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Patient factors associated with the risk of spontaneous preterm birth.


Although the rate of preterm delivery has decreased consistently over the past 7 years in the United States through 2013, (1) preterm birth (PTB) remains the leading cause of neonatal and infant deaths. (2) Several risk factors for preterm delivery have been described, including social, personal, and economic characteristics; medical and pregnancy conditions; and behavioral factors. (3) Prevention of preterm delivery can be divided into primary prevention, secondary prevention, and tertiary prevention, where primary prevention (or prevention of a disease before it occurs) is focused on women with known risk factors. (4) Unfortunately, many risk factors for preterm delivery, such as race or bleeding, are non-modifiable. In this context our objective is to review modifiable, potentially modifiable, and non-modifiable risk factors for preterm delivery (table i).

Modifiable risk factors

Body mass index (BMI)

For many years we have acknowledged the relationship between low BMI and an increased risk of spontaneous PTB. (5,6) However, we now have data to suggest that high and low BMI are both associated with an increase in PTB. (7,8) A study conducted by Cnattingius and colleagues in Sweden demonstrated maternal overweight and obesity during pregnancy were associated with increased risks of preterm delivery, especially extremely preterm delivery. As for the relationship of underweight to the risk of PTB, Girsen and colleagues showed an inversely proportional relationship between BMI and the rate of PTB. (8) They found that the lower the BMI, the higher the risk of PTB, with a 61% relative increase in the rate of preterm delivery for women with a BMI of less than 16 kg/[m.sup.2]. Gestational weight gain also modifies the risk of preterm delivery in women with a low BMI. (9) Underweight women with poor weight gain have a 6- to 7-fold increased risk of preterm delivery compared with normal-weight women who gain an average amount of weight. Obesity, previously thought to be protective, (5) is also a risk factor for spontaneous preterm delivery. (7) The proposed mechanism is through increased inflammation via adipokines in visceral fat. The mechanism through which extremes of BMI may lead to preterm delivery may be attributable to nutritional status. For example, women with low serum folate concentrations have been shown to have increased rates of preterm delivery, (10) and obesity is linearly correlated with lower concentrations of folic acid. (11)


Maternal smoking has been linked consistently with an increased risk of PTB, along with other poor pregnancy outcomes. (12-14) The exact mechanism is unknown, but a proposed mechanism relates to the vasoconstrictive properties of nicotine on uterine blood flow. (6) Investigators have also shown that smoking cessation mitigates the risk of preterm delivery, (15,16) making this an important modifiable risk factor to address prior to and during pregnancy.

Potentially modifiable risk factors

Multiple gestation

Multiple gestation is a well-recognized risk factor for PTB, increasing the risk of this complication up to 6-fold. (6) While these pregnancies only account for 2% to 3% of infants, they disproportionally account for 15% to 20% of PTBs. (17) It is thought that the antecedent to preterm delivery in multiples is uterine overdistention. (18,19) Currently, there are no established therapies to reduce the risk of preterm delivery in higher order multiples. (20) Pregnancies conceived of by assisted reproductive technologies are also at increased risk to be twins or higher order multiple gestations. A higher fetal number is associated with an earlier gestational age at delivery. Multifetal pregnancy reduction of higher order multiples to a twin gestation is an option for some women to decrease the risk of prematurity, (21) though reduction of twins to a singleton is controversial. (22)

Short or prolonged interpregnancy interval

The literature suggests that extremes of interpregnancy interval, defined as time from delivery to next pregnancy, increase the risk for preterm delivery. (17,23,24) An interpregnancy interval of <6 months in one series conferred a 2-fold increase in risk for preterm delivery. (23) Authors also found an increase in neonatal deaths for this short interval. At the other extreme pregnancies with an interval of >59 months were associated with an increased risk of preterm delivery (OR, 1.20; 95% Cl, 1.17-1.24). (24) Postpartum and preconceptional counseling may help mitigate the risks of pregnancy spacing and decrease rates of preterm delivery.

Maternal stress and depression

Both maternal stress and, to a lesser extent, depression are associated with higher rates of preterm delivery. (6,25-28) Hoffman and colleagues found that the link between maternal stress and preterm delivery is mediated by an increase in maternal cortisol. (26) The investigators prospectively followed 92 low-risk women registering for prenatal care in the first trimester and conducted a battery of psychosocial tests. Women who perceived stress had an increase in both second trimester hair cortisol concentrations (r=0.28, P=.007) and an earlier gestational age at delivery (r=-0.30, P<.01). Maternal depression is also independently associated with an increased risk of preterm delivery. (2,728) One series of more than 7000 women found an increased risk of preterm delivery for depressed women after adjusting for numerous confounders (OR, 1.27; 95% Cl, 1.04-1.55). (27)

Education and socioeconomic status

Education and socioeconomic status are often correlated, and low levels of either have been linked to higher rates of preterm delivery. (29,31) Women with few years of education, regardless of race, are more likely to have a preterm delivery, though racial and ethnic disparities persist even with women who have had at least 16 years of education. (6) Socioeconomically disadvantaged women are also at increased risk for preterm delivery. (6,31) When evaluating the rate of preterm delivery by socioeconomic status, accounting for race, black women who are socioeconomically advantaged continue to have higher rates of preterm delivery compared with equally-advantaged white women, where this advantage decreases the rate of preterm delivery. (32)


Genital tract infections have long been considered risk factors for PTB. (6,17) It is generally believed that these infections are acquired during pregnancy, (6) and studies of treating women presumed to have chronic colonization prior to pregnancy have shown no benefit. (33) Bacterial vaginosis (BV) has consistently been linked to an increased risk of preterm delivery from epidemiologic studies. (34) However, treatment of asymptomatic women with BV did not decrease the rate of preterm delivery in a large, multicenter randomized trial. (35) Further, newer microbiological studies involving molecular techniques are able to identify bacteria in samples with negative traditional cultures. (36,37) However, advanced techniques to identify microbial colonization have also found bacteria present in the amniotic fluid in 70% of women delivering by elective cesarean at term. (38)

The mechanism by which infection leads to preterm delivery is thought to be related to activation of cytokines after micro-organisms are detected by toll-like receptors, initiating the cascade. (17,18) Genetic predisposition for preterm delivery is also linked to infection. Women with a polymorphism of tumor necrosis factor alpha were more likely to have a preterm delivery when bacterial vaginosis was present. (39)

Non-modifiable risk factors


It is well documented that black race carries a higher risk of preterm delivery than any other racial or ethnic group. (6,40,41) Attempts to understand this disparity have adjusted for several confounders including education, socioeconomic status, and other psychosocial issues; yet black women remain at highest risk, even if they are highly educated and in an advantaged socioeconomic class. (42) There are complex factors that may explain this disparity. For instance, it is noted that non-American black women have lower rates of preterm delivery than American black women. (43) A similar phenomenon exists with Hispanic women--named the Hispanic paradox. (41,44) Described primarily among Mexican immigrants, those with similar individual-level risk for preterm delivery including late prenatal care, low socioeconomic status, or low education seemingly have similar rates of PTB to non-Hispanic white women. (44) Interestingly, as a Hispanic woman integrates into society--a phenomenon called acculturation--she is more likely to develop a risk of preterm delivery, similar to a non-Hispanic black woman. (45)


Vaginal bleeding during the first or second trimesters of pregnancy has been consistently associated with an increased risk of PTB. (17,46) This is true whether the bleeding is from a known entity, such as placenta previa or abruption, or whether the bleeding is of unknown origin. (47) One series found a 2- to 3-fold increase in the rate of preterm delivery and a more modest increase in the rate of postpartum hemorrhage for women with an unknown etiology of vaginal bleeding. (47) The exact mechanism relating bleeding to preterm delivery is unclear, but one theory is that decidual hemorrhage leads to thrombin formation, which can initiate a proteolytic casade that results in contractions and preterm premature rupture of the membranes. (18)

Prior PTB

A history of preterm delivery is a major risk factor for recurrent preterm delivery, such that many obstetric preventative interventions have been focused on this cohort. (48,49) The likelihood of recurrence is further modified by the gestational age at the prior delivery and number of prior preterm deliveries; such early and multiple preterm deliveries result in a high rate of recurrence. One series found a 41% rate of recurrent preterm delivery if there were 2 prior preterm deliveries at <34 weeks. (50) Investigators grouped over 19,000 women with 3 consecutive live births to identify the risk of recurrent preterm birth if the first 2 deliveries were very preterm (21-31 weeks' gestation), moderately preterm (32-36 weeks' gestation), or term ([greater than or equal to] 37 weeks' gestation). (51) They found that women who had 2 births at <31 weeks had a 57% rate of recurrent preterm delivery (figure i).


Familial patterns in preterm delivery suggest a genetic predisposition for PTB. Porter and colleagues showed that women who were born preterm are more likely to have preterm deliveries than women born at term (OR, 1.18; 95% Cl, 1.02-1.37). (52) This difference was more marked if the preterm delivery was at <30 weeks' gestation (OR 2.38; 95% Cl, 1.37-4.16). One study identified single-nucleotide polymorphisms in 7 genes associated with spontaneous PTB in black women. (53) Others have described various genetic variants related to preterm delivery in specific subgroups. (39,54,55)

Short cervix

As has been well described in the literature, the shorter the cervical length, the higher the risk of preterm delivery. (56-58) One of the largest studies to document this phenomenon was performed by the Maternal-Fetal Units Medicine Network. (56) In this prospective observational trial, nearly 3000 women had cervical length measurements at 24 and 28 weeks' gestation. The 10th percentile was defined as <25 mm, with a corresponding relative risk of preterm delivery of 6.19 (95% Cl, 3.84-9.97). Cervical length has also been shown to correlate with a risk of preterm delivery as early as 16 weeks, (59) but measurements earlier than that gestational week are not predictive. (60) Cervical funneling has been shown to be highly variable and adds little over cervical length in the prediction of preterm delivery. (61) The most accurate assessment of cervical length is by a transvaginal scan. Whether universal transvaginal cervical length screening should be performed on low-risk women remains controversial, (62,63) but serial endovaginal assessments of the cervix in high-risk women improve the prediction for preterm delivery. (64)


(1.) Martin JA, Hamilton BE, Osterman MJ. Births in the United States, 2013. NCHS Data Brief. 2014(175):1-8.

(2.) Matthews TJ, MacDorman MF, Thoma ME. Infant Mortality Statistics From the 2013 Period Linked Birth/Infant Death Data Set. Natl Vital Stat Rep. 2015;64(9):1-30.

(3.) What are the risk factors for preterm labor and birth? US Department of Health and Human Services. National Institutes of Health. Available at: /conditioninfo/Pages/who_risk.aspx Accessed June 23, 2016.

(4.) Iams JD, Romero R, Culhane JF, Goldenberg RL. Primary, secondary, and tertiary interventions to reduce the morbidity and mortality of preterm birth. Lancet. 2008;371(9607):164-175.

(5.) Hendler I, Goldenberg RL, Mercer BM, et al. The Preterm Prediction Study: association between maternal body mass index and spontaneous and indicated preterm birth. Am J Obstet Gynecol. 2005;192(3):882-886.

(6.) Simhan HN, Berghella V, lams JD. Preterm Labor and Birth. In: Creasy RK Resnik R, lams JD, et al, eds. Creasy & Resnik's Maternal-Fetal Medicine. 7th ed. Philadelphia, Pa: Elsevier; 2014.

(7.) Cnattingius S, Villamor E, Johansson S, et al. Maternal obesity and risk of preterm delivery. JAMA. 2013;309(22):2362-2370.

(8.) Girsen Al, Mayo JA, Carmichael SL, et al. Women's prepregnancy underweight as a risk factor for preterm birth: a retrospective study. BJOG. 2016:doi:10.111/1471-0528.14027.

(9.) Schieve LA, Cogswell ME, Scanlon KS, et al. Prepregnancy body mass index and pregnancy weight gain: associations with preterm delivery. The NMIHS Collaborative Study Group. Obstet Gynecol. 2000;96(2):194-200.

(10.) Scholl TO, Hediger ML, Schall JI, Khoo CS, Fischer RL. Dietary and serum folate: their influence on the outcome of pregnancy. Am J Clin Nutr. 1996;63(4):520-525.

(11.) Kim H, Hwang JY, Kim KN, et al. Relationship between body-mass index and serum folate concentrations in pregnant women. Eur J Clin Nutr. 2012;66(1):136-138.

(12.) Kyrklund-Blomberg NB, Granath F, Cnattingius S. Maternal smoking and causes of very preterm birth. Acta Obstet Gynecol Scand. 2005;84(6):572-577.

(13.) Cnattingius S. The epidemiology of smoking during pregnancy: smoking prevalence, maternal characteristics, and pregnancy outcomes. Nicotine Fob Res. 2004;6 Suppl 2:S125-140.

(14.) Nabet C, Lelong N, Ancel PY, Saurel-Cubizolles MJ, Kaminski M. Smoking during pregnancy according to obstetric complications and parity: results of the EUROPOP study. Eur J Epidemiol. 2007;22(10):715-721.

(15.) Baba S, Wikstrom AK, Stephansson O, Cnattingius S. Influence of smoking and snuff cessation on risk of preterm birth. Eur J Epidemiol. 2012;27(4):297-304.

(16.) Vicedo-Cabrera AM, Schindler C, Radovanovic D, et al. Benefits of smoking bans on preterm and early-term births: a natural experimental design in Switzerland. Tob Control. 2016:doi:10.1136/ tobaccocontrol-2015-052739.

(17.) Goldenberg RL, Culhane JF, lams JD, Romero R. Epidemiology and causes of preterm birth. Lancet. 2008;371(9606):75-84.

(18.) Lockwood CJ, Kuczynski E. Markers of risk for preterm delivery. J Perinat Med. 1999;27(1):5-20.

(19.) Romero R, Espinoza J, Kusanovic JP, et al. The preterm parturition syndrome. BJOG. 2006;113 Suppl 3:17-42.

(20.) Zork N, Biggio J, Tita A, Rouse D, Gyamfi-Bannerman C. Decreasing prematurity in twin gestations: predicaments and possibilities. Obstet Gynecol. 2013;122(2 Pt 1):375-379.

(21.) Evans Ml, Littmann L, King M, Fletcher JC. Multiple gestation: the role of multifetal pregnancy reduction and selective termination. Clin Perinatal. 1992;19(2):345-357.

(22.) Stone J, Belogolovkin V, Matho A, Berkowitz RL, Moshier E, Eddleman K. Evolving trends in 2000 cases of multifetal pregnancy reduction: a single-center experience. Am J Obstet Gynecol. 2007;197(4):394 e391-394.

(23.) Smith GC, Pell JP, Dobbie R. Interpregnancy interval and risk of preterm birth and neonatal death: retrospective cohort study. BMJ. 2003;327(7410):313.

(24.) Conde-Agudelo A, Rosas-Bermudez A, Kafury-Goeta AC. Birth spacing and risk of adverse perinatal outcomes: a meta-analysis. JAMA. 2006:295(15):1809-1823.

(25.) Dole N, Savitz DA, Flertz-Picciotto I, Siega-Riz AM, McMahon MJ, Buekens P. Maternal stress and preterm birth. Am J Epidemiol. 2003:157(1):14-24.

(26.) Floffman MC, Mazzoni SE, Wagner BD, Laudenslager ML, Ross RG. Measures of Maternal Stress and Mood in Relation to Preterm Birth. Obstet Gynecol. 2016;127(3):545-552.

(27.) Venkatesh KK, Riley L, Castro VM, Perlis RH, Kaimal AJ. Association of Antenatal Depression Symptoms and Antidepressant Treatment With Preterm Birth. Obstet Gynecol. 2016:127(5): 926-933.

(28.) Dayan J, Creveuil C, Marks MN, et al. Prenatal depression, prenatal anxiety, and spontaneous preterm birth: a prospective cohort study among women with early and regular care. Psychosom Med. 2006;68(6):938-946.

(29.) Poulsen G, Strandberg-Larsen K, Mortensen L, et al. Exploring educational disparities in risk of preterm delivery: a comparative study of 12 European birth cohorts. Paediatr Perinat Epidemiol. 2015;29(3):172-183.

(30.) Snelgrove JW, Murphy KE. Preterm birth and social inequality: assessing the effects of material and psychosocial disadvantage in a UK birth cohort. Acta Obstet Gynecol Scand. 2015;94(7):766-775.

(31.) Thompson JM, Irgens LM, Rasmussen S, Daltveit AK. Secular trends in socio-economic status and the implications for preterm birth. Paediatr Perinat Epidemiol. 2006;20(3):182-187.

(32.) Braveman PA, Heck K, Egerter S, et al. The role of socioeconomic factors in Black-White disparities in preterm birth. Am J Public Health. 2015;105(4):694-702.

(33.) Tita AT, Cliver SP, Goepfert AR, et al. Clinical trial of interconceptional antibiotics to prevent preterm birth: subgroup analyses and possible adverse antibiotic-microbial interaction. Am J Obstet Gynecol. 2007;197(4):367 e361-366.

(34.) Chaim W, Mazor M, Leiberman JR. The relationship between bacterial vaginosis and preterm birth. A review. Arch Gynecol Obstet. 1997;259(2):51-58.

(35.) Carey JC, Klebanoff MA, Hauth JC, et al. Metronidazole to prevent preterm delivery in pregnant women with asymptomatic bacterial vaginosis. National Institute of Child Health and Human Development Network of Maternal-Fetal Medicine Units. N Engl J Med. 2000;342(8):534-540.

(36.) Yoon BH, Romero R, Lim JH, et al. The clinical significance of detecting Ureaplasma urealyticum by the polymerase chain reaction in the amniotic fluid of patients with preterm labor. Am J Obstet Gynecol. 2003;189(4):919-924.

(37.) Han YW, Shen T, Chung P, Buhimschi IA, Buhimschi CS. Uncultivated bacteria as etiologic agents of intra-amniotic inflammation leading to preterm birth J Clin Microbiol. 2009:47(1):38-47.

(38.) Steel JH, Malatos S, Kennea N, et al. Bacteria and inflammatory cells in fetal membranes do not always cause preterm labor. Pediatr Res. 2005:57(3):404-411.

(39.) Macones GA, Parry S, Elkousy M, Clothier B, Ural SH, Strauss JF, 3rd. A polymorphism in the promoter region of TNF and bacterial vaginosis: preliminary evidence of gene-environment interaction in the etiology of spontaneous preterm birth. Am J Obstet Gynecol. 2004;190(6):1504-1508; discussion 1503A.

(40.) Cunningham FG LK, Bloom SL, Spong CY, Dashe JS, Hoffman BL, Casey BM, Sheffield JS. Williams Obstetrics. 24th edition ed: McGraw-Hill; 2014.

(41.) Culhane JF, Goldenberg RL. Racial disparities in preterm birth. Semin Perinatal. 2011;35(4):234-239.

(42.) Goldenberg RL, Cliver SR Mulvihill FX, et al. Medical, psychosocial, and behavioral risk factors do not explain the increased risk for low birth weight among black women. Am J Obstet Gynecol. 1996;175(5):1317-1324.

(43.) Howard DL, Marshall SS, Kaufman JS, Savitz DA. Variations in low birth weight and preterm delivery among blacks in relation to ancestry and nativity: New York City, 1998-2002. Pediatrics. 2006;118(5):e1399-1405.

(44.) Brown HL, Chireau MV, Jallah Y, Howard D. The "Hispanic paradox": an investigation of racial disparity in pregnancy outcomes at a tertiary care medical center. Am J Obstet Gynecol. 2007;197(2):197 el 91-197; discussion 197 e197-199.

(45.) Ruiz RJ, Saade GR, Brown CE, et al. The effect of acculturation on progesterone/estriol ratios and preterm birth in Hispanics. Obstet Gynecol. 2008;111(2 Pt 1):309-316.

(46.) Yang J, Hartmann KE, Savitz DA, et al. Vaginal bleeding during pregnancy and preterm birth. Am J Epidemiol. 2004:160(2):118-125.

(47.) Bhandari S, Raja EA, Shetty A, Bhattacharya S. Maternal and perinatal consequences of antepartum haemorrhage of unknown origin. BJOG. 2014; 121 (1):44-50; discussion 50-42.

(48.) Spong CY. Prediction and prevention of recurrent spontaneous preterm birth. Obstet Gynecol. 2007;110(2 Pt 1):405-415.

(49.) Mercer BM, Goldenberg RL, Moawad AH, et al. The preterm prediction study: effect of gestational age and cause of preterm birth on subsequent obstetric outcome. National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network. Am J Obstet Gynecol. 1999;181(5 Pt 1): 1216-1221.

(50.) Bloom SL, Yost NP, Mclntire DD, Leveno KJ. Recurrence of preterm birth in singleton and twin pregnancies. Obstet Gynecol. 2001;98(3):379-385.

(51.) McManemyJ, Cooke E, Amon E, Leet T. Recurrence risk for preterm delivery. Am J Obstet Gynecol. 2007;196(6):576 e571-576; discussion 576 e576-577.

(52.) Porter TF, Fraser AM, Hunter CY, Ward RH, Varner MW. The risk of preterm birth across generations. Obstet Gynecol. 1997;90(1):63-67.

(53.) Frey HA, Stout MJ, Pearson LN, et al. Genetic variation associated with preterm birth in African-American women. Am J Obstet Gynecol. 2016.215(2):235e1-8.

(54.) Roberts AK, Monzon-Bordonaba F, Van Deerlin PG, et al. Association of polymorphism within the promoter of the tumor necrosis factor alpha gene with increased risk of preterm premature rupture of the fetal membranes. Am J Obstet Gynecol. 1999, 180(5):1297-1302.

(55.) Gibson CS, MacLennan AH, Dekker GA, et al. Genetic polymorphisms and spontaneous preterm birth. Obstet Gynecol. 2007;109(2 Pt 1):384-391.

(56.) lams JD, Goldenberg RL, Meis PJ, et al. The length of the cervix and the risk of spontaneous premature delivery. National Institute of Child Health and Human Development Maternal Fetal Medicine Unit Network. N Engl J Med. 1996;334(9):567-572.

(57.) Andersen HF, Nugent CE, Wanty SD, Hayashi RH. Prediction of risk for preterm delivery by ultrasonographic measurement of cervical length. Am J Obstet Gynecol. 1990;163(3):859-867.

(58.) Hartmann K, Thorp JM, Jr., McDonald TL, Savitz DA, Granados JL. Cervical dimensions and risk of preterm birth: a prospective cohort study. Obstet Gynecol. 1999;93(4):504-509.

(59.) Hibbard JU, Tart M, Moawad AH. Cervical length at 16-22 weeks' gestation and risk for preterm delivery. Obstet Gynecol. 2000;96(6):972-978.

(60.) Conoscenti G, Meir YJ, D'Ottavio G, et al. Does cervical length at 13-15 weeks' gestation predict preterm delivery in an unselected population? Ultrasound Obstet Gynecol. 2003;21(2):128-134.

(61.) Berghella V, Owen J, MacPherson C, et al. Natural history of cervical funneling in women at high risk for spontaneous preterm birth. Obstet Gynecol. 2007;109(4):863-869.

(62.) Jain S, Kilgore M, Edwards RK, Owen J. Revisiting the cost-effectiveness of universal cervical length screening: importance of progesterone efficacy. Am J Obstet Gynecol. 2016.

(63.) Khalifeh A, Berghella V. Universal cervical length screening in singleton gestations without a previous preterm birth: ten reasons why it should be implemented. Am J Obstet Gynecol. 2016;214(5):603 e601-605.

(64.) Owen J, Yost N, Berghella V, et al. Mid-trimester endovaginal sonography in women at high risk for spontaneous preterm birth. JAMA. 2001;286(11):1340-1348.

Cynthia Gyamfi-Bannerman, MD, MSc, has nothing to disclose.

Cynthia Gyamfi-Bannerman, MD, MSc

Ellen Jacobson Levine and Eugene Jacobson Associate Professor of Women's Health In OBGYN

Department of Obstetrics and Gynecology

Division of Maternal-Fetal Medicine

Columbia University Medical Center

New York, NY
TABLE 1 Risk factors for preterm delivery

Modifiable        Potentially modifiable     Non-modifiable

Low BMI/obesity   Short or prolonged         Black race
                  interpregnancy interval
Smoking           Maternal stress/           Genetics

                  (Higher order) multiple    Prior preterm birth

                  Education and              Short cervix
                  socioeconomic status

                  Infection/inflammation     First or second
                                             trimester vaginal

Abbreviation: BMI, body mass index.

FIGURE 1 Recurrence of preterm birth by gestational
age and number of preterm deliveries (51)

Preterm delivery risk (%)

Very/Very             57
Moderate/Very         50
Very/Moderate         40
Moderate/Moderate     38

Term/Very             23
Term/Moderate         21

Term/Very             15
Term Moderate         12

Term/Term              5

Preterm delivery risk based on outcomes from prior 2 pregnancies.
Very preterm (21-31 weeks' gestation), Moderately preterm (32- 36
weeks' gestation), Term ([greater than or equal to] 37 weeks'

Reprinted from Am J Obstet Gynecol, 196(6), McManemy J, Cooke E,
Amon E, Leet T, Recurrence risk for preterm delivery, e571-576,
2007, with permission from Elsevier.
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Date:Sep 1, 2016
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