Please select the eligibility criteria that correspond to the clinical trial below.
Title: Efficacy and Safety of MgSO4 as Tocolytics Compared to Ritodrine in Preterm Labor
Brief Summary: Ritodrine is the conventional and the only approved tocolytics in Korea(by KFDA), although it was withdrawn from the US market more than 10 years ago. As already known well, ritodrine has many side effects such as tachycardia, hyperglycemia, pulmonary edema and so on. When such complications of ritodrine appears, clinicians consider of using MgSO4 as substitute, but its use is off-the-label yet in Korea. Facing this discrepancy, the investigators want to compare the efficacy and safety of MgSO4 with ritodrine and prove that MgSO4 is not inferior to ritodrine as tocolytics. For the singleton and twin pregnancies between 24+0weeks and 34 completed weeks whose uterine contraction is more than 4 during 20 minutes period with their cervical ripening is more than 25%, the investigators randomise them in Ritodrine group or MgSO4 group. Then, the investigators will check the change of their interval of uterine contraction, degree of pain and the appearance of any side effects or treatment failure sign.


Options:
A: Inclusion Criteria:

* Gestational age of 24+0 to 34+6weeks
* singleton and twin pregnancies
* preterm labor with more than 4 times of uterine contraction for 20 minutes or more than 8 times for 1 hour on external tocography
* cervical dilatation of 0 to 3cm and cervical ripening more than 25%, or cervical length in sonography below 2cm

Exclusion Criteria:

* triplet etc
* preterm premature rupture of membrane
* cervical dilatation more than 3cm
* history of cerclage operation during this pregnancy
* placenta previa
* severe hypertensive diseases in pregnancy
* history of administration of any tocolytics 12 hours before enrollment
* fever more than 38.0'c
B: Inclusion Criteria:

* Patients between 240/7-320/7 weeks gestation with findings consistent with preterm labor defined by at least one of the following criteria in accordance with regular uterine contractions (\>4 uterine contractions in 20 minutes):

  1. Cervix \> 2 cm in dilation or 80% effaced
  2. Positive fetal fibronectin (if performed).
  3. Demonstrated cervical change between two exams within 90 minutes.

Exclusion Criteria:

* Negative fetal fibronectin
* \> 5cm dilatation
* Multiple gestations
* Known fetal anomalies or chromosomal abnormalities
* Ruptured membranes
* Significant vaginal bleeding
* Suspected chorioamnionitis
* Preeclampsia or uncontrolled hypertension
* Non-reassuring fetal heart tracing
* Placenta previa and/or accreta
* Placenta abruption
* Intrauterine growth restriction
* Maternal renal disease
* Underlying maternal cardiac condition
* Symptomatic hyperthyroidism
* Significant maternal disease
* Contraindication to nifedipine or magnesium
* Cerclage presence
* Tocolytic use within the last 12 hours
* Hypotension (defined as average blood pressure of \<70/40's unresponsive to 1000 cc fluid bolus
C: Inclusion Criteria:

* English or Spanish speaking
* preterm premature rupture of membranes
* 26 - 32.6 weeks gestation
* cervical dilation \</= 4 cm

Exclusion Criteria:

* suspected intrauterine or intraamniotic infection
* \> 6 hours of tocolysis prior to admission
* positive fetal lung maturity
D: Inclusion Criteria:

* Women included in the study were diagnosed as preterm labor defined according to American Academy of Pediatrics and the American College of Obstetricians and Gynecologists (2012) with regular contractions before 37 weeks that are associated with cervical change .

Regular uterine contractions means at least 4 in 20 minutes or 8 in 60 minutes) and cervical changes are either cervical dilation more than 1 cm, and/or cervical effacement ≥ 80%. Threatened preterm labour was defined as contractions without any appreciable cervical changes. Women included were between 18 and 40 years old at gestational age between 28 and 34 weeks

Exclusion Criteria:

* Women with failed tocolytic treatment to stop uterine contractions,
* those with established preterm labor (cervical dilatation ≥ 4 cm),
* multifetal pregnancy
* fetal anomalies
* those with contraindication of continuation of pregnancy (antepartum hemorrhage, premature rupture of membranes, evidence of intrauterine infections or non reassuring fetal heart rate tracing)

Answer: A