Please select the eligibility criteria that correspond to the clinical trial below.
Title: "Comparison of Vaginal Progesterone With Arabin Cervical Pessary and Vaginal Progesterone Alone in the Prevention of Preterm Delivery in Singleton Pregnancies With Incidental Premature Shortening of Cervical Length"
Brief Summary: 1. This will be a randomized prospective and open-label study with no placebo control or blinding of the participants and the research team members. The study is to compare the effectiveness of vaginal progesterone versus combination of vaginal progesterone and Arabin cervical pessary in the prevention of preterm delivery among patients with incidental shortened cervical length.
2. As part of standard clinical care, all pregnant patients usually have cervical length measurements at the mid-trimester during the anatomy scan from 18 to 24 weeks with the GE ultrasound Volusion 8 using the vaginal probe.

   1. Patients with short cervix will be counseled and offered the opportunity to participate in the study.
   2. All participants will be taught how to use the vaginal progesterone once daily prior to bedtime. In addition, those in the combination group will have the cervical pessary placed in the clinic right away or within a week if they request for more time to brood over their diagnosis and weigh on the option of inserting Arabin pessary.
   3. All participants will be followed up in the high-risk obstetric clinic as per standard prenatal care. Frequency of follow up visits will be individualized depending on patient's need and comorbidities. , Participants will be requested to bring the remnant of the vaginal progesterone to the clinic to assess compliance.
   4. Participants in the study will continue their prenatal care with UIC high-risk obstetric clinic until delivery.
   5. The study recruitment will occur for a period of 2 years starting from November 2016 to October 2018 or until all the anticipated numbers of study subjects have been attained.
   6. There will be 10 % over-sampling to cater for those who will drop out from the study or loss to follow up after randomization, and those who delivered in another hospital.
   7. Participants will have access to one of the investigators or the high- risk clinic nurse for any complaints related to their conditions.
   8. Participants can opt out at any stage of the study if they do not want to continue further or if there are any adverse effects.


Options:
A: Inclusion Criteria:

* patient with a short cervix equal to or less than 25 mm by transvaginal ultrasound
* gestational age between 18 (0/7) and 23 (6/7) weeks of gestation according to the results of the ultrasound of the first trimester, or by integrating the date of the last period
* patients who were informed of the study and agreed to sign the consent form.

Exclusion Criteria:

* pregnancy with a fetus with a major congenital malformation - regular and painful uterine activity - history of preterm premature rupture of membranes (PPROM) - active vaginal bleeding - complete and incomplete placenta previa - cerclage of the cervix in place - antecedent of conisation - multiple gestation - ballooning of membranes outside the cervix into the vagina - allergy/intolerance or hypersensitivity to progesterone or any of its ingredients - chronic medical conditions that would interfere with study participation or evaluation of treatment - vaginal administration of another drug.
B: Inclusion Criteria:

* Women with a singleton pregnancy and a history of at least one previous preterm delivery before 34+0 weeks and/or a history of at least one previous cervical surgery
* 12+0 - 16+0 weeks of gestation at time of randomization
* only women with minimum age of 18 and capable of giving consent

Exclusion Criteria:

* major fetal abnormalities
* uterine malformation, placenta previa totalis
* Cerclage prior to randomization
* At randomisation: active vaginal bleeding and/or spontaneous rupture of membranes and/or painful regular uterine contractions
* silicone allergy
* current participation in other RCT
C: Inclusion Criteria:

* Diagnosed to be pregnant at up to 24+0 weeks of gestation, with a cervical length measurement of ≤25 mm with a singleton pregnancy, or ≤38 mm in twins pregnancy.
* Does not meet with maternal/fetal/membrane/placental factors detailed in the exclusion criteria.
* Willingness to comply with the protocol for the duration of the study.
* Have signed an informed consent.

Exclusion Criteria:

* Fetal factors: major fetal abnormalities, death of one or both of the fetuses, twins- twin-to-twin transfusion syndrome, and severe growth retardation.
* Maternal factors: prophylactic cervical cerclage in situ, painful regular uterine contractions, active labor, active vaginal bleeding, maternal age under 18, uterine abnormalities (i.e. two cervices), and severe uterine prolapse.
* Membranes and placental factors: placenta previa, ruptured membranes.
D: Inclusion Criteria:

1. Short cervical length equal or less than 20 mm
2. Singleton pregnant women between 18 -24 weeks with no prior history of preterm deliveries.
3. 18 years or older at the time of enrollment.
4. Consent to participate in the study

Exclusion Criteria:

1. Previous preterm delivery less than 37 weeks
2. Major fetal anomalies
3. Multiple pregnancy
4. Patient currently with cervical cerclage in-situ for the treatment of incompetence cervix.
5. Regular uterine contractions or significantly dilated cervical canal
6. Age less than 18 years
7. Decline to participate in the study

Answer: D