Is the Relationship between Short Interpregnancy Interval and Preterm Birth Related to a Short Cervix?

Objective Our objective was to determine if the relationship between interpregnancy interval (IPI) and preterm delivery was related to cervical shortening. Methods This is a secondary analysis of a prospective cohort study designed to assess the relationship between cervical length (CL) and preterm delivery. Multiparous patients, who had transvaginal CLs obtained at 22 to 24 weeks and complete pregnancy outcome data available were included. The women were divided into two groups: Group 1 with an IPI of ≤ 1 year and Group 2 with an IPI of > 1 year. The primary outcome was short cervix (CL < 2.5 cm) at 24 weeks. The secondary outcome was the incidence of preterm delivery < 37 weeks. Interaction between short cervix and IPI was examined in a regression model. Results There were 155 women in Group 1 and 328 women in Group 2. There was no difference in the incidence of short cervix between groups (10.0% in Group 1 and 12.9% in Group 2, p = 0.35). In a logistic regression model, short IPI and short cervix were independently associated with preterm birth. Conclusion The relationship between short IPI and preterm birth is not explained by a short cervix. They remain independent risk factors for preterm birth.

Investigating the mechanical function of the cervix during pregnancy using finite element models derived from high-resolution 3D MRI.

Preterm birth is a strong contributor to perinatal mortality, and preterm infants that survive are at risk for long-term morbidities. During most of pregnancy, appropriate mechanical function of the cervix is required to maintain the developing fetus in utero. Premature cervical softening and subsequent cervical shortening are hypothesized to cause preterm birth. Presently, there is a lack of understanding of the structural and material factors that influence the mechanical function of the cervix during pregnancy. In this study we build finite element models of the pregnant uterus, cervix, and fetal membrane based on magnetic resonance imagining data in order to examine the mechanical function of the cervix under the physiologic loading conditions of pregnancy. We calculate the mechanical loading state of the cervix for two pregnant patients: 22 weeks gestational age with a normal cervical length and 28 weeks with a short cervix. We investigate the influence of (1) anatomical geometry, (2) cervical material properties, and (3) fetal membrane material properties, including its adhesion properties, on the mechanical loading state of the cervix under physiologically relevant intrauterine pressures. Our study demonstrates that membrane-uterus interaction, cervical material modeling, and membrane mechanical properties are factors that must be deliberately and carefully handled in order to construct a high quality mechanical simulation of pregnancy.

Effect of cervical cerclage on rate of cervical shortening.

OBJECTIVE: Although cerclage has been shown to reduce the risk of recurrent preterm birth in a high-risk patient population, the mechanism by which this occurs is not well understood. Our objective was to evaluate whether cerclage affects the rate of cervical shortening taking into account exposure to 17-hydroxyprogesterone and vaginal progesterone. METHODS: This was a retrospective cohort study of women who had serial cervical length measurements due to a history of spontaneous preterm delivery. Demographic data, obstetric history, progesterone administration, delivery information and serial cervical length measurements were collected. The rate of cervical shortening was compared in women with and without cerclage. Subgroup analyses were performed to compare rates of cervical shortening by indication for cerclage (history indicated vs ultrasound indicated) and outcome in the current pregnancy (cerclage vs no cerclage among those who delivered preterm). RESULTS: A total of 414 women were included of whom 32.4% (n = 134) had a cerclage. There was no difference in the rate of cervical shortening between the cerclage (0.8 mm/week) and no-cerclage (1.0 mm/week, P = 0.43) groups. The rates of cervical shortening among history-indicated and ultrasound-indicated cerclage groups were similar (0.9 vs 1.3 mm/week, respectively, P = 0.2). Among patients with a preterm delivery in the index pregnancy, the rates of cervical shortening among those with (1.31 mm/week) and without (1.28 mm/week, P = 0.78) cerclage were also similar. CONCLUSION: Cervical shortening among women with cerclage occurs at a similar rate to that among women without a cerclage, regardless of indication for cerclage or pregnancy outcome.

Vaginal progesterone in women with twin gestations complicated by short cervix: a retrospective cohort study.

OBJECTIVE: To determine whether the use of vaginal progesterone in twin gestations with a cervical length (CL) of ≤2.5 cm is associated with a reduced risk of preterm delivery. DESIGN: Retrospective cohort study. SETTING: Tertiary-care medical centre in New York City. POPULATION: Women with twin gestations undergoing sonographic cervical length screening. METHODS: Women with twin gestations with a CL of ≤2.5 cm between 16 and 32 weeks of gestation, and who delivered at our centre between 2010 and 2013, were included. We evaluated the impact of vaginal progesterone on the risk of preterm delivery using a Cox proportional hazard model, adjusted for potential confounding factors. We then performed a propensity score analysis using inverse probability of treatment weights to account for treatment selection bias and confounding. MAIN OUTCOME MEASURE: Delivery prior to 35 weeks of gestation. RESULTS: Of the 167 twin pregnancies analysed, 61 (35.7%) were treated with vaginal progesterone. The hazard ratio (HR) of delivery prior to 35 weeks of gestation in the vaginal progesterone group, compared with the no vaginal progesterone group, was 1.8 (95% confidence interval, 95% CI 1.5-3.1) in the unadjusted analysis, 1.4 (95% CI 0.7-3.2) following multivariable adjustment for confounding factors, and 1.5 (95% CI 1.1-2.3) using propensity score methods. CONCLUSION: Women with more risk factors for preterm delivery were more likely to be treated with vaginal progesterone. After statistically correcting for this with propensity score methods, we found that vaginal progesterone therapy in twin pregnancies with a CL ≤2.5 cm was associated with an increased risk of preterm delivery.

Predicting fetal karyotype in fetuses with omphalocele: The current role of ultrasound.

OBJECTIVE: To assess the ability of ultrasound in predicting abnormal karyotype in pregnancies with prenatally diagnosed omphaloceles and to compare its test characteristics to previously published studies. METHODS: A retrospective case-control study of omphaloceles diagnosed at one center was performed from 1995-2007. Cases were those with an abnormal karyotype and controls were those with a normal karyotype. Data collection included demographics, karyotype results, and ultrasound findings. The number and type of associated anomalies were compared between the cases and controls. The sensitivity, specificity, positive predictive value, and negative predictive value for predicting an abnormal karyotype were calculated from previously published studies. RESULTS: Of the 73 subjects, there were 12 cases and 61 controls. The majority of women were Caucasian and primigravida. The cases were less likely to have an isolated omphalocele [1 (8.3%) vs. 27 (42.6%), OR = 0.122; 95% CI: 0.02-0.08] but were more likely to have two or more major anomalies [8 (66.7%) vs. 17 (27.9%), OR = 5.18; 95% CI: 1.19-24.04)] compared to the controls. Cardiac anomalies and only one additional major anomaly were not different between the two groups, P > 0.05. The test characteristics for this study were similar to previously published studies. CONCLUSIONS: Isolated omphaloceles were more likely to have a normal karyotype; however fetuses with multiple anomalies were more likely to have an abnormal karyotype. Despite advances in ultrasound technology, its ability for predicting an abnormal karyotype in these fetuses has not improved.