Obstetrician & Gynecologist (OB/GYN)
17 years of experience
Video profile
Accepting new patients

Education ?

Medical School Score Rankings
Emory University (1993)
  • Currently 4 of 4 apples
Top 25%

Awards & Distinctions ?

Medical College of Georgia School of Medicine
American Board of Obstetrics and Gynecology

Affiliations ?

Dr. Yost is affiliated with 19 hospitals.

Hospital Affilations



  • Medical City Dallas Hospital
    7777 Forest Ln, Dallas, TX 75230
    • Currently 4 of 4 crosses
    Top 25%
  • UT Southwestern University Hospital - Zale Lipshy
    5151 Harry Hines Blvd, Dallas, TX 75235
    • Currently 4 of 4 crosses
    Top 25%
  • Baylor Medical Center At Garland
    2300 Marie Curie Dr, Garland, TX 75042
    • Currently 3 of 4 crosses
    Top 50%
  • Doctors Hospital Dallas
  • Longview Regional Medical Center
  • Baylor University Medical Center
  • Mcg Health, Inc
  • St Paul Hospital
  • Parkland Health & Hospital System
  • Good Shepard
  • Good Shepherd Medical Center
  • UT Southwestern Zale Lipshy Hospital
  • Parkland Hospital
  • Children S Hospital
  • Baylor Hospital
  • Grady Health Systems
  • University Hospital - St Paul
  • Children's Medical Center of Dallas
  • Medical City
  • Publications & Research

    Dr. Yost has contributed to 16 publications.
    Title Estrogen and Progesterone Metabolism in the Cervix During Pregnancy and Parturition.
    Date July 2008
    Journal The Journal of Clinical Endocrinology and Metabolism

    CONTEXT: Experimental and clinical studies in a variety of nonprimate species demonstrate that progesterone withdrawal leads to changes in gene expression that initiate parturition at term. Mice deficient in 5alpha-reductase type I fail to undergo cervical ripening at term despite the timely onset of luteolysis and progesterone withdrawal in blood. OBJECTIVE: Our objective was to test the hypothesis that estrogen and progesterone metabolism is regulated in cervical tissues during pregnancy, even in species in which parturition is not characterized by progesterone withdrawal in blood. DESIGN: Estradiol and progesterone metabolism was quantified in intact cervical tissues from nonpregnant and pregnant women at term before or after labor. SETTING: The study was conducted at a university hospital. PATIENTS: Tissues were obtained from five nonpregnant and 21 pregnant women (nine before labor and 12 in labor). MAIN OUTCOME MEASURES: Enzyme activity measurements, Northern blot analysis, quantitative real-time RT-PCR, and immunohistochemistry were used to quantify steroid hormone metabolizing enzymes in cervical and myometrial tissues. RESULTS: During pregnancy, 17beta-hydroxysteroid dehydrogenase type 2 was induced in glandular epithelial cells to catalyze the conversion of estradiol to estrone and stroma-derived 20alpha-hydroxyprogesterone to progesterone. During parturition, 17beta-hydroxysteroid dehydrogenase type 2 was down-regulated in endocervical cells, thereby creating a microenvironment favorable for cervical ripening. CONCLUSIONS: Together, the data indicate that cervical ripening during parturition involves localized regulation of estrogen and progesterone metabolism through a complex relationship between cervical epithelium and stroma, and that steroid hormone metabolism in cervical tissues from pregnant women is unique from that in mice.

    Title Magnetic Resonance Signal Characteristics of the Cervix As Pregnancy Advances.
    Date December 2007
    Journal Reproductive Sciences (thousand Oaks, Calif.)

    The objective of this study is to describe magnetic resonance (MR) signal intensity (SI) changes in the cervix during pregnancy. This is an observational cohort study of women with a history of preterm delivery. MR imaging sequences were performed every 3 to 4 weeks. Using 8 regions of interest, the SIs are quantified and analyzed with respect to gestational age. Twenty-seven MR studies were performed on a cohort of 8 women. The SIs of the external os are significantly greater than those of the internal os ( P = .035). Similarly, the SIs of the outer stroma are greater than those of the inner stroma (P = .002). As gestational age advances, the inner to outer stromal SI ratio increases, primarily because of a decreasing SI in the outer stromal layer (P = .03). The MR SIs of the cervical stromal zones display variability during pregnancy and decrease with advancing gestation.

    Title Effect of Coitus on Recurrent Preterm Birth.
    Date May 2006
    Journal Obstetrics and Gynecology

    OBJECTIVE: To estimate the impact of sexual behavior on the risk of recurrent spontaneous preterm birth at less than 37 weeks of gestation. METHODS: This is a secondary analysis of a multicenter, blinded observational study of endovaginal sonographic examinations performed at 16-18 weeks of gestation on 187 women with singleton gestations who were at high risk for recurrent spontaneous preterm birth (prior spontaneous preterm birth at < 32 weeks of gestation). At the time of enrollment, each woman was interviewed by a research nurse with regard to her sexual history. The patient was asked about the number of sexual partners in her lifetime, the number of sexual partners since the start of her pregnancy, and, on average, the frequency of intercourse per week in the preceding month. RESULTS: A total of 165 pregnancies were available for this analysis. The population incidence of spontaneous preterm birth at less than 37 weeks of gestation in the study pregnancy was 36%. An increasing number of sexual partners in a woman's lifetime was associated with an increased risk of spontaneous preterm delivery (one partner 19%, 2-3 partners 29%, >or= 4 partners 44%, P = .007), whereas the number of sexual partners since the start of pregnancy was not (P = .42). Women who reported infrequent sexual intercourse during early pregnancy had an incidence of recurrent spontaneous preterm birth of 28% compared with 38% in those women who reported some intercourse (P = .35). CONCLUSION: Self-reported coitus during early pregnancy was not associated with an increased risk of recurrent preterm delivery. There was an association between increasing number of sexual partners in a woman's lifetime and recurrent preterm delivery. LEVEL OF EVIDENCE: II-2.

    Title Hospitalization for Women with Arrested Preterm Labor: a Randomized Trial.
    Date August 2005
    Journal Obstetrics and Gynecology

    OBJECTIVE: To determine whether hospitalization of women with arrested preterm labor has an effect on delivery at 36 weeks or greater when compared with women discharged home. METHODS: All women with a singleton gestation and a diagnosis of arrested preterm labor with intact membranes between 24 and 33 weeks, 4 days of gestation were randomly assigned to home or hospital management. Upon completion of a dexamethasone course, women assigned to outpatient management were promptly discharged, and women in the inpatient group were advised to continue hospitalization until 34 weeks. Decreased activity was encouraged in both groups. Bed rest was not strictly enforced. The primary outcome was delivery at 36 weeks or greater. RESULTS: A total of 101 women of a planned 188 were enrolled at the time of an interim analysis. There was no difference in the primary study outcome between the 2 groups and the trial was terminated. Among the hospitalized women, 71% reached 36 weeks or greater, compared with 72% of those discharged home (P = .89). The mean cervical dilatation in hospitalized women was 2.7 +/- 0.5 cm, compared with 2.6 +/- 0.5 cm in women discharged home (P = .16). The overall length of hospital stay for the women allocated to hospitalization was 16 +/- 13 days. CONCLUSION: Compared with hospitalization, outpatient management of women with arrested preterm labor and intact membranes had no effect on the rate of preterm birth. LEVEL OF EVIDENCE: I.

    Title A Prospective Observational Study of Domestic Violence During Pregnancy.
    Date August 2005
    Journal Obstetrics and Gynecology

    OBJECTIVE: To assess whether women reporting domestic violence are at increased risk for adverse pregnancy outcomes. METHODS: A screening questionnaire, previously validated for the identification of female victims of domestic violence, was offered to women presenting to our Labor and Delivery Unit. The survey prompted women to indicate whether her partner or family member physically hurt her, insulted or talked down to her, threatened her with harm, or screamed or cursed at her. The primary study outcome was to detect a 3-fold increase in low birth weight infants (< or = 2,500 g) in women reporting physical abuse, compared with those not reporting domestic violence. RESULTS: A total of 16,041 women were approached to be interviewed. Of these, 949 (6%) women responded affirmatively to one or more of the survey questions, and another 94 (0.6%) declined to be interviewed. The incidence of low birth weight infants was significantly increased in women who reported verbal abuse, compared with the no-abuse group (7.6% versus 5.1%, respectively, P = .002). Physical abuse was associated with an increased risk of neonatal death (1.5% versus 0.2%, P = .004). Interestingly, women who declined to be interviewed had significantly increased rates of low birth weight infants (12.8% versus 5.1%, P < .001), preterm birth at 32 weeks of gestation or less (5.3% versus 1.2%, P = .002), placental abruptions (2.1% versus 0.2%, P < .001), and neonatal intensive care admissions (7.4% versus 2.2%, P = .008) when compared with women in the no-abuse group, respectively. CONCLUSION: Women who declined to be surveyed regarding domestic violence were at increased risk for adverse pregnancy outcome. LEVEL OF EVIDENCE: II-2.

    Title Number and Gestational Age of Prior Preterm Births Does Not Modify the Predictive Value of a Short Cervix.
    Date September 2004
    Journal American Journal of Obstetrics and Gynecology

    OBJECTIVE: This study was undertaken to determine whether the number and gestational age of prior preterm deliveries modifies the significance of endovaginal sonographic cervical length less than 25 mm for the prediction of recurrent preterm birth less than 35 weeks' gestation. STUDY DESIGN: Secondary analysis of a multicenter, blinded, observational study. Endovaginal ultrasonographic examinations were scheduled at 2-week intervals between 16 and 23 weeks' gestation in singleton pregnancies of 181 gravid women with at least 1 prior spontaneous preterm birth between 16 and 32 weeks' gestation. RESULTS: The earliest prior preterm birth occurred before 23 weeks in 61 women and at 23.0 to 31 weeks in 115; 5 had missing gestational age data. Cervical length was not different between these 2 groups both at the initial scan (median 38 vs 37 mm, P=.54) and considering the shortest ever observed cervical length over the entire study period (median 30 vs 30 mm, P=.97). Cervical length less than 25 mm was associated with spontaneous preterm birth less than 35 weeks for both groups (positive predictive value 80% vs 71%, P>.99). There were 134 women with 1 prior preterm delivery (74%) and 47 with 2 or more. Cervical lengths were not different between these 2 groups at the initial scan (median 36.5 vs 37 mm, P=.52) or over the entire study period (median 30 vs 32 mm, P=.31). The positive predictive value of cervical length less than 25 mm for subsequent spontaneous premature birth was not significantly higher in gravid women with multiple prior preterm births (100% vs 73%, P>.99). CONCLUSION: Neither the number nor the gestational age of prior preterm births modify the predictive value of a cervical length less than 25 mm at 16 to 19 weeks for recurrent spontaneous preterm birth.

    Title A Hospital-sponsored Quality Improvement Study of Pain Management After Cesarean Delivery.
    Date July 2004
    Journal American Journal of Obstetrics and Gynecology

    OBJECTIVE: We undertook this study to systematically assess prevailing pain management regimes used at our hospital in women after cesarean delivery. STUDY DESIGN: Between August 1999 and July 2000, all women delivered by cesarean section at Parkland Hospital were assigned to 1 of 4 different pain management strategies: (1). intramuscular (IM) meperidine, (2). patient-controlled analgesia (PCA) meperidine, (3). IM morphine sulfate, and (4). PCA morphine sulfate. A combination of methods were used to compare these different pain management strategies. A survey questionnaire, using Likert scale responses, was administered to evaluate maternal satisfaction with pain control. Visual Analog Scale (VAS) scores and information regarding breastfeeding and rooming-in were also collected. RESULTS: A total of 1256 women were allocated to the 4 analgesia study groups. The median meperidine dosages for the IM and PCA groups were 350 mg and 600 mg, respectively (P <or=.01). Conversely, the median IM morphine dose (65 mg) was significantly higher than that for the PCA group (60 mg). The percentage of women reporting moderate or worse pain (VAS scores 4 or more) was significantly lower in those women who received PCA meperidine compared with IM meperidine. Women who received morphine reported less severe pain compared with meperidine, regardless of route of administration. The patients' subjective report of satisfaction with pain management was not related to the method or drug used for pain control (P=.13). Fewer women assigned to morphine therapy stopped breastfeeding (P=.02) and more roomed-in with their infants (P <.01). CONCLUSION: Pain relief was superior with the morphine regimens used and was positively associated with breastfeeding and infant rooming-in.

    Title Second-trimester Cervical Sonography: Features Other Than Cervical Length to Predict Spontaneous Preterm Birth.
    Date April 2004
    Journal Obstetrics and Gynecology

    OBJECTIVE: To estimate whether cervical and lower uterine segment characteristics other than cervical length and funneling predict recurrent preterm birth. METHODS: We conducted a secondary analysis of a multicenter, blinded observational study of 181 women with singletons and prior spontaneous preterm births. Endovaginal ultrasonic examinations were performed at 2-week intervals between 16 0/7 weeks and 23 6/7 weeks of gestation. Cervical canal contour (straight/curved), cervical position (horizontal/vertical), posterior cervical width, lower uterine segment thickness, vascularity, endocervical canal dilation, with or without associated membrane prolapse and chorioamnion visible at the internal os, were systematically assessed. RESULTS: At the initial sonogram (16 0/7-18 6/7 weeks), membranes visible overlying the internal os (relative risk 1.9, confidence interval [CI] 1.2, 3.1) and canal dilation of 2-4 mm (relative risk 2.6, CI 1.4, 4.7) were significant predictors of spontaneous preterm birth of less than 35 weeks in univariate analyses. Only canal dilation remained statistically significant after controlling for cervical length (odds ratio 5.5, CI 1.1, 28.6). CONCLUSION: Endocervical canal dilation of 2-4 mm during second-trimester endovaginal sonography was associated with an increased risk of recurrent preterm delivery independent of cervical length. LEVEL OF EVIDENCE: II-2

    Title Critical Care Infectious Disease.
    Date February 2004
    Journal Obstetrics and Gynecology Clinics of North America

    Septic shock, toxic shock syndrome, acute respiratory distress syndrome, and catheter-related infections are conditions in which intensive care management of the patient may be necessary. Toxic shock syndrome is a toxin-mediated illness that is not limited to young menstruating women and should be considered in women and men who present with fever, hypotension, rash, and multiorgan dysfunction. Sepsis is the leading cause of death in critically ill patients in the United States and is the most common predisposing factor for acute lung injury or acute respiratory distress syndrome. Central venous catheters are often a necessity for optimal patient care in these critically ill patients.

    Title A Randomized, Placebo-controlled Trial of Corticosteroids for Hyperemesis Due to Pregnancy.
    Date January 2004
    Journal Obstetrics and Gynecology

    OBJECTIVE: Hyperemesis gravidarum, a severe form of nausea and vomiting due to pregnancy for which there is no proven pharmacological treatment, is the third leading cause for hospitalization during pregnancy. Corticosteroids are commonly used for the treatment of nausea and vomiting due to cancer chemotherapy-induced emesis and might prove useful in hyperemesis gravidarum. METHODS: A randomized, double-blind, placebo-controlled trial was conducted in 126 women who previously had not responded to outpatient therapy for hyperemesis gravidarum during the first half of pregnancy. Intravenous methylprednisolone (125 mg) was followed by an oral prednisone taper (40 mg for 1 day, 20 mg for 3 days, 10 mg for 3 days, 5 mg for 7 days) versus an identical-appearing placebo regimen. All women also received promethazine 25 mg and metoclopramide 10 mg intravenously every 6 hours for 24 hours, followed by the same regimen administered orally as needed until discharge. The primary study outcome was the number of women requiring rehospitalization for hyperemesis gravidarum. RESULTS: A total of 110 women delivered at our hospital and had pregnancy outcomes available for analysis; 56 were randomized to corticosteroids and 54 were administered placebo. Nineteen women in each study group required rehospitalization (34% versus 35%, P =.89, for corticosteroids versus placebo, respectively). CONCLUSION: The addition of parenteral and oral corticosteroids to the treatment of women with hyperemesis gravidarum did not reduce the need for rehospitalization later in pregnancy.

    Title Acute Renal Failure in Association with Severe Hyperemesis Gravidarum.
    Date November 2002
    Journal Obstetrics and Gynecology

    BACKGROUND: Severe hyperemesis gravidarum is a rare but potentially devastating complication of pregnancy. Among its many potential complications are dehydration, electrolyte imbalance, malnutrition, Wernicke encephalopathy, and compromised renal function. CASE: We report the case of a 21-year-old woman at 15 weeks' gestation presenting to the emergency department with severe hyperemesis gravidarum associated with acute renal failure. Her initial serum creatinine and blood urea nitrogen were 10.7 mg/dL and 171 mg/dL, respectively. The patient underwent daily hemodialysis for 5 days with subsequent return of renal function to normal. CONCLUSION: Women with severe hyperemesis gravidarum may be at risk for acute renal failure caused by severe intravascular volume depletion.

    Title Recurrence of Preterm Birth in Singleton and Twin Pregnancies.
    Date September 2001
    Journal Obstetrics and Gynecology

    OBJECTIVE: To assess recurrence of preterm birth and its impact on an obstetric population. METHODS: Women with consecutive births at our hospital beginning with their first pregnancy were identified (n = 15,945). The first pregnancy was categorized as delivered between 24 and 34 weeks' gestation or 35 weeks or beyond, singleton or twin, and spontaneous or induced. The risk of preterm delivery in these same women during subsequent pregnancies was then analyzed. RESULTS: Compared with women who delivered a singleton at or beyond 35 weeks' gestation in their first pregnancy, those who delivered a singleton before 35 weeks were at a significant increased risk for recurrence (odds ratio [OR] 5.6, 95% confidence interval [CI] 4.5, 7.0), whereas those who delivered twins were not (OR 1.9, 95% CI 0.46, 8.14). The OR for recurrent spontaneous preterm birth presenting with intact membranes was 7.9 (95% CI 5.6, 11.3) compared with 5.5 (95% CI 3.2, 9.4) with ruptured membranes. Of those women with a recurrent preterm birth, 49% delivered within 1 week of the gestational age of their first delivery and 70% delivered within 2 weeks. Among 15,863 nulliparous women with singleton births at their first delivery, a history of preterm birth in that pregnancy could predict only 10% of the preterm births that ultimately occurred in the entire obstetric population. CONCLUSION: In a population-based study at our hospital, women who initially delivered preterm and thus were identified to be at risk for recurrence ultimately accounted for only 10% of the prematurity problem in the cohort.

    Title Infection and Preterm Labor.
    Date May 2001
    Journal Clinical Obstetrics and Gynecology

    There are many conditions, such as non-white race, young maternal age, and uterine malformations, that have been associated with preterm birth that are not amenable to intervention. Maternal cervical and intrauterine infection and inflammation may have a primary causative role in a fraction of the cases of preterm birth and preterm rupture of membranes and may also interact adversely with a variety of maternal (shortened cervix, smoking) and fetal factors (polyhydramnios, multifetal gestation) to decrease the threshold to preterm birth. Further studies are needed to better-define the link between various maternal microbial colonizations and preterm delivery, with the possibility to establish new screening and treatment recommendations. Because of the innumerable causes of preterm birth, a new strategy of targeted treatment of cervical or vaginal infections may lead to only a modest reduction in the incidence of this devastating problem of modern obstetrics.

    Title An Appraisal of Treatment Guidelines for Antepartum Community-acquired Pneumonia.
    Date August 2000
    Journal American Journal of Obstetrics and Gynecology

    OBJECTIVE: The optimal strategy for the initial evaluation and management, including criteria for hospitalization, of pregnant women with pneumonia has not been defined. Our purpose was to evaluate a treatment protocol for antepartum pneumonia and to identify criteria for selection of women for potential outpatient treatment. STUDY DESIGN: A protocol based on British and American Thoracic Society guidelines was introduced and included prompt hospitalization and empiric initiation of erythromycin therapy. Maternal and neonatal outcomes were analyzed to assess the efficacy of the protocol. A second analysis involved the retrospective application of published guidelines to ascertain for which women outpatient management might have been appropriate. RESULTS: There were no maternal deaths among the 133 women studied, and in 14 (10%) women there was a misdiagnosis at admission. Erythromycin monotherapy was judged adequate in all but one of the 99 women so treated. Using a modified version of the American Thoracic Society guidelines, we project that only 25% of the women hospitalized with pneumonia could have been managed safely as outpatients. CONCLUSION: Most pregnant women with pneumonia respond well to monotherapy with erythromycin. Outpatient management may be a reasonable option for selected women.

    Title Pitfalls in Ultrasonic Cervical Length Measurement for Predicting Preterm Birth.
    Date May 1999
    Journal Obstetrics and Gynecology

    OBJECTIVE: To describe the anatomic and technical difficulties encountered with transvaginal ultrasound imaging of the cervix in a consecutive series of women at risk for preterm delivery. METHODS: Three groups of women had cervical ultrasound examinations: those with histories of preterm birth, those with incompetent cervices, and those admitted for preterm labor that did not progress. Standardized ultrasound examinations of the cervix involved measuring the length of the endocervical canal, funneling length, and internal os dilation with and without fundal pressure. RESULTS: Sixty consecutive women had transvaginal ultrasound examinations for assessment of the cervix. Forty-six had histories of preterm birth, five had incompetent cervices, and nine had arrested preterm labor. Six types of problems arose, which can be divided into anatomic or technical considerations, with an overall frequency of 27% (95% confidence interval 16%, 40%). Anatomic pitfalls that hampered identification of the internal os included an undeveloped lower uterine segment (n = 5), a focal myometrial contraction (n = 1), rapid and spontaneous cervical change (n = 1), and an endocervical polyp (n = 1). Technical pitfalls included incorrect interpretation of internal os dilation because of vaginal probe orientation (n = 7) and artificial lengthening of the endocervical canal because of distortion of the cervix by the transducer (n = 1). CONCLUSION: We caution those who perform cervical length examinations to be wary of falsely reassuring findings due to potential anatomic and technical pitfalls.

    Title Postpartum Regression Rates of Antepartum Cervical Intraepithelial Neoplasia Ii and Iii Lesions.
    Date April 1999
    Journal Obstetrics and Gynecology

    OBJECTIVE: To study the histologic regression and progression rates of cervical intraepithelial neoplasia (CIN) II and III after delivery and the effect the route of delivery has on the regression rates of CIN. METHODS: Pregnant patients with satisfactory colposcopic examinations and biopsy-proven CIN II and III were identified. Delivery information and postpartum biopsy results were obtained by chart review. RESULTS: Two hundred seventy-nine patients had antepartum biopsies of CIN II or CIN III. Of these, 126 women were excluded for the following reasons: lost to follow-up (75), human immunodeficiency virus positive (two), cesarean hysterectomy (four), and inadequate postpartum follow-up (45). This yielded a study group of 153 patients consisting of 82 with CIN II and 71 with CIN III. The regression rates were 68% and 70% among CIN II and CIN III patients (P = .78), respectively. Seven percent of patients with CIN II progressed to CIN III on postpartum evaluation. Twenty-five percent of those patients with CIN II and 30% of those with CIN III remained the same postpartum. No CIN lesions progressed to invasive carcinoma. There were no differences in regression rates or progression rates among the women who had vaginal deliveries (130), women who labored and then underwent cesarean (17), or women who proceeded to a cesarean without laboring (six). CONCLUSION: We found similar high postpartum regression rates despite the route of delivery. We recommend conservative antepartum management with postpartum colposcopic evaluation regardless of route of delivery because we are unable to predict which of these lesions are more likely to regress.

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