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.

Not only is obesity associated with miscarriage, it can result in sub-fertility and other adverse pregnancy outcomes. Recurrent miscarriage is also related to obesity. Women with bulimia nervosa and anorexia nervosa may have a greater risk for miscarriage. Nutrient deficiencies have not been found to impact miscarriage rates but hyperemesis gravidarum sometimes precedes a miscarriage.

Caffeine consumption also has been correlated to miscarriage rates, at least at higher levels of intake. However, such higher rates have been found to be statistically significant only in certain circumstances.

Vitamin supplementation has generally not shown to be effective in preventing miscarriage. Chinese traditional medicine has not been found to prevent miscarriage.

The age of the pregnant woman is a significant risk factor. Miscarriage rates increase steadily with age, with more substantial increases after age 35. In those under the age of 35 the risk is about 10% while it is about 45% in those over the age of 40. Risk begins to increase around the age of 30. Paternal age is associated with increased risk.

Research shows that symptoms of Posttraumatic stress disorder are common following childbirth, with prevalence of 24-30.1% at 6 weeks, dropping to 13.6% at 6 months. PTSD is rarer; a review found that following normal childbirth (excluding stillbirth and some other complications) rates of PTSD ranged from 2.8-5.6% after 6 weeks, dropping to 1.5% at 6 months.

Immunization of mothers against male-specific minor histocompatibility (H-Y) antigens has a pathogenic role in many cases of "secondary recurrent miscarriage", that is, recurrent miscarriage in pregnancies succeeding a previous live birth. An example of this effect is that the male:female ratio of children born prior and subsequent to secondary recurrent miscarriage is 1.49 and 0.76 respectively.

Recurrent miscarriage in itself is associated with later development of coronary artery disease with an odds ratio of approximately 2, increased risk of ovarian cancer, increased risk of cardiovascular complications, and an increased risk of all-cause mortality of 44%, 86%, and 150% for women with a history of 1, 2, or 3 miscarriages, respectively.

Women with a history of recurrent miscarriage are at risk of developing preeclampsia in later pregnancies.

A pregnant woman may have intercurrent diseases, defined as disease not directly caused by the pregnancy, but that may become worse or be a potential risk to the pregnancy.

- Diabetes mellitus and pregnancy deals with the interactions of diabetes mellitus (not restricted to gestational diabetes) and pregnancy. Risks for the child include miscarriage, growth restriction, growth acceleration, fetal obesity (macrosomia), polyhydramnios (too much amniotic fluid), and birth defects.

- Thyroid disease in pregnancy can, if uncorrected, cause adverse effects on fetal and maternal well-being. The deleterious effects of thyroid dysfunction can also extend beyond pregnancy and delivery to affect neurointellectual development in the early life of the child. Demand for thyroid hormones is increased during pregnancy which may cause a previously unnoticed thyroid disorder to worsen.

- Untreated celiac disease can cause spontaneous abortion (miscarriage), intrauterine growth restriction, small for gestational age, low birthweight and preterm birth. Often reproductive disorders are the only manifestation of undiagnosed celiac disease and most cases are not recognized. Complications or failures of pregnancy cannot be explained simply by malabsorption, but by the autoimmune response elicited by the exposure to gluten, which causes damage to the placenta. The gluten-free diet avoids or reduces the risk of developing reproductive disorders in pregnant women with celiac disease. Also, pregnancy can be a trigger for the development of celiac disease in genetically susceptible women who are consuming gluten.

- Systemic lupus erythematosus in pregnancy confers an increased rate of fetal death "in utero," spontaneous abortion, and of neonatal lupus.

- Hypercoagulability in pregnancy is the propensity of pregnant women to develop thrombosis (blood clots). Pregnancy itself is a factor of hypercoagulability (pregnancy-induced hypercoagulability), as a physiologically adaptive mechanism to prevent "post partum" bleeding. However, in combination with an underlying hypercoagulable states, the risk of thrombosis or embolism may become substantial.

Intrauterine exposure to environmental toxins in pregnancy has the potential to cause adverse effects on the development of the embryo/fetus and to cause pregnancy complications. Air pollution has been associated with low birth weight infants. Conditions of particular severity in pregnancy include mercury poisoning and lead poisoning. To minimize exposure to environmental toxins, the "American College of Nurse-Midwives" recommends: checking whether the home has lead paint, washing all fresh fruits and vegetables thoroughly and buying organic produce, and avoiding cleaning products labeled "toxic" or any product with a warning on the label.

Pregnant women can also be exposed to toxins in the workplace, including airborne particles. The effects of wearing N95 filtering facepiece respirators are similar for pregnant women as non-pregnant women, and wearing a respirator for one hour does not affect the fetal heart rate.

Hypercoagulability in pregnancy is the propensity of pregnant women to develop thrombosis (blood clots). Pregnancy itself is a factor of hypercoagulability (pregnancy-induced hypercoagulability), as a physiologically adaptive mechanism to prevent "post partum" bleeding. However, when combined with an additional underlying hypercoagulable states, the risk of thrombosis or embolism may become substantial.

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.

Thyroid disease in pregnancy can, if uncorrected, cause adverse effects on fetal and maternal well-being. The deleterious effects of thyroid dysfunction can also extend beyond pregnancy and delivery to affect neurointellectual development in the early life of the child. Demand for thyroid hormones is increased during pregnancy which may cause a previously unnoticed thyroid disorder to worsen. The most effective way of screening for thyroid dysfunction is not known. A review found that more women were diagnosed with thyroid dysfunction when all pregnant women were tested instead of just testing those at ‘high-risk’ of thyroid problems (those with family history, signs or symptoms). Finding more women with thyroid dysfunction meant that the women could have treatment and management through their pregnancies. However the outcomes of the pregnancies were surprisingly similar so more research is needed to look at the effects of screening all women for thyroid problems.

In rare cases, inherited bleeding disorders, like hemophilia, von Willebrand disease (vWD), or factor IX or XI deficiency, may cause severe postpartum hemorrhage, with an increased risk of death particularly in the postpartum period. The risk of postpartum hemorrhage in patients with vWD and carriers of hemophilia has been found to be 18.5% and 22% respectively. This pathology occurs due to the normal physiological drop in maternal clotting factors after delivery which greatly increases the risk of secondary postpartum hemorrhage.

Another bleeding risk factor is thrombocytopenia, or decreased platelet levels, which is the most common hematological change associated with pregnancy induced hypertension. If platelet counts drop less than 100,000 per microliter the patient will be at a severe risk for inability to clot during and after delivery.

Antepartum bleeding (APH), also prepartum hemorrhage, is bleeding during pregnancy from the 24th week (sometimes defined as from the 20th week) gestational age to full term (40th week). The primary consideration is the presence of a placenta previa which is a low lying placenta at or very near to the internal cervical os. This condition occurs in roughly 4 out of 1000 pregnancies and usually needs to be resolved by delivering the baby via cesarean section. Also a placental abruption (in which there is premature separation of the placenta) can lead to obstetrical hemorrhage, sometimes concealed. This pathology is of important consideration after maternal trauma such as a motor vehicle accident or fall.

Other considerations to include when assessing antepartum bleeding are: sterile vaginal exams that are performed in order to assess dilation of the patient when the 40th week is approaching. As well as cervical insufficiency defined as a midtrimester (14th-26th week) dilation of the cervix which may need medical intervention to assist in keeping the pregnancy sustainable.

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.

Although it is very uncommon, women undergoing surgical abortion after 18 weeks gestation sometimes give birth to a fetus that may survive briefly. Longer term survival is possible after 22 weeks.

If medical staff observe signs of life, they may be required to provide care: emergency medical care if the child has a good chance of survival and palliative care if not. Induced fetal demise before termination of pregnancy after 20–21 weeks gestation is recommended to avoid this.

Death following live birth caused by abortion is given the ; data are identified as either fetus or newborn. Between 1999 and 2013, in the U.S., the CDC recorded 531 such deaths for newborns, approximately 4 per 100,000 abortions.

True cervical pregnancies tend to abort; if, however, the pregnancy is located higher in the canal and the placenta finds support in the uterine cavity it can go past the first trimester. With the placenta being implanted abnormally extensive vaginal bleeding can be expected at time of delivery and placental removal. While early cervical pregnancies may abort spontaneously or can be managed with excision, D&C, suturing, electrocautery, and tamponading, by medication such as methotrexate, and/or by uterine artery embolization, a more advanced pregnancy may require a hysterectomy to control bleeding. The more advanced the pregnancy the higher the risk for a major bleeding necessitating a hysterectomy.

On a very rare occasion, a cervical pregnancy results in the birth of a live baby, typically the pregnancy is in the upper part of the cervical canal and manages to extend into the lower part of the uterine cavity.

A cervical pregnancy can develop together with a normal intrauterine pregnancy; such a heterotopic pregnancy will call for expert management as to not to endanger the intrauterine pregnancy.

Interstitial pregnancies account for 2–4% of all tubal pregnancies, or for 1 in 2,500 to 5,000 live births. About one in fifty women with an interstitial pregnancy dies. Patients with an interstitial pregnancies have a 7-times higher mortality than those with ectopics in general. With the growing use of assisted reproductive technologies, the incidence of interstitial pregnancy is rising.

The rate of cancer during pregnancy is 0.02–1%, and in many cases, cancer of the mother leads to consideration of abortion to protect the life of the mother, or in response to the potential damage that may occur to the fetus during treatment. This is particularly true for cervical cancer, the most common type of which occurs in 1 of every 2,000–13,000 pregnancies, for which initiation of treatment "cannot co-exist with preservation of fetal life (unless neoadjuvant chemotherapy is chosen)". Very early stage cervical cancers (I and IIa) may be treated by radical hysterectomy and pelvic lymph node dissection, radiation therapy, or both, while later stages are treated by radiotherapy. Chemotherapy may be used simultaneously. Treatment of breast cancer during pregnancy also involves fetal considerations, because lumpectomy is discouraged in favor of modified radical mastectomy unless late-term pregnancy allows follow-up radiation therapy to be administered after the birth.

Exposure to a single chemotherapy drug is estimated to cause a 7.5–17% risk of teratogenic effects on the fetus, with higher risks for multiple drug treatments. Treatment with more than 40 Gy of radiation usually causes spontaneous abortion. Exposure to much lower doses during the first trimester, especially 8 to 15 weeks of development, can cause intellectual disability or microcephaly, and exposure at this or subsequent stages can cause reduced intrauterine growth and birth weight. Exposures above 0.005–0.025 Gy cause a dose-dependent reduction in IQ. It is possible to greatly reduce exposure to radiation with abdominal shielding, depending on how far the area to be irradiated is from the fetus.

The process of birth itself may also put the mother at risk. "Vaginal delivery may result in dissemination of neoplastic cells into lymphovascular channels, haemorrhage, cervical laceration and implantation of malignant cells in the episiotomy site, while abdominal delivery may delay the initiation of non-surgical treatment."

Patients with an ectopic pregnancy are generally at higher risk for a recurrence, however, there are no specific data for patients with an interstitial pregnancy. When a new pregnancy is diagnosed it is important to monitor the pregnancy by transvaginal sonography to assure that is it properly located, and that the surgically repaired area remains intact. Cesarean delivery is recommended to avoid uterine rupture during labor.

There are several potential risk factors or causes to this increased risk:

- An increased immune tolerance in pregnancy to prevent an immune reaction against the fetus

- Maternal physiological changes including a decrease in respiratory volumes and urinary stasis due to an enlarging uterus.

- The presence of a placenta for pathogens to use as a habitat, such as by "L. monocytogenes" and "P. falciparum".

In the United States, uterus didelphys is reported to occur in 0.1–0.5% of women. It is difficult to know the exact occurrence of this anomaly, as it may go undetected in the absence of medical and reproductive complications.

AS has a reported incidence of 25% of D&Cs performed 1–4 weeks post-partum, up to 30.9% of D&Cs performed for missed miscarriages and 6.4% of D&Cs performed for incomplete miscarriages. In another study, 40% of patients who underwent repeated D&C for retained products of conception after missed miscarriage or retained placenta developed AS.

In the case of missed miscarriages, the time period between fetal demise and curettage may increase the likelihood of adhesion formation due to fibroblastic activity of the remaining tissue.

The risk of AS also increases with the number of procedures: one study estimated the risk to be 16% after one D&C and 32% after 3 or more D&Cs. However, a single curettage often underlies the condition.

In an attempts to estimate the prevalence of AS in the general population, it was found in 1.5% of women undergoing hysterosalpingography HSG, and between 5 and 39% of women with recurrent miscarriage.

After miscarriage, a review estimated the prevalence of AS to be approximately 20% (95% confidence interval: 13% to 28%).