<unk>  may occur for many reasons, not all of which can be identified. Risk factors are those things that increase the likelihood of having a<unk>  but don't necessarily cause a<unk> . Up to 70 conditions, infections, medical procedures, lifestyle factors, occupational exposures, chemical exposure, and shift work are associated with increased risk for<unk> . Some of these risks include endocrine, genetic, uterine, or hormonal abnormalities, reproductive tract infections, and tissue rejection caused by an autoimmune disorder. Trimesters First trimester + Chromosomal abnormalities found in first trimester<unk> s Description Proportion of total Normal 45–55% Autosomal trisomy 22–32% Monosomy X (45, X) 5–20% Triploidy 6–8% Structural abnormality ofthe chromosome 2% Double or triple trisomy 0.7–2.0% Translocation Unknown Most clinically apparent<unk> s (two-thirds to three-quarters in various studies) occur during the first trimester. About 30% to 40% of all fertilized eggs miscarry, often before the pregnancy is known. The embryo typically dies before the pregnancy is expelled; bleeding into the decidua basalis and tissue necrosis causes uterine contractions to expel the pregnancy. Early<unk> s can be due to a developmental abnormality of the placenta or other embryonic tissues. In some instances an embryo does not form but other tissues do. This has been called a "blighted ovum". Successful implantation of the zygote into the uterus is most likely 8 to 10 days after fertilization. If the zygote has not implanted by day 10, implantation becomes increasingly unlikely in subsequent days. A chemical pregnancy is a pregnancy that was detected by testing but ends in<unk>  before or around the time of the next expected period. Chromosomal abnormalities are found in more than half of embryos miscarried in the first 13 weeks. Half of embryonic<unk> s (25% of all<unk> s) have an aneuploidy (abnormal number of chromosomes). Common chromosome abnormalities found in<unk> s include an autosomal trisomy (22–32%), monosomy X (5–20%), triploidy (6–8%), tetraploidy (2–4%), or other structural chromosomal abnormalities (2%). Genetic problems are more likely to occur with older parents; this may account for the higher rates observed in older women. Luteal phase progesterone deficiency may or may not be a contributing factor to<unk> . Second and third trimesters Second trimester losses may be due to maternal factors such as uterine malformation, growths in the uterus (fibroids), or cervical problems. These conditions also may contribute to premature birth. Unlike first-trimester<unk> s, second-trimester<unk> s are less likely to be caused by a genetic abnormality; chromosomal aberrations are found in a third of cases. Infection during the third trimester can cause a<unk> . Age The age of the pregnant woman is a significant risk factor.<unk>  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. Obesity, eating disorders and caffeine Not only is obesity associated with<unk> ; it can result in sub-fertility and other adverse pregnancy outcomes. Recurrent<unk>  is also related to obesity. Women with bulimia nervosa and anorexia nervosa may have a greater risk for<unk> . Nutrient deficiencies have not been found to impact<unk>  rates but hyperemesis gravidarum sometimes precedes a<unk> . Caffeine consumption also has been correlated to<unk>  rates, at least at higher levels of intake. However, such higher rates are statistically significant only in certain circumstances. Vitamin supplementation has generally not shown to be effective in preventing<unk> . Chinese traditional medicine has not been found to prevent<unk> . Endocrine disorders Disorders of the thyroid may affect pregnancy outcomes. Related to this, iodine deficiency is strongly associated with an increased risk of<unk> . The risk of<unk>  is increased in those with poorly controlled insulin-dependent diabetes mellitus. Women with well-controlled diabetes have the same risk of<unk>  as those without diabetes. Food poisoning Ingesting food that has been contaminated with listeriosis, toxoplasmosis, and salmonella is associated with an increased risk of<unk> . Amniocentesis and chorionic villus sampling Amniocentesis and chorionic villus sampling (CVS) are procedures conducted to assess the fetus. A sample of amniotic fluid is obtained by the insertion of a needle through the abdomen and into the uterus. Chorionic villus sampling is a similar procedure with a sample of tissue removed rather than fluid. These procedures are not associated with pregnancy loss during the second trimester but they are associated with<unk> s and birth defects in the first trimester.<unk>  caused by invasive prenatal diagnosis (chorionic villus sampling (CVS) and amniocentesis) is rare (about 1%). Surgery The effects of surgery on pregnancy are not well-known including the effects of bariatric surgery. Abdominal and pelvic surgery are not risk factors for<unk> . Ovarian tumours and cysts that are removed have not been found to increase the risk of<unk> . The exception to this is the removal of the corpus luteum from the ovary. This can cause fluctuations in the hormones necessary to maintain the pregnancy. Medications There is no significant association between antidepressant medication exposure and spontaneous abortion. The risk of<unk>  is not likely decreased by discontinuing SSRIs prior to pregnancy. Some available data suggest that there is a small increased risk of<unk>  for women taking any antidepressant, though this risk becomes less statistically significant when excluding studies of poor quality. Medicines that increase the risk of<unk>  include: * retinoids * nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen * misoprostol * methotrexate * statins Immunizations Immunizations have not been found to cause<unk> . Live vaccinations, like the MMR vaccine, can theoretically cause damage to the fetus as the live virus can cross the placenta and potentially increase the risk for<unk> . Therefore, the Center for Disease Control (CDC) recommends against pregnant women receiving live vaccinations. However, there is no clear evidence that has shown live vaccinations to increase the risk for<unk>  or fetal abnormalities. Some live vaccinations include: MMR, varicella, certain types of the influenza vaccine, and rotavirus. Treatments for cancer Ionizing radiation levels given to a woman during cancer treatment cause<unk> . Exposure can also impact fertility. The use of chemotherapeutic drugs used to treat childhood cancer increases the risk of future<unk> . Pre-existing diseases Several pre-existing diseases in pregnancy can potentially increase the risk of<unk> , including diabetes, polycystic ovary syndrome (PCOS), hypothyroidism, certain infectious diseases, and autoimmune diseases. PCOS may increase the risk of<unk> . Two studies suggested treatment with the drug metformin significantly lowers the rate of<unk>  in women with PCOS, but the quality of these studies has been questioned. Metformin treatment in pregnancy has not been shown to be safe. In 2007 the Royal College of Obstetricians and Gynaecologists also recommended against use of the drug to prevent<unk> . Thrombophilias or defects in coagulation and bleeding were once thought to be a risk in<unk>  but have been subsequently questioned. Severe cases of hypothyroidism increase the risk of<unk> . The effect of milder cases of hypothyroidism on<unk>  rates has not been established. A condition called luteal phase defect (LPD) is a failure of the uterine lining to be fully prepared for pregnancy. This can keep a fertilized egg from implanting or result in<unk> . Mycoplasma genitalium infection is associated with increased risk of preterm birth and<unk> . Infections can increase the risk of a<unk> : rubella (German measles), cytomegalovirus, bacterial vaginosis, HIV, chlamydia, gonorrhoea, syphilis, and malaria. Immune status Autoimmunity is a possible cause of recurrent or late-term<unk> s. In the case of an autoimmune-induced<unk> , the woman's body attacks the growing fetus or prevents normal pregnancy progression. Autoimmune disease may cause abnormalities in embryos, which in turn may lead to<unk> . As an example, Celiac disease increases the risk of<unk>  by an odds ratio of approximately 1.4. A disruption in normal immune function can lead to the formation of antiphospholipid antibody syndrome. This will affect the ability to continue the pregnancy, and if a woman has repeated<unk> s, she can be tested for it. Approximately 15% of recurrent<unk> s are related to immunologic factors. The presence of anti-thyroid autoantibodies is associated with an increased risk with an odds ratio of 3.73 and 95% confidence interval 1.8–7.6. Having lupus also increases the risk for<unk> . Anatomical defects and trauma Fifteen per cent of women who have experienced three or more recurring<unk> s have some anatomical defect that prevents the pregnancy from being carried for the entire term. The structure of the uterus affects the ability to carry a child to term. Anatomical differences are common and can be congenital. Type of uterinestructure<unk>  rateassociated with defect References Bicornate uterus 40–79% Septate or unicornate 34–88% Arcuate Unknown Didelphys 40% Fibroids Unknown In some women, cervical incompetence or cervical insufficiency occurs with the inability of the cervix to stay closed during the entire pregnancy. It does not cause first trimester<unk> s. In the second trimester, it is associated with an increased risk of<unk> . It is identified after a premature birth has occurred at about
Miscarriage
Ectopic pregnancy
Recurrent miscarriage
Implantation bleeding
Stillbirth
Forced pregnancy
Dry sex
Pregnancy loss