A Phase III Efficacy and Safety Study of Intravenous Retosiban Versus Placebo for Women in Spontaneous Preterm Labor

Inclusion Criteria:

- Signed and dated written informed consent is required prior to a subject's
participation in the study and the performance of any protocol specific procedures.
Adolescents aged 12 to 17 years must provide written agreement to participate in the
study in accordance with applicable regulatory and country or state requirements.
Subjects will also be asked to sign a release for medical records at the time of
consenting to allow access to both the maternal and neonatal records including
information about delivery and infant care as well as information collected prior to
the consent having been signed.

- Females aged 12 to 45 years, with an uncomplicated, singleton pregnancy and intact
membranes in preterm.

- Gestational age between 24 and 33 weeks as determined by (1) known fertilization date,
either in vitro fertilization or intrauterine insemination, (2) last menstrual period
confirmed by the earliest ultrasound prior to 24 weeks gestation, or (3) the earliest
ultrasound alone prior to 24 weeks gestation, whichever is the most accurate method
available for each subject. In situations where prenatal ultrasound records are not
available at the time the subject presents, the investigator will make every effort to
obtain these records (either via computer records, directly from the subject's primary
care obstetrician, or via telephone). However, in cases in which these records are not
readily available (e.g., off hours, holiday), it is within the investigator's
discretion to use GA based on a verbal history from the subject with the intent of
getting confirmation from the medical records as soon as possible.

- Females must be diagnosed with preterm labor according to both of the following
criteria: a) Regular uterine contractions at a rate of >=4 contractions of at least 30
seconds' duration during a 30-minute interval confirmed by tocodynamometry and at
least 1 of the following, b) Cervical dilation >=2 centimeter (cm) and <=4 cm by
digital cervical examination or c) If <2 cm dilation by digital cervical examination,
a cervical change consisting of an increase of at least 25% effacement or 1-cm
dilation.

- Current or past tocolytic treatment as follows: a) Subjects in whom tocolytic
treatment has not been initiated prior to consent are eligible for the study, b)
Transferred or referred subjects for whom parenteral magnesium sulfate treatment has
been started before Screening are eligible provided they meet all eligibility
criteria, c) Subjects receiving a prohibited tocolytic in this study are eligible only
if the treatment is stopped before randomization and provided they meet all
eligibility criteria, d) Subjects with a historical failure of a tocolytic treatment
in a previous episode of preterm labor during the current pregnancy are eligible
provided they meet all eligibility criteria.

Exclusion Criteria:

- Fever with a temperature >100.4 degree Fahrenheit (38 degree centigrade) for more than
1 hour or >=101 degree Fahrenheit (38.3 degree centigrade) in the 24 hours prior to
the start of study treatment.

- Women with maternal-fetal conditions that potentially necessitate the need for
delivery, such as pre-eclampsia or fetal compromise.

- A fetus with any diagnosis, condition, treatment, or other factor that in the opinion
of the investigator has the potential to affect or confound assessments of efficacy or
safety (for example: nonreassuring fetal status, intrauterine growth restriction,
major congenital anomaly).

- Preterm premature rupture of membranes.

- Women with any confirmed or suspected contraindication to prolongation of pregnancy,
such as placental abruption, chorioamnionitis, or placenta previa.

- Evidence of polyhydramnios (AFI >25 cm) or oligohydramnios (AFI <5 cm).

- Women with co-morbid medical or obstetric conditions that in the opinion of the
investigator have the potential to complicate the pregnancy course and outcomes, such
as uncontrolled hypertension or uncontrolled diabetes (if known, history of
glycosylated hemoglobin >8% at any time during pregnancy), or compromise the safety of
the subject, such as underlying cardiovascular disorder (specifically ischemic cardiac
disease, congenital heart disease, pulmonary hypertension, valvular heart disease,
arrhythmias, and cardiomyopathy).

- Women with a history of substance abuse during the pregnancy or urine drug screen
positive for cocaine, phencyclidine (PCP), methamphetamine, or amphetamine.

- Women in whom the combination of history and screening test results is suggestive of
abuse or dependency that may have the potential to complicate the pregnancy outcome.

- Women with any diagnosis, condition, treatment, or other factor that, in the opinion
of the investigator, has the potential to affect or confound assessments of efficacy
or safety.

- Current active liver or biliary disease (with the exception of Gilbert's syndrome or
asymptomatic gallstones or otherwise stable chronic liver disease per investigator
assessment).

- History of sensitivity to any of the investigational products (IPs) or components
thereof or a history of drug or other allergy that, in the opinion of the investigator
or GlaxoSmithKline/ Pharmaceutical Product Development (GSK/PPD) medical monitor,
contraindicates the subject's participation.