licensed massage therapist or by significant others trained to provide massage during pregnancy, which has been shown to have numerous positive results during pregnancy, including the reduction of preterm birth, less depression, lower cortisol, and reduced anxiety.

The cause of premature rupture of membranes (PROM) is not clearly understood, but the following are risk factors that have been shown to increase the chance of it happening. In many cases, however, no risk factor is identified.

- Infections: urinary tract infection, sexually transmitted diseases, lower genital infections (ex: Bacterial Vaginosis), infections within the amniotic sac membranes

- Cigarette smoking during pregnancy

- Illicit drug use during pregnancy

- Having had PROM or preterm delivery in previous pregnancies

- Hydramnios: too much amniotic fluid

- Multiple gestation: being pregnant with two or more fetuses at one time

- Having had episodes of bleeding anytime during the pregnancy

- Invasive procedures (ex: amniocentesis)

- Nutritional deficits

- Cervical insufficiency: having a short or prematurely dilated cervix during pregnancy

- Low socioeconomic status

- Being underweight

There are several misfortunes associated with precipitate delivery for both the mother and the infant. They are classified as maternal and neonatal.

One reason that poverty produces such high rates of fistula cases is the malnutrition that exists in such areas. Lack of money and access to proper nutrition, as well as vulnerability to diseases that exist in impoverished areas because of limited basic health care and disease prevention methods, cause inhabitants of these regions to experience stunted growth. Sub-Saharan Africa is one such environment where the shortest women have on average lighter babies and more difficulties during birth when compared with full-grown women. This stunted growth causes expectant mothers to have skeletons unequipped for proper birth, such as an underdeveloped pelvis. This weak and underdeveloped bone structure increases the chances that the baby will get stuck in the pelvis during birth, cutting off circulation and leading to tissue necrosis. Because of the correlation between malnutrition, stunted growth, and birthing difficulties, maternal height can at times be used as a measure for expected labor difficulties.

High levels of poverty also lead to low levels of education among impoverished women concerning maternal health. This lack of information in combination with obstacles preventing rural women to easily travel to and from hospitals lead many to arrive at the birthing process without prenatal care. This can cause a development of unplanned complications that may arise during home births, in which traditional techniques are used. These techniques often fail in the event of unplanned emergencies, leading women to go to hospital for care too late, desperately ill, and therefore vulnerable to the risks of anesthesia and surgery that must be used on them. In a study of women who had prenatal care and those who had unbooked emergency births, “the death rate in the booked-healthy group was as good as that in many developed countries, [but] the death rate in the unbooked emergencies was the same as the death rate in England in the 16th and 17th centuries.” In this study, 62 unbooked emergency women were diagnosed with obstetric fistulae out of 7,707 studied, in comparison to three diagnosed booked mothers out of 15,020 studied. In addition, studies find that education is associated with lower desired family size, greater use of contraceptives, and increased use of professional medical services. Educated families are also more likely to be able to afford health care, especially maternal healthcare.

Emergency exploratory laparotomy with cesarean delivery accompanied by fluid and blood transfusion are indicated for the management of uterine rupture. Depending on the nature of the rupture and the condition of the patient, the uterus may be either repaired or removed (cesarean hysterectomy). Delay in management places both mother and child at significant risk.

During labor the shoulder will be wedged into the pelvis and the head lie in one iliac fossa, the breech in the other. With further uterine contractions the baby suffocates. The uterus continues to try to expel the impacted fetus and as its retraction ring rises, the musculature in the lower segments thins out leading eventually to a uterine rupture and the death of the mother. Impacted shoulder presentations contribute to maternal mortality. Obviously a cesarean section should be performed before the baby has died, but even when the baby has died or impaction has occurred, C/S is the method of choice of delivery, as alternative methods of delivery are potentially too traumatic for the mother. If the baby is preterm or macerated and very small a spontaneous delivery has been observed.

Fetal malformations and birth injuries may occur as a result of exposure to environmental toxins such as mercury or lead. Many medications can also affect the development of the fetus, as can alcohol, tobacco, and illicit drugs.

"See Environmental toxins and fetal development."

"See Drugs in pregnancy."

The most common cause is the mismanagement of 3rd stage of labor, such as:

- Fundal pressure

- Excess cord traction during the 3rd stage of labor

Other natural causes can be:

- Uterine weakness, congenital or not

- Precipitate delivery

- Short umbilical cord

It is more common in multiple gestation than in singleton pregnancies.

The incidence is of 1/2000 pregnancies.

A uterine scar from a previous cesarean section is the most common risk factor. (In one review, 52% had previous cesarean scars.) Other forms of uterine surgery that result in full-thickness incisions (such as a myomectomy), dysfunctional labor, labor augmentation by oxytocin or prostaglandins, and high parity may also set the stage for uterine rupture. In 2006, an extremely rare case of uterine rupture in a first pregnancy with no risk factors was reported.

Maternal infection may be transmitted to the fetus; this is called a vertically transmitted infection. The fetus has a weak immune system, so infections that are relatively minor in adults can be very serious in a developing fetus. In addition, some studies suggest that maternal infections increase the risk of neurodevelopmental disorders, including schizophrenia, in the child.

Precipitate delivery may cause lacerations of the cervix, vagina, and/or perineum. Rapid descent and delivery of an infant does not allow maternal tissues adequate time to stretch and accommodate the passage of the infant.

There may be hemorrhaging originating from lacerations and/or hematomas of the cervix, vagina, or perineum. There may also be hemorrhaging from the uterus. Uterine atony may result from muscular exhaustion after unusually strong and rapid labor.

There may be infection as a result of unsterile delivery.

Uterine inversion is often associated with significant Post-partum hemorrhage. Traditionally it was thought that it presented with haemodynamic shock "out of proportion" with blood loss, however blood loss has often been underestimated. The parasympathetic effect of traction on the uterine ligaments may cause bradycardia.

A woman who has reached 42 weeks of pregnancy is likely to be offered induction of labour. Alternatively, she can choose expectant management, that is, she waits for the natural onset of labour. Women opting for expectant management may also choose to carry on with additional monitoring of their baby, with regular CTG, ultrasound, and biophysical profile. Risks of expectant management vary between studies.

The delivery of the second twin in a transverse lie with a shoulder presentation represents a special situation that may be amenable to a vaginal delivery. As the first twin has just been delivered and the cervix is fully dilated the obstetrician may perform an internal version, that is inserting one hand into the uterus, find the baby’s feet, and then bring the baby into a breech position and deliver the baby as such.

Inducing labor artificially starts the labor process by using medication and other techniques. Labor is usually only induced if there is potential danger on the mother or child.

There are several reasons for labor induction; the mother's water breaks, and contractions have not started, the child is post-mature, the mother has diabetes or high blood pressure, or there is not enough amniotic fluid around the baby. Labor induction is not always the best choice because it has its own risks. Sometimes mothers will request to be induced for reasons that are not medical. This is called an elective induction. Doctors try to avoid inducing labor unless it is completely necessary.

Many factors can contribute to the loss of uterine muscle tone, including:

- overdistention of the uterus

- multiple gestations

- polyhydramnios

- fetal macrosomia

- prolonged labor

- oxytocin augmentation of labor

- grand multiparity (having given birth 5 or more times)

- precipitous labor (labor lasting less than 3 hours)

- magnesium sulfate treatment of preeclampsia

- chorioamnionitis

- halogenated anesthetics

- uterine leiomyomata

- full bladder

- retained colyledon, placental fragments

- placenta previa

- placental abruption

- constriction ring

- incomplete separation of the placenta

The primary concern with umbilical cord prolapse is inadequate blood supply, and thus oxygen, to the fetus if the cord becomes compressed. The cord can become compressed either due to mechanical pressure (usually from the presenting fetal part) or from sudden contraction of the vessels due to decreased temperatures in the vagina in comparison to the uterus. This can lead to death of the fetus or other complications.

Historically, the rate of fetal death in the setting of cord prolapse has been as high 40%. However, these estimates occurred in the context of home or births outside of the hospital. When considering cord prolapses that have occurred in inpatient labor and delivery settings, the rate drops to as low as 0-3%, though the mortality rate remains higher than for fetuses without cord prolapse. The reduction in mortality for hospital births is likely due to the ready availability of immediate cesarean section.

Many other fetal outcomes have been studied, including Apgar score (a quick assessment of a newborn's health status) at 5 minutes and length of hospitalization after delivery. While both measures are worse for newborns delivered after cord prolapse, it is unclear what effect this has in the long-term. Relatively large studies that have tried to quantify long-term effects of cord prolapse on children found that less than 1% (1 in 120 studied) suffered a major neurologic handicap, and less than 1% (110 in 16,675) had diagnosed cerebral palsy.

Risk factors that are associated with umbilical cord prolapse tend to make it difficult for the fetus from appropriately engaging and filling the maternal pelvis or are related to abnormalities of the umbilical cord. The two major categories of risk factors are spontaneous and iatrogenic, or those that result from medical intervention.

- spontaneous factors:

- fetal malpresentation: abnormal fetal lie tends to result in space below the fetus in the maternal pelvis, which can then be occupied by the cord.

- polyhydramnios, or an abnormally high amount of amniotic fluid

- prematurity: likely related to increased chance of malpresentation and relative polyhydramnios.

- low birth weight: usually described as <2500 g at birth, though some studies will use <1500g. Cause is likely similar to those for prematurity.

- multiple gestation, or being pregnant with more than one fetus at a given time: more likely to occur in the fetus that is not born first.

- spontaneous rupture of membranes: about half of prolapses occur within 5 minutes of membrane rupture, two-thirds within 1 hour, 95% within 24 hours.

- iatrogenic factors

- artificial rupture of membranes

- placement of internal monitors (for example, internal scalp electrode or intrauterine pressure catheter)

- manual rotation of fetal head

An obstetric labor complication is a difficulty or abnormality that arises during the process of labor or delivery.

An example is dystocia.

Chorioamnionitis is a risk factor for periventricular leukomalacia and cerebral palsy.

Physicians, Nurse Practitioners, Physician Assistants, Nurses and Midwives will typically ask for the need of relief. Women in labor have many pain relief options that work well and pose small risks when given by a trained and experienced clinician. Clinicians also can use different methods for pain relief at different stages of labor. Still, not all options are available at every hospital and birthing center. Depending on the health history of the mother, the presence of allergies or other concerns, some choices will work better than others.

There are many methods of relieving pain used for labor. Rare and unpredictable, serious complications sometimes occur. Also, most medicines used to manage pain during labor pass freely into the placenta to the baby. Asking questions about the procedures and medications might affect the baby are valid questions.

More and more women in the United States are using water to find comfort during labor. This is called hydrotherapy. Laboring in a tub of warm water helps women feel physically supported, and keeps them warm and relaxed. Plus, it is easier for laboring women to move and find comfortable positions in the water.

In waterbirthing, a woman remains in the water for delivery. The American Academy of Pediatrics has expressed concerns about delivering in water because of a lack of studies showing its safety and because of the rare but reported chance of complications. Ask your doctor or midwife if you want to know more about waterbirthing.