Ionizing radiation levels given to a woman during cancer treatment cause miscarriage. Exposure can also impact fertility. The use of chemotherapeutic drugs used to treat childhood cancer increases the risk of miscarriage.

The apprehension is not necessarily data driven and is a cautionary response to the lack of clinical studies in pregnant women. The indication is a trade-off between the adverse effects of the drug, the risks associated with intercurrent diseases and pregnancy complications, and the efficiency of the drug to prevent or ameliorate such risks. In some cases, the use of drugs in pregnancy carries benefits that outweigh the risks. For example, high fever is harmful for the fetus in the early months, thus the use of paracetamol (acetaminophen) is generally associated with lower risk than the fever itself. Similarly, diabetes mellitus during pregnancy may need intensive therapy with insulin to prevent complications to mother and baby. Pain management for the mother is another important area where an evaluation of the benefits and risks is needed. NSAIDs such as Ibuprofen and Naproxen are probably safe for use for a short period of time, 48–72 hours, once the mother has reached the second trimester. If taking aspirin for pain management the mother should never take a dose higher than 100 mg.

U.S. Code of Federal Regulations requires that certain drugs and biological products must be labelled very specifically with respect to their effects on pregnant populations, including a definition of a "pregnancy category." These rules are enforced by the Food and Drug Administration (FDA). The FDA does not regulate labelling for all hazardous and non-hazardous substances and some potentially hazardous substances are not assigned a pregnancy category.

Australia’s categorisations system takes into account the birth defects, the effects around the birth or when the mother gives birth, and problems that will arise later in the child's life caused from the drug taken. The system places them into a category of their severity that the drug could cause to the infant when it crosses the placenta(Australian Government, 2014).

Immunizations have not been found to cause miscarriage. There is no significant association between antidepressant medication exposure and spontaneous abortion. The risk of miscarriage is not likely decrease by discontinuing SSRI prior to pregnancy. Some available data suggest that there is a small increased risk of miscarriage for women taking any antidepressant, though this risk becomes less statistically significant when excluding studies of poor quality.

Medicines that increase the risk of miscarriage include:

- retinoids

- nonsteroidal anti-inflammatory drugs (NSAIDs) , such as ibuprofen

- misoprostol

- methotrexate

The use of recreational drugs in pregnancy can cause various pregnancy complications.

- Ethanol during pregnancy can cause fetal alcohol syndrome and fetal alcohol spectrum disorder. Studies have shown that light to moderate drinking during pregnancy might not pose a risk to the fetus, although no amount of alcohol during pregnancy can be guaranteed to be absolutely safe.

- Tobacco smoking during pregnancy can cause a wide range of behavioral, neurological, and physical difficulties. Smoking during pregnancy causes twice the risk of premature rupture of membranes, placental abruption and placenta previa. Smoking is associated with 30% higher odds of preterm birth.

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

- Prenatal methamphetamine exposure can cause premature birth and congenital abnormalities. Short-term neonatal outcomes show small deficits in infant neurobehavioral function and growth restriction. Long-term effects in terms of impaired brain development may also be caused by methamphetamine use.

- Cannabis in pregnancy has been shown to be teratogenic in large doses in animals, but has not shown any teratogenic effects in humans.

Nutrition during pregnancy is important to ensure healthy growth of the fetus. Nutrition during pregnancy is different from the non-pregnant state. There are increased energy requirements and specific micronutrient requirements. Women benefit from education to encourage a balanced energy and protein intake during pregnancy. Some women may need professional medical advice if their diet is affected by medical conditions, food allergies, or specific religious/ ethical beliefs.

Adequate periconceptional (time before and right after conception) folic acid (also called folate or Vitamin B) intake has been shown to decrease the risk of fetal neural tube defects, such as spina bifida. The neural tube develops during the first 28 days of pregnancy, a urine pregnancy test is not usually positive until 14 days post-conception, explaining the necessity to guarantee adequate folate intake before conception. Folate is abundant in green leafy vegetables, legumes, and citrus. In the United States and Canada, most wheat products (flour, noodles) are fortified with folic acid.

DHA omega-3 is a major structural fatty acid in the brain and retina, and is naturally found in breast milk. It is important for the woman to consume adequate amounts of DHA during pregnancy and while nursing to support her well-being and the health of her infant. Developing infants cannot produce DHA efficiently, and must receive this vital nutrient from the woman through the placenta during pregnancy and in breast milk after birth.

Several micronutrients are important for the health of the developing fetus, especially in areas of the world where insufficient nutrition is common. Women living in low and middle income countries are suggested to take multiple micronutrient supplements containing iron and folic acid. These supplements have been shown to improve birth outcomes in developing countries, but do not have an effect on perinatal mortality. Adequate intake of folic acid, and iron is often recommended. In developed areas, such as Western Europe and the United States, certain nutrients such as Vitamin D and calcium, required for bone development, may also require supplementation. Vitamin E supplementation has not been shown to improve birth outcomes. Zinc supplementation has been associated with a decrease in preterm birth, but it is unclear whether it is causative. Daily iron supplementation reduces the risk of maternal anemia. Studies of routine daily iron supplementation for pregnant women found improvement in blood iron levels, without a clear clinical benefit. The nutritional needs for women carrying twins or triplets. are higher than those of women carrying one baby.

Women are counseled to avoid certain foods, because of the possibility of contamination with bacteria or parasites that can cause illness. Careful washing of fruits and raw vegetables may remove these pathogens, as may thoroughly cooking leftovers, meat, or processed meat. Unpasteurized dairy and deli meats may contain "Listeria," which can cause neonatal meningitis, stillbirth and miscarriage. Pregnant women are also more prone to "Salmonella" infections, can be in eggs and poultry, which should be thoroughly cooked. Cat feces and undercooked meats may contain the parasite Toxoplasma gondii and can cause toxoplasmosis. Practicing good hygiene in the kitchen can reduce these risks.

Women are also counseled to eat seafood in moderation and to eliminate seafood known to be high in mercury because of the risk of birth defects. Pregnant women are counseled to consume caffeine in moderation, because large amounts of caffeine are associated with miscarriage. However, the relationship between caffeine, birthweight, and preterm birth is unclear.

The data presented is for comparative and illustrative purposes only, and may have been superseded by updated data.

Adoption of specific professional policies can immediately reduce risk of preterm birth as the experience in assisted reproduction has shown when the number of embryos during embryo transfer was limited.

Many countries have established specific programs to protect pregnant women from hazardous or night-shift work and to provide them with time for prenatal visits and paid pregnancy-leave. The EUROPOP study showed that preterm birth is not related to type of employment, but to prolonged work (over 42 hours per week) or prolonged standing (over 6 hours per day). Also, night work has been linked to preterm birth. Health policies that take these findings into account can be expected to reduce the rate of preterm birth.

Preconceptional intake of folic acid is recommended to reduce birth defects. There is significant evidence that long-term (> one year) use of folic acid supplement preconceptionally may reduce premature birth. Reducing smoking is expected to benefit pregnant women and their offspring.

Healthy eating can be instituted at any stage of the pregnancy including nutritional adjustments, use of vitamin supplements, and smoking cessation. Calcium supplementation in women who have low dietary calcium reduces the number of negative outcomes including preterm birth, pre-eclampsia, and maternal death. The World Health Organization (WHO) suggests 1.5-2 g of calcium supplements daily, for pregnant women who have low levels calcium in their diet. Supplemental intake of C and E vitamins have not been found to reduce preterm birth rates. Different strategies are used in the administration of prenatal care, and future studies need to determine if the focus can be on screening for high-risk women, or widened support for low-risk women, or to what degree these approaches can be merged. While periodontal infection has been linked with preterm birth, randomized trials have not shown that periodontal care during pregnancy reduces preterm birth rates.

Some doctors recommend complete bed-rest for the mother coupled with massive intakes of protein as a therapy to try to counteract the syndrome. Research completed shows these nutritional supplements do work. Diet supplementation was associated with lower overall incidence of TTTS (20/52 versus 8/51, P = 0.02) and with lower prevalence of TTTS at delivery (18/52 versus 6/51, P = 0.012) when compared with no supplementation. Nutritional intervention also significantly prolonged the time between the diagnosis of TTTS and delivery (9.4 ± 3.7 weeks versus 4.6 ± 6.5 weeks; P = 0.014). The earlier nutritional regimen was introduced, the lesser chance of detecting TTTS ( P = 0.001). Although not statistically significant, dietary intervention was also associated with lower Quintero stage, fewer invasive treatments, and lower twin birth weight discordance. Diet supplementation appears to counter maternal metabolic abnormalities in monochorionic twin pregnancies and improve perinatal outcomes in TTTS when combined with the standard therapeutic options. Nutritional therapy appears to be most effective in mitigating cases that are caught in Quintero Stage I, little effect has been observed in those that are beyond Stage I.

This procedure involves the tearing of the dividing membrane between fetuses such that the amniotic fluid of both twins mixes under the assumption that pressure is different in either amniotic sac and that its equilibration will ameliorate progression of the disease. It has not been proven that pressures are different in either amniotic sac. Use of this procedure can preclude use of other procedures as well as make difficult the monitoring of disease progression. In addition, tearing the dividing membrane has contributed to cord entanglement and demise of fetuses through physical complications.

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."

The pregnancy category of a medication is an assessment of the risk of fetal injury due to the pharmaceutical, if it is used as directed by the mother during pregnancy. It does "not" include any risks conferred by pharmaceutical agents or their metabolites in breast milk.

Every drug has specific information listed in its product literature. The British National Formulary used to provide a table of drugs to be avoided or used with caution in pregnancy, and did so using a limited number of key phrases, but now Appendix 4 (which was the Pregnancy table) has been removed. Appendix 4 is now titled "Intravenous Additives". However, information that was previously available in the former Appendix 4 (pregnancy) and Appendix 5 (breast feeding) is now available in the individual drug monographs.

Continuing glucocorticoids at the lowest effective dose and/or cautious use of azathioprine may be preferred in some patients, but needs to be weighed against potential adverse effects of such medications.

Spontaneous abortion occurs in various animals. For example, in sheep, it may be caused by crowding through doors, or being chased by dogs. In cows, abortion may be caused by contagious disease, such as brucellosis or "Campylobacter", but can often be controlled by vaccination. Eating pine needles can also induce abortions in cows. In horses, a fetus may be aborted or resorbed if it has lethal white syndrome (congenital intestinal aganglionosis). Foal embryos that are homozygous for the dominant white gene (WW) are theorized to also be aborted or resorbed before birth. In many species of sharks and rays, stress induced abortions occur frequently on capture.

Viral infection can cause abortion in dogs. Cats can experience spontaneous abortion for many reasons, including hormonal imbalance. A combined abortion and spaying is performed on pregnant cats, especially in Trap-Neuter-Return programs, to prevent unwanted kittens from being born.

Female rodents may terminate a pregnancy when exposed to the smell of a male not responsible for the pregnancy, known as the Bruce effect.

Abortion may also be induced in animals, in the context of animal husbandry. For example, abortion may be induced in mares that have been mated improperly, or that have been purchased by owners who did not realize the mares were pregnant, or that are pregnant with twin foals. Feticide can occur in horses and zebras due to male harassment of pregnant mares or forced copulation, although the frequency in the wild has been questioned. Male gray langur monkeys may attack females following male takeover, causing miscarriage.

Talking with a health care provider before becoming pregnant is recommended. They may suggest to wait until the disease is in remission or suggest a change in medication before becoming pregnant. There are endocrinologists that specialize in treating women with high-risk pregnancies.

Some women with autoimmune diseases may have problems getting pregnant. This can happen for many reasons. Tests can tell if fertility problems are caused by an autoimmune disease or an unrelated reason. Fertility treatments are able to help some women with autoimmune disease become pregnant.

Hormonal and other changes in pregnancy affect physical performance. In the first three months it is known that a woman’s body produces a natural surplus of red blood cells, which are well supplied with oxygen-carrying hemoglobin, in order to support the growing fetus. A study of athletes before and after pregnancy by Professor James Pivarnik at the Human Energy Research laboratory in Michigan State University has found there is a 60 per cent increase in blood volume and that this could improve the body’s ability to carry oxygen to muscles by up to 30 percent. This would have obvious positive effects on aerobic capacity. Other potential advantages are obtained from the surge in hormones that pregnancy induces, predominantly progesterone and estrogen, but also testosterone, which could increase muscle strength. Increases in hormones like relaxin, which loosens the hip joints to prepare for childbirth, may have a performance-enhancing effect on joint mobility.

Several world records have been set by female athletes shortly after giving birth to their first child. This is accepted as a natural and unintended event.

Testing for abortion doping is virtually impossible, as the only things to test for are the athletes’ own naturally enriched blood and hormones. While abortion doping is officially banned under United States Olympic rules, there is no ban on getting pregnant. If an athlete was accused of abortion doping, she could simply argue that the pregnancy was not induced for the temporary physiological benefits. It remains unknown how common the procedure is, and it has yet to be proven if it has been purposely implemented at all. Opinions vary greatly; it is regarded as completely unfounded by some and is accepted as a worldwide athletic phenomenon by others.

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.

Most women with GTD can become pregnant again and can have children again. The risk of a further molar pregnancy is low. More than 98% of women who become pregnant following a molar pregnancy will not have a further hydatidiform mole or be at increased risk of complications.

In the past, it was seen as important not to get pregnant straight away after a GTD. Specialists recommended a waiting period of 6 months after the hCG levels become normal. Recently, this standpoint has been questioned. New medical data suggest that a significantly shorter waiting period after the hCG levels become normal is reasonable for approximately 97% of the patients with hydatidiform mole.

The risk of a repeat GTD is approximately 1 in 100, compared with approximately 1 in 1000 risk in the general population. Especially women whose hCG levels remain significantly elevated are at risk of developing a repeat GTD.

Although most autoimmune diseases cannot be cured, it is possible to manage the disease and participate in same activities that other women are able to do. Women with autoimmune diseases lead full, active lives. Seeing a specialist will assist in maintaining function and the maintenance of optimal health.

Rh disease (also known as rhesus isoimmunisation, Rh (D) disease, rhesus incompatibility, rhesus disease, RhD hemolytic disease of the newborn, rhesus D hemolytic disease of the newborn or RhD HDN) is a type of hemolytic disease of the newborn (HDN). The disease ranges from mild to severe, and typically occurs only in some second or subsequent pregnancies of Rh negative women where the fetus's father is Rh positive, leading to a Rh+ pregnancy. During birth, the mother may be exposed to the infant's blood, and this causes the development of antibodies, which may affect the health of subsequent Rh+ pregnancies. In mild cases, the fetus may have mild anaemia with reticulocytosis. In moderate or severe cases the fetus may have a more marked anaemia and erythroblastosis fetalis (hemolytic disease of the newborn). When the disease is very severe it may cause hydrops fetalis or stillbirth.

Rh disease is generally preventable by treating the mother during pregnancy or soon after delivery with an intramuscular injection of anti-RhD immunoglobulin (Rho(D) immune globulin). The RhD protein is coded by the RHD gene.

For women with systemic lupus erythematosus (SLE), pregnancy can present some particular challenges for both mother and child.

While most infants born to mothers who have SLE are healthy, mothers with SLE as an intercurrent disease in pregnancy should remain under medical care until delivery. In general, women with SLE and, in addition, hypertension, proteinuria, and azotemia have an extra increased risk for pregnancy complications. Pregnancy outcomes in women with SLE who receive renal transplants are similar to those of transplant recipients without SLE.

Women pregnant and known to have anti-Ro (SSA) or anti-La antibodies (SSB) often have echocardiograms during the 16th and 30th weeks of pregnancy to monitor the health of the heart and surrounding vasculature.

Contraception and other reliable forms of pregnancy prevention is routinely advised for women with SLE, since getting pregnant during active disease was found to be harmful. Lupus nephritis was the most common manifestation.

Of live births, approximately one third are delivered prematurely.

Currently, the only reliable way to prevent GBS-EOD is intrapartum antibiotic prophylaxis (IAP) - administration of antibiotics during delivery. Intravenous penicillin or ampicillin given at the onset of labour and then again every four hours until delivery to GBS colonized women have been proven to be very effective at preventing vertical transmission of GBS from mother to baby and GBS-EOD

(penicillin G, 5 million units IV initial dose, then 2.5–3.0 million units every 4 hours until delivery or ampicillin, 2 g IV initial dose, then 1 g IV every 4 hours until delivery).

Penicillin-allergic women without a history of anaphylaxis (angioedema, respiratory distress, or urticaria) following administration of a penicillin or a cephalosporin (low risk of anaphylaxis) could receive cefazolin (2 g IV initial dose, then 1 g IV every 8 hours until delivery) instead of penicillin or ampicillin. Clindamycin (900 mg IV every 8 hours until delivery), and vancomycin (1 g IV every 12 hours until delivery) are used to prevent GBS-EOD in infants born to penicillin-allergic mothers. Erythromycin is not recommended under any circumstances today.

Antibiotic susceptibility testing of GBS isolates is crucial for appropriate antibiotic selection for IAP in penicillin-allergic women, because resistance to clindamycin, the most common agent used (in penicillin-allergic women), is increasing among GBS isolates. Appropriate methodologies for testing are important, because resistance to clyndamicin (antimicrobial resistance) can occur in some GBS strains that appear susceptible (antibiotic sensitivity) in certain susceptibility tests.

If appropriate IAP in GBS colonized women starts at least 2 hours before the delivery, the risk of neonatal infection is also somehow reduced.

True penicillin allergy is rare with an estimated frequency of anaphylaxis of one to five episodes per 10,000 cases of penicillin therapy. Penicillin administered to a woman with no history of β-lactam allergy has a risk of anaphylaxis of 0.04 to 4 per 100,000. Maternal anaphylaxis associated with GBS IAP occurs, but any morbidity associated with anaphylaxis is offset greatly by reductions in the incidence of GBS-EOD.

Home births are becoming increasingly popular in the UK. Recommendations for preventing GBS infections in newborns are the same for home births as for hospital births. Around 25% of women having home births probably carry GBS in their vaginas at delivery without knowing, and it could be difficult to follow correctly the recommendations of IAP and to deal with the risk of a severe allergic reaction to the antibiotics outside of a hospital setting.

IAPs have been considered to be associated with the emergence of resistant bacterial strains and with an increase in the incidence of early-onset infections caused by other pathogens, mainly Gram-negative bacteria such as "Escherichia coli". Nevertheless, most studies have not found an increased rate of non-GBS early-onset sepsis related to the widespread use of IAP.

Other strategies to prevent GBS-EOD have been studied, and chlorhexidine intrapartum vaginal cleansing has been proposed to help preventing GBS-EOD, nevertheless no evidence has been shown for the effectiveness of this approach.