disability including cerebral palsy. it has been reported that asymptomatic colonization of the decidua occurs in up to 70% of women at term using a dna probe suggesting that the presence of micro-organism alone may be insufficient to initiate the infectious response. as the condition is more prevalent in black women in the u.s. and the uk, it has been suggested to be an explanation for the higher rate of preterm birth in these populations. it is opined that bacterial vaginosis before or during pregnancy may affect the decidual inflammatory response that leads to preterm birth. the condition known as aerobic vaginitis can be a serious risk factor for preterm labor; several previous studies failed to acknowledge the difference between aerobic vaginitis and bacterial vaginosis, which may explain some of the contradiction in the results. untreated yeast infections are associated with preterm birth. a review into prophylactic antibiotics (given to prevent infection) in the second and third trimester of pregnancy (13–42 weeks of pregnancy) found a reduction in the number of preterm births in women with bacterial vaginosis. these antibiotics also reduced the number of waters breaking before labor in full-term pregnancies, reduced the risk of infection of the lining of the womb after delivery (endometritis), and rates of gonococcal infection. however, the women without bacterial vaginosis did not have any reduction in preterm births or pre-labor preterm waters breaking. much of the research included in this review lost participants during follow-up so did not report the long-term effects of the antibiotics on mothers or babies. more research in this area is needed to find the full effects of giving antibiotics throughout the second and third trimesters of pregnancy. a number of maternal bacterial infections are associated with preterm birth including pyelonephritis, asymptomatic bacteriuria, pneumonia, and appendicitis. a review into giving antibiotics in pregnancy for asymptomatic bacteriuria (urine infection with no symptoms) found the research was of very low quality but that it did suggest that taking antibiotics reduced the numbers of preterm births and babies with low birth weight. another review found that one dose of antibiotics did not seem as effective as a course of antibiotics but fewer women reported side effects from one dose. this review recommended that more research is needed to discover the best way of treating asymptomatic bacteriuria. a different review found that preterm births happened less for pregnant women who had routine testing for low genital tract infections than for women who only had testing when they showed symptoms of low genital tract infections. the women being routinely tested also gave birth to fewer babies with a low birth weight. even though these results look promising, the review was only based on one study so more research is needed into routine screening for low genital tract infections. also periodontal disease has been shown repeatedly to be linked to preterm birth. in contrast, viral infections, unless accompanied by a significant febrile response, are considered not to be a major factor in relation to preterm birth. genetics there is believed to be a maternal genetic component in preterm birth. estimated heritability of timing-of-birth in women was 34%. however, the occurrence of preterm birth in families does not follow a clear inheritance pattern, thus supporting the idea that preterm birth is a non-mendelian trait with a polygenic nature. prenatal care the absence of prenatal care has been associated with higher rates of preterm births. analysis of 15,627,407 live births in the united states in 1995–1998 concluded that the absence of prenatal care carried a 2.9 (95%ci 2.8, 3.0) times higher risk of preterm births. this same study found statistically significant relative risks of maternal anemia, intrapartum fever, unknown bleeding, renal disease, placental previa, hydramnios, placenta abruption, and pregnancy-induced hypertension with the absence of prenatal care. all these prenatal risks were controlled for other high-risk conditions, maternal age, gravidity, marital status, and maternal education. the absence of prenatal care prior to and during the pregnancy is primarily a function of socioeconomic factors (low family income and education), access to medical consultations (large distance from the place of residence to the healthcare unit and transportation costs), quality of healthcare, and social support. efforts to decrease rates of preterm birth should aim to increase the deficits posed by the aforementioned barriers and to increase access to prenatal care. diagnosis placental alpha microglobulin-1 placental alpha microglobulin-1 (pamg-1) has been the subject of several investigations evaluating its ability to predict imminent spontaneous preterm birth in women with signs, symptoms, or complaints suggestive of preterm labor. in one investigation comparing this test to fetal fibronectin testing and cervical length measurement via transvaginal ultrasound, the test for pamg-1 (commercially known as the partosure test) has been reported to be the single best predictor of imminent spontaneous delivery within 7 days of a patient presenting with signs, symptoms, or complaints of preterm labor. specifically, the ppv, or positive predictive value, of the tests were 76%, 29%, and 30% for pamg-1, ffn and cl, respectively (p < 0.01). fetal fibronectin fetal fibronectin (ffn) has become an important biomarker—the presence of this glycoprotein in the cervical or vaginal secretions indicates that the border between the chorion and decidua has been disrupted. a positive test indicates an increased risk of preterm birth, and a negative test has a high predictive value. it has been shown that only 1% of women in questionable cases of preterm labor delivered within the next week when the test was negative. ultrasound further information: cervical incompetence obstetric ultrasound has become useful in the assessment of the cervix in women at risk for premature delivery. a short cervix preterm is undesirable: a cervical length of less than 25 mm (0.98 in) at or before 24 weeks of gestational age is the most common definition of cervical incompetence. classification stages in prenatal development, with weeks and months numbered from last menstruation in humans, the usual definition of preterm birth is birth before a gestational age of 37 complete weeks. in the normal human fetus, several organ systems mature between 34 and 37 weeks, and the fetus reaches adequate maturity by the end of this period. one of the main organs greatly affected by premature birth is the lungs. the lungs are one of the last organs to mature in the womb; because of this, many premature babies spend the first days and weeks of their lives on ventilators. therefore, a significant overlap exists between preterm birth and prematurity. generally, preterm babies are premature and term babies are mature. preterm babies born near 37 weeks often have no problems relating to prematurity if their lungs have developed adequate surfactant, which allows the lungs to remain expanded between breaths. sequelae of prematurity can be reduced to a small extent by using drugs to accelerate maturation of the fetus, and to a greater extent by preventing preterm birth. prevention historically efforts have been primarily aimed to improve survival and health of preterm infants (tertiary intervention). such efforts, however, have not reduced the incidence of preterm birth. increasingly primary interventions that are directed at all women, and secondary intervention that reduce existing risks are looked upon as measures that need to be developed and implemented to prevent the health problems of premature infants and children. smoking bans are effective in decreasing preterm births. 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. before pregnancy 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 also some evidence that folic acid supplement preconceptionally (before becoming pregnant) may reduce premature birth. reducing smoking is expected to benefit pregnant women and their offspring. during pregnancy self-care methods to reduce the risk of preterm birth include proper nutrition, avoiding stress, seeking appropriate medical care, avoiding infections, and the control of preterm birth risk factors (e.g. working long hours while standing on feet, carbon monoxide exposure, domestic abuse, and other factors). reducing physical activity during pregnancy has not been shown to reduce the risk of a preterm birth. healthy eating can be instituted at any stage of the pregnancy including nutritional adjustments and consuming suggested vitamin supplements. calcium supplementation in women who have low dietary calcium may reduce 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 of calcium in their diet. supplemental intake of c and e vitamins have not been found to reduce preterm birth rates. while periodontal infection has been linked with preterm birth, randomized trials have not shown that periodontal care during pregnancy reduces preterm birth rates. smoking cessation has also been shown to reduce the risk. the use of personal at home uterine monitoring devices to detect contractions and possible preterm births in women at higher risk of having a preterm baby have been suggested. these home monitors may not reduce the number of preterm births, however, using these devices may increase the number of unplanned antenatal visits and may reduce the number of babies admitted to special care when compared with women receiving normal antenatal care. support from medical professionals, friends, and family during pregnancy may be beneficial at reducing caesarean birth and may reduce prenatal hospital admissions, however, these social supports alone may not prevent preterm birth. screening during pregnancy screening for asymptomatic bacteriuria followed by appropriate treatment reduces pyelonephritis and reduces the risk of preterm birth. extensive studies have been carried out to determine if other forms of screening in low-risk women followed by appropriate intervention are beneficial, including screening for and treatment of ureaplasma urealyticum, group b streptococcus, trichomonas vaginalis, and bacterial vaginosis did not reduce the rate of preterm birth. routine ultrasound examination of the length of the cervix may identify women at risk of preterm labour and tentative evidence suggests ultrasound measurement of the length of the cervix in those with preterm labor can help adjust management and results in the extension of pregnancy by about four days. screening for the presence of fibronectin in vaginal secretions is not recommended at this time in women at low risk of preterm birth. reducing existing risks women are identified to be at increased risk for preterm birth on the basis of their past obstetrical history or the presence of known risk factors. preconception intervention can be helpful in selected patients in a number of ways. patients with certain uterine anomalies may have a surgical correction (i.e. removal of a uterine septum), and those with certain medical problems can be helped by optimizing medical therapies prior to conception, be it for asthma, diabetes, hypertension, and others. multiple pregnancies in multiple pregnancies, which often result from use of assisted reproductive technology, there is a high risk of preterm birth. selective reduction is used to reduce the number of fetuses to two or three. reducing indicated preterm birth a number of agents have been studied for the secondary prevention of indicated preterm birth. trials using low-dose aspirin, fish oil, vitamin c and e, and calcium to reduce preeclampsia demonstrated some reduction in preterm birth only when low-dose aspirin was used. even if agents such as calcium or antioxidants were able to reduce preeclampsia, a resulting decrease in preterm birth was not observed. reducing spontaneous preterm birth reduction in activity by the mother—pelvic rest, limited work, bed rest—may be recommended although there is no evidence it is useful with some concerns it is harmful.